Provided by: libconvert-binary-c-perl_0.76-3build1_amd64 
NAME
Convert::Binary::C - Binary Data Conversion using C Types
SYNOPSIS
Simple
use Convert::Binary::C;
#---------------------------------------------
# Create a new object and parse embedded code
#---------------------------------------------
my $c = Convert::Binary::C->new->parse(<<ENDC);
enum Month { JAN, FEB, MAR, APR, MAY, JUN,
JUL, AUG, SEP, OCT, NOV, DEC };
struct Date {
int year;
enum Month month;
int day;
};
ENDC
#-----------------------------------------------
# Pack Perl data structure into a binary string
#-----------------------------------------------
my $date = { year => 2002, month => 'DEC', day => 24 };
my $packed = $c->pack('Date', $date);
Advanced
use Convert::Binary::C;
use Data::Dumper;
#---------------------
# Create a new object
#---------------------
my $c = new Convert::Binary::C ByteOrder => 'BigEndian';
#---------------------------------------------------
# Add include paths and global preprocessor defines
#---------------------------------------------------
$c->Include('/usr/lib/gcc/i686-pc-linux-gnu/4.5.2/include',
'/usr/lib/gcc/i686-pc-linux-gnu/4.5.2/include-fixed',
'/usr/include')
->Define(qw( __USE_POSIX __USE_ISOC99=1 ));
#----------------------------------
# Parse the 'time.h' header file
#----------------------------------
$c->parse_file('time.h');
#---------------------------------------
# See which files the object depends on
#---------------------------------------
print Dumper([$c->dependencies]);
#-----------------------------------------------------------
# See if struct timespec is defined and dump its definition
#-----------------------------------------------------------
if ($c->def('struct timespec')) {
print Dumper($c->struct('timespec'));
}
#-------------------------------
# Create some binary dummy data
#-------------------------------
my $data = "binary_test_string";
#--------------------------------------------------------
# Unpack $data according to 'struct timespec' definition
#--------------------------------------------------------
if (length($data) >= $c->sizeof('timespec')) {
my $perl = $c->unpack('timespec', $data);
print Dumper($perl);
}
#--------------------------------------------------------
# See which member lies at offset 5 of 'struct timespec'
#--------------------------------------------------------
my $member = $c->member('timespec', 5);
print "member('timespec', 5) = '$member'\n";
DESCRIPTION
Convert::Binary::C is a preprocessor and parser for C type definitions. It is highly
configurable and supports arbitrarily complex data structures. Its object-oriented
interface has "pack" and "unpack" methods that act as replacements for Perl's "pack" and
"unpack" and allow to use C types instead of a string representation of the data structure
for conversion of binary data from and to Perl's complex data structures.
Actually, what Convert::Binary::C does is not very different from what a C compiler does,
just that it doesn't compile the source code into an object file or executable, but only
parses the code and allows Perl to use the enumerations, structs, unions and typedefs that
have been defined within your C source for binary data conversion, similar to Perl's
"pack" and "unpack".
Beyond that, the module offers a lot of convenience methods to retrieve information about
the C types that have been parsed.
Background and History
In late 2000 I wrote a real-time debugging interface for an embedded medical device that
allowed me to send out data from that device over its integrated Ethernet adapter. The
interface was "printf()"-like, so you could easily send out strings or numbers. But you
could also send out what I called arbitrary data, which was intended for arbitrary blocks
of the device's memory.
Another part of this real-time debugger was a Perl application running on my workstation
that gathered all the messages that were sent out from the embedded device. It printed all
the strings and numbers, and hex-dumped the arbitrary data. However, manually parsing a
couple of 300 byte hex-dumps of a complex C structure is not only frustrating, but also
error-prone and time consuming.
Using "unpack" to retrieve the contents of a C structure works fine for small structures
and if you don't have to deal with struct member alignment. But otherwise, maintaining
such code can be as awful as deciphering hex-dumps.
As I didn't find anything to solve my problem on the CPAN, I wrote a little module that
translated simple C structs into "unpack" strings. It worked, but it was slow. And since
it couldn't deal with struct member alignment, I soon found myself adding padding bytes
everywhere. So again, I had to maintain two sources, and changing one of them forced me
to touch the other one.
All in all, this little module seemed to make my task a bit easier, but it was far from
being what I was thinking of:
• A module that could directly use the source I've been coding for the embedded device
without any modifications.
• A module that could be configured to match the properties of the different compilers and
target platforms I was using.
• A module that was fast enough to decode a great amount of binary data even on my slow
workstation.
I didn't know how to accomplish these tasks until I read something about XS. At least, it
seemed as if it could solve my performance problems. However, writing a C parser in C
isn't easier than it is in Perl. But writing a C preprocessor from scratch is even worse.
Fortunately enough, after a few weeks of searching I found both, a lean, open-source C
preprocessor library, and a reusable YACC grammar for ANSI-C. That was the beginning of
the development of Convert::Binary::C in late 2001.
Now, I'm successfully using the module in my embedded environment since long before it
appeared on CPAN. From my point of view, it is exactly what I had in mind. It's fast,
flexible, easy to use and portable. It doesn't require external programs or other Perl
modules.
About this document
This document describes how to use Convert::Binary::C. A lot of different features are
presented, and the example code sometimes uses Perl's more advanced language elements. If
your experience with Perl is rather limited, you should know how to use Perl's very good
documentation system.
To look up one of the manpages, use the "perldoc" command. For example,
perldoc perl
will show you Perl's main manpage. To look up a specific Perl function, use "perldoc -f":
perldoc -f map
gives you more information about the "map" function. You can also search the FAQ using
"perldoc -q":
perldoc -q array
will give you everything you ever wanted to know about Perl arrays. But now, let's go on
with some real stuff!
Why use Convert::Binary::C?
Say you want to pack (or unpack) data according to the following C structure:
struct foo {
char ary[3];
unsigned short baz;
int bar;
};
You could of course use Perl's "pack" and "unpack" functions:
@ary = (1, 2, 3);
$baz = 40000;
$bar = -4711;
$binary = pack 'c3 S i', @ary, $baz, $bar;
But this implies that the struct members are byte aligned. If they were long aligned
(which is the default for most compilers), you'd have to write
$binary = pack 'c3 x S x2 i', @ary, $baz, $bar;
which doesn't really increase readability.
Now imagine that you need to pack the data for a completely different architecture with
different byte order. You would look into the "pack" manpage again and perhaps come up
with this:
$binary = pack 'c3 x n x2 N', @ary, $baz, $bar;
However, if you try to unpack $foo again, your signed values have turned into unsigned
ones.
All this can still be managed with Perl. But imagine your structures get more complex?
Imagine you need to support different platforms? Imagine you need to make changes to the
structures? You'll not only have to change the C source but also dozens of "pack" strings
in your Perl code. This is no fun. And Perl should be fun.
Now, wouldn't it be great if you could just read in the C source you've already written
and use all the types defined there for packing and unpacking? That's what
Convert::Binary::C does.
Creating a Convert::Binary::C object
To use Convert::Binary::C just say
use Convert::Binary::C;
to load the module. Its interface is completely object oriented, so it doesn't export any
functions.
Next, you need to create a new Convert::Binary::C object. This can be done by either
$c = Convert::Binary::C->new;
or
$c = new Convert::Binary::C;
You can optionally pass configuration options to the constructor as described in the next
section.
Configuring the object
To configure a Convert::Binary::C object, you can either call the "configure" method or
directly pass the configuration options to the constructor. If you want to change byte
order and alignment, you can use
$c->configure(ByteOrder => 'LittleEndian',
Alignment => 2);
or you can change the construction code to
$c = new Convert::Binary::C ByteOrder => 'LittleEndian',
Alignment => 2;
Either way, the object will now know that it should use little endian (Intel) byte order
and 2-byte struct member alignment for packing and unpacking.
Alternatively, you can use the option names as names of methods to configure the object,
like:
$c->ByteOrder('LittleEndian');
You can also retrieve information about the current configuration of a Convert::Binary::C
object. For details, see the section about the "configure" method.
Parsing C code
Convert::Binary::C allows two ways of parsing C source. Either by parsing external C
header or C source files:
$c->parse_file('header.h');
Or by parsing C code embedded in your script:
$c->parse(<<'CCODE');
struct foo {
char ary[3];
unsigned short baz;
int bar;
};
CCODE
Now the object $c will know everything about "struct foo". The example above uses a so-
called here-document. It allows one to easily embed multi-line strings in your code. You
can find more about here-documents in perldata or perlop.
Since the "parse" and "parse_file" methods throw an exception when a parse error occurs,
you usually want to catch these in an "eval" block:
eval { $c->parse_file('header.h') };
if ($@) {
# handle error appropriately
}
Perl's special $@ variable will contain an empty string (which evaluates to a false value
in boolean context) on success or an error string on failure.
As another feature, "parse" and "parse_file" return a reference to their object on
success, just like "configure" does when you're configuring the object. This will allow
you to write constructs like this:
my $c = eval {
Convert::Binary::C->new(Include => ['/usr/include'])
->parse_file('header.h')
};
if ($@) {
# handle error appropriately
}
Packing and unpacking
Convert::Binary::C has two methods, "pack" and "unpack", that act similar to the functions
of same denominator in Perl. To perform the packing described in the example above, you
could write:
$data = {
ary => [1, 2, 3],
baz => 40000,
bar => -4711,
};
$binary = $c->pack('foo', $data);
Unpacking will work exactly the same way, just that the "unpack" method will take a byte
string as its input and will return a reference to a (possibly very complex) Perl data
structure.
$binary = get_data_from_memory();
$data = $c->unpack('foo', $binary);
You can now easily access all of the values:
print "foo.ary[1] = $data->{ary}[1]\n";
Or you can even more conveniently use the Data::Dumper module:
use Data::Dumper;
print Dumper($data);
The output would look something like this:
$VAR1 = {
'bar' => -271,
'baz' => 5000,
'ary' => [
42,
48,
100
]
};
Preprocessor configuration
Convert::Binary::C uses Thomas Pornin's "ucpp" as an internal C preprocessor. It is
compliant to ISO-C99, so you don't have to worry about using even weird preprocessor
constructs in your code.
If your C source contains includes or depends upon preprocessor defines, you may need to
configure the internal preprocessor. Use the "Include" and "Define" configuration options
for that:
$c->configure(Include => ['/usr/include',
'/home/mhx/include'],
Define => [qw( NDEBUG FOO=42 )]);
If your code uses system includes, it is most likely that you will need to define the
symbols that are usually defined by the compiler.
On some operating systems, the system includes require the preprocessor to predefine a
certain set of assertions. Assertions are supported by "ucpp", and you can define them
either in the source code using "#assert" or as a property of the Convert::Binary::C
object using "Assert":
$c->configure(Assert => ['predicate(answer)']);
Information about defined macros can be retrieved from the preprocessor as long as its
configuration isn't changed. The preprocessor is implicitly reset if you change one of the
following configuration options:
Include
Define
Assert
HasCPPComments
HasMacroVAARGS
Supported pragma directives
Convert::Binary::C supports the "pack" pragma to locally override struct member alignment.
The supported syntax is as follows:
#pragma pack( ALIGN )
Sets the new alignment to ALIGN. If ALIGN is 0, resets the alignment to its original
value.
#pragma pack
Resets the alignment to its original value.
#pragma pack( push, ALIGN )
Saves the current alignment on a stack and sets the new alignment to ALIGN. If ALIGN
is 0, sets the alignment to the default alignment.
#pragma pack( pop )
Restores the alignment to the last value saved on the stack.
/* Example assumes sizeof( short ) == 2, sizeof( long ) == 4. */
#pragma pack(1)
struct nopad {
char a; /* no padding bytes between 'a' and 'b' */
long b;
};
#pragma pack /* reset to "native" alignment */
#pragma pack( push, 2 )
struct pad {
char a; /* one padding byte between 'a' and 'b' */
long b;
#pragma pack( push, 1 )
struct {
char c; /* no padding between 'c' and 'd' */
short d;
} e; /* sizeof( e ) == 3 */
#pragma pack( pop ); /* back to pack( 2 ) */
long f; /* one padding byte between 'e' and 'f' */
};
#pragma pack( pop ); /* back to "native" */
The "pack" pragma as it is currently implemented only affects the maximum struct member
alignment. There are compilers that also allow to specify the minimum struct member
alignment. This is not supported by Convert::Binary::C.
Automatic configuration using "ccconfig"
As there are over 20 different configuration options, setting all of them correctly can be
a lengthy and tedious task.
The "ccconfig" script, which is bundled with this module, aims at automatically
determining the correct compiler configuration by testing the compiler executable. It
works for both, native and cross compilers.
UNDERSTANDING TYPES
This section covers one of the fundamental features of Convert::Binary::C. It's how type
expressions, referred to as TYPEs in the method reference, are handled by the module.
Many of the methods, namely "pack", "unpack", "sizeof", "typeof", "member", "offsetof",
"def", "initializer" and "tag", are passed a TYPE to operate on as their first argument.
Standard Types
These are trivial. Standard types are simply enum names, struct names, union names, or
typedefs. Almost every method that wants a TYPE will accept a standard type.
For enums, structs and unions, the prefixes "enum", "struct" and "union" are optional.
However, if a typedef with the same name exists, like in
struct foo {
int bar;
};
typedef int foo;
you will have to use the prefix to distinguish between the struct and the typedef.
Otherwise, a typedef is always given preference.
Basic Types
Basic types, or atomic types, are "int" or "char", for example. It's possible to use
these basic types without having parsed any code. You can simply do
$c = new Convert::Binary::C;
$size = $c->sizeof('unsigned long');
$data = $c->pack('short int', 42);
Even though the above works fine, it is not possible to define more complex types on the
fly, so
$size = $c->sizeof('struct { int a, b; }');
will result in an error.
Basic types are not supported by all methods. For example, it makes no sense to use
"member" or "offsetof" on a basic type. Using "typeof" isn't very useful, but supported.
Member Expressions
This is by far the most complex part, depending on the complexity of your data structures.
Any standard type that defines a compound or an array may be followed by a member
expression to select only a certain part of the data type. Say you have parsed the
following C code:
struct foo {
long type;
struct {
short x, y;
} array[20];
};
typedef struct foo matrix[8][8];
You may want to know the size of the "array" member of "struct foo". This is quite easy:
print $c->sizeof('foo.array'), " bytes";
will print
80 bytes
depending of course on the "ShortSize" you configured.
If you wanted to unpack only a single column of "matrix", that's easy as well (and of
course it doesn't matter which index you use):
$column = $c->unpack('matrix[2]', $data);
Just like in C, it is possible to use out-of-bounds array indices. This means that, for
example, despite "array" is declared to have 20 elements, the following code
$size = $c->sizeof('foo.array[4711]');
$offset = $c->offsetof('foo', 'array[-13]');
is perfectly valid and will result in:
$size = 4
$offset = -48
Member expressions can be arbitrarily complex:
$type = $c->typeof('matrix[2][3].array[7].y');
print "the type is $type";
will, for example, print
the type is short
Member expressions are also used as the second argument to "offsetof".
Offsets
Members returned by the "member" method have an optional offset suffix to indicate that
the given offset doesn't point to the start of that member. For example,
$member = $c->member('matrix', 1431);
print $member;
will print
[2][1].type+3
If you would use this as a member expression, like in
$size = $c->sizeof("matrix $member");
the offset suffix will simply be ignored. Actually, it will be ignored for all methods if
it's used in the first argument.
When used in the second argument to "offsetof", it will usually do what you mean, i. e.
the offset suffix, if present, will be considered when determining the offset. This
behaviour ensures that
$member = $c->member('foo', 43);
$offset = $c->offsetof('foo', $member);
print "'$member' is located at offset $offset of struct foo";
will always correctly set $offset:
'.array[9].y+1' is located at offset 43 of struct foo
If this is not what you mean, e.g. because you want to know the offset where the member
returned by "member" starts, you just have to remove the suffix:
$member =~ s/\+\d+$//;
$offset = $c->offsetof('foo', $member);
print "'$member' starts at offset $offset of struct foo";
This would then print:
'.array[9].y' starts at offset 42 of struct foo
USING TAGS
In a nutshell, tags are properties that you can attach to types.
You can add tags to types using the "tag" method, and remove them using "tag" or "untag",
for example:
# Attach 'Format' and 'Hooks' tags
$c->tag('type', Format => 'String', Hooks => { pack => \&rout });
$c->untag('type', 'Format'); # Remove only 'Format' tag
$c->untag('type'); # Remove all tags
You can also use "tag" to see which tags are attached to a type, for example:
$tags = $c->tag('type');
This would give you:
$tags = {
'Hooks' => {
'pack' => \&rout
},
'Format' => 'String'
};
Currently, there are only a couple of different tags that influence the way data is packed
and unpacked. There are probably more tags to come in the future.
The Format Tag
One of the tags currently available is the "Format" tag. Using this tag, you can tell a
Convert::Binary::C object to pack and unpack a certain data type in a special way.
For example, if you have a (fixed length) string type
typedef char str_type[40];
this type would, by default, be unpacked as an array of "char"s. That's because it is only
an array of "char"s, and Convert::Binary::C doesn't know it is actually used as a string.
But you can tell Convert::Binary::C that "str_type" is a C string using the "Format" tag:
$c->tag('str_type', Format => 'String');
This will make "unpack" (and of course also "pack") treat the binary data like a null-
terminated C string:
$binary = "Hello World!\n\0 this is just some dummy data";
$hello = $c->unpack('str_type', $binary);
print $hello;
would thusly print:
Hello World!
Of course, this also works the other way round:
use Data::Hexdumper;
$binary = $c->pack('str_type', "Just another C::B::C hacker");
print hexdump(data => $binary);
would print:
0x0000 : 4A 75 73 74 20 61 6E 6F 74 68 65 72 20 43 3A 3A : Just.another.C::
0x0010 : 42 3A 3A 43 20 68 61 63 6B 65 72 00 00 00 00 00 : B::C.hacker.....
0x0020 : 00 00 00 00 00 00 00 00 : ........
If you want Convert::Binary::C to not interpret the binary data at all, you can set the
"Format" tag to "Binary". This might not be seem very useful, as "pack" and "unpack"
would just pass through the unmodified binary data. But you can tag not only whole types,
but also compound members. For example
$c->parse(<<ENDC);
struct packet {
unsigned short header;
unsigned short flags;
unsigned char payload[28];
};
ENDC
$c->tag('packet.payload', Format => 'Binary');
would allow you to write:
read FILE, $payload, $c->sizeof('packet.payload');
$packet = {
header => 4711,
flags => 0xf00f,
payload => $payload,
};
$binary = $c->pack('packet', $packet);
print hexdump(data => $binary);
This would print something like:
0x0000 : 12 67 F0 0F 6E 6F 0A 6E 6F 0A 6E 6F 0A 6E 6F 0A : .g..no.no.no.no.
0x0010 : 6E 6F 0A 6E 6F 0A 6E 6F 0A 6E 6F 0A 6E 6F 0A 6E : no.no.no.no.no.n
For obvious reasons, it is not allowed to attach a "Format" tag to bitfield members.
Trying to do so will result in an exception being thrown by the "tag" method.
The ByteOrder Tag
The "ByteOrder" tag allows you to override the byte order of certain types or members. The
implementation of this tag is considered experimental and may be subject to changes in the
future.
Usually it doesn't make much sense to override the byte order, but there may be
applications where a sub-structure is packed in a different byte order than the
surrounding structure.
Take, for example, the following code:
$c = Convert::Binary::C->new(ByteOrder => 'BigEndian',
OrderMembers => 1);
$c->parse(<<'ENDC');
typedef unsigned short u_16;
struct coords_3d {
long x, y, z;
};
struct coords_msg {
u_16 header;
u_16 length;
struct coords_3d coords;
};
ENDC
Assume that while "coords_msg" is big endian, the embedded coordinates "coords_3d" are
stored in little endian format for some reason. In C, you'll have to handle this manually.
But using Convert::Binary::C, you can simply attach a "ByteOrder" tag to either the
"coords_3d" structure or to the "coords" member of the "coords_msg" structure. Both will
work in this case. The only difference is that if you tag the "coords" member, "coords_3d"
will only be treated as little endian if you "pack" or "unpack" the "coords_msg"
structure. (BTW, you could also tag all members of "coords_3d" individually, but that
would be inefficient.)
So, let's attach the "ByteOrder" tag to the "coords" member:
$c->tag('coords_msg.coords', ByteOrder => 'LittleEndian');
Assume the following binary message:
0x0000 : 00 2A 00 0C FF FF FF FF 02 00 00 00 2A 00 00 00 : .*..........*...
If you unpack this message...
$msg = $c->unpack('coords_msg', $binary);
...you will get the following data structure:
$msg = {
'header' => 42,
'length' => 12,
'coords' => {
'x' => -1,
'y' => 2,
'z' => 42
}
};
Without the "ByteOrder" tag, you would get:
$msg = {
'header' => 42,
'length' => 12,
'coords' => {
'x' => -1,
'y' => 33554432,
'z' => 704643072
}
};
The "ByteOrder" tag is a recursive tag, i.e. it applies to all children of the tagged
object recursively. Of course, it is also possible to override a "ByteOrder" tag by
attaching another "ByteOrder" tag to a child type. Confused? Here's an example. In
addition to tagging the "coords" member as little endian, we now tag "coords_3d.y" as big
endian:
$c->tag('coords_3d.y', ByteOrder => 'BigEndian');
$msg = $c->unpack('coords_msg', $binary);
This will return the following data structure:
$msg = {
'header' => 42,
'length' => 12,
'coords' => {
'x' => -1,
'y' => 33554432,
'z' => 42
}
};
Note that if you tag both a type and a member of that type within a compound, the tag
attached to the type itself has higher precedence. Using the example above, if you would
attach a "ByteOrder" tag to both "coords_msg.coords" and "coords_3d", the tag attached to
"coords_3d" would always win.
Also note that the "ByteOrder" tag might not work as expected along with bitfields, which
is why the implementation is considered experimental. Bitfields are currently not affected
by the "ByteOrder" tag at all. This is because the byte order would affect the bitfield
layout, and a consistent implementation supporting multiple layouts of the same struct
would be quite bulky and probably slow down the whole module.
If you really need the correct behaviour, you can use the following trick:
$le = Convert::Binary::C->new(ByteOrder => 'LittleEndian');
$le->parse(<<'ENDC');
typedef unsigned short u_16;
typedef unsigned long u_32;
struct message {
u_16 header;
u_16 length;
struct {
u_32 a;
u_32 b;
u_32 c : 7;
u_32 d : 5;
u_32 e : 20;
} data;
};
ENDC
$be = $le->clone->ByteOrder('BigEndian');
$le->tag('message.data', Format => 'Binary', Hooks => {
unpack => sub { $be->unpack('message.data', @_) },
pack => sub { $be->pack('message.data', @_) },
});
$msg = $le->unpack('message', $binary);
This uses the "Format" and "Hooks" tags along with a big endian "clone" of the original
little endian object. It attaches hooks to the little endian object and in the hooks it
uses the big endian object to "pack" and "unpack" the binary data.
The Dimension Tag
The "Dimension" tag allows you to override the declared dimension of an array for packing
or unpacking data. The implementation of this tag is considered very experimental and will
definitely change in a future release.
That being said, the "Dimension" tag is primarily useful to support variable length
arrays. Usually, you have to write the following code for such a variable length array in
C:
struct c_message
{
unsigned count;
char data[1];
};
So, because you cannot declare an empty array, you declare an array with a single element.
If you have a ISO-C99 compliant compiler, you can write this code instead:
struct c99_message
{
unsigned count;
char data[];
};
This explicitly tells the compiler that "data" is a flexible array member.
Convert::Binary::C already uses this information to handle flexible array members in a
special way.
As you can see in the following example, the two types are treated differently:
$data = pack 'NC*', 3, 1..8;
$uc = $c->unpack('c_message', $data);
$uc99 = $c->unpack('c99_message', $data);
This will result in:
$uc = {'count' => 3,'data' => [1]};
$uc99 = {'count' => 3,'data' => [1,2,3,4,5,6,7,8]};
However, only few compilers support ISO-C99, and you probably don't want to change your
existing code only to get some extra features when using Convert::Binary::C.
So it is possible to attach a tag to the "data" member of the "c_message" struct that
tells Convert::Binary::C to treat the array as if it were flexible:
$c->tag('c_message.data', Dimension => '*');
Now both "c_message" and "c99_message" will behave exactly the same when using "pack" or
"unpack". Repeating the above code:
$uc = $c->unpack('c_message', $data);
This will result in:
$uc = {'count' => 3,'data' => [1,2,3,4,5,6,7,8]};
But there's more you can do. Even though it probably doesn't make much sense, you can tag
a fixed dimension to an array:
$c->tag('c_message.data', Dimension => '5');
This will obviously result in:
$uc = {'count' => 3,'data' => [1,2,3,4,5]};
A more useful way to use the "Dimension" tag is to set it to the name of a member in the
same compound:
$c->tag('c_message.data', Dimension => 'count');
Convert::Binary::C will now use the value of that member to determine the size of the
array, so unpacking will result in:
$uc = {'count' => 3,'data' => [1,2,3]};
Of course, you can also tag flexible array members. And yes, it's also possible to use
more complex member expressions:
$c->parse(<<ENDC);
struct msg_header
{
unsigned len[2];
};
struct more_complex
{
struct msg_header hdr;
char data[];
};
ENDC
$data = pack 'NNC*', 42, 7, 1 .. 10;
$c->tag('more_complex.data', Dimension => 'hdr.len[1]');
$u = $c->unpack('more_complex', $data);
The result will be:
$u = {
'hdr' => {
'len' => [
42,
7
]
},
'data' => [
1,
2,
3,
4,
5,
6,
7
]
};
By the way, it's also possible to tag arrays that are not embedded inside a compound:
$c->parse(<<ENDC);
typedef unsigned short short_array[];
ENDC
$c->tag('short_array', Dimension => '5');
$u = $c->unpack('short_array', $data);
Resulting in:
$u = [0,42,0,7,258];
The final and most powerful way to define a "Dimension" tag is to pass it a subroutine
reference. The referenced subroutine can execute whatever code is necessary to determine
the size of the tagged array:
sub get_size
{
my $m = shift;
return $m->{hdr}{len}[0] / $m->{hdr}{len}[1];
}
$c->tag('more_complex.data', Dimension => \&get_size);
$u = $c->unpack('more_complex', $data);
As you can guess from the above code, the subroutine is being passed a reference to hash
that stores the already unpacked part of the compound embedding the tagged array. This is
the result:
$u = {
'hdr' => {
'len' => [
42,
7
]
},
'data' => [
1,
2,
3,
4,
5,
6
]
};
You can also pass custom arguments to the subroutines by using the "arg" method. This is
similar to the functionality offered by the "Hooks" tag.
Of course, all that also works for the "pack" method as well.
However, the current implementation has at least one shortcomings, which is why it's
experimental: The "Dimension" tag doesn't impact compound layout. This means that while
you can alter the size of an array in the middle of a compound, the offset of the members
after that array won't be impacted. I'd rather like to see the layout adapt dynamically,
so this is what I'm hoping to implement in the future.
The Hooks Tag
Hooks are a special kind of tag that can be extremely useful.
Using hooks, you can easily override the way "pack" and "unpack" handle data using your
own subroutines. If you define hooks for a certain data type, each time this data type is
processed the corresponding hook will be called to allow you to modify that data.
Basic Hooks
Here's an example. Let's assume the following C code has been parsed:
typedef unsigned long u_32;
typedef u_32 ProtoId;
typedef ProtoId MyProtoId;
struct MsgHeader {
MyProtoId id;
u_32 len;
};
struct String {
u_32 len;
char buf[];
};
You could now use the types above and, for example, unpack binary data representing a
"MsgHeader" like this:
$msg_header = $c->unpack('MsgHeader', $data);
This would give you:
$msg_header = {
'len' => 13,
'id' => 42
};
Instead of dealing with "ProtoId"'s as integers, you would rather like to have them as
clear text. You could provide subroutines to convert between clear text and integers:
%proto = (
CATS => 1,
DOGS => 42,
HEDGEHOGS => 4711,
);
%rproto = reverse %proto;
sub ProtoId_unpack {
$rproto{$_[0]} || 'unknown protocol'
}
sub ProtoId_pack {
$proto{$_[0]} or die 'unknown protocol'
}
You can now register these subroutines by attaching a "Hooks" tag to "ProtoId" using the
"tag" method:
$c->tag('ProtoId', Hooks => { pack => \&ProtoId_pack,
unpack => \&ProtoId_unpack });
Doing exactly the same unpack on "MsgHeader" again would now return:
$msg_header = {
'len' => 13,
'id' => 'DOGS'
};
Actually, if you don't need the reverse operation, you don't even have to register a
"pack" hook. Or, even better, you can have a more intelligent "unpack" hook that creates a
dual-typed variable:
use Scalar::Util qw(dualvar);
sub ProtoId_unpack2 {
dualvar $_[0], $rproto{$_[0]} || 'unknown protocol'
}
$c->tag('ProtoId', Hooks => { unpack => \&ProtoId_unpack2 });
$msg_header = $c->unpack('MsgHeader', $data);
Just as before, this would print
$msg_header = {
'len' => 13,
'id' => 'DOGS'
};
but without requiring a "pack" hook for packing, at least as long as you keep the variable
dual-typed.
Hooks are usually called with exactly one argument, which is the data that should be
processed (see "Advanced Hooks" for details on how to customize hook arguments). They are
called in scalar context and expected to return the processed data.
To get rid of registered hooks, you can either undefine only certain hooks
$c->tag('ProtoId', Hooks => { pack => undef });
or all hooks:
$c->tag('ProtoId', Hooks => undef);
Of course, hooks are not restricted to handling integer values. You could just as well
attach hooks for the "String" struct from the code above. A useful example would be to
have these hooks:
sub string_unpack {
my $s = shift;
pack "c$s->{len}", @{$s->{buf}};
}
sub string_pack {
my $s = shift;
return {
len => length $s,
buf => [ unpack 'c*', $s ],
}
}
(Don't be confused by the fact that the "unpack" hook uses "pack" and the "pack" hook uses
"unpack". And also see "Advanced Hooks" for a more clever approach.)
While you would normally get the following output when unpacking a "String"
$string = {
'len' => 12,
'buf' => [
72,
101,
108,
108,
111,
32,
87,
111,
114,
108,
100,
33
]
};
you could just register the hooks using
$c->tag('String', Hooks => { pack => \&string_pack,
unpack => \&string_unpack });
and you would get a nice human-readable Perl string:
$string = 'Hello World!';
Packing a string turns out to be just as easy:
use Data::Hexdumper;
$data = $c->pack('String', 'Just another Perl hacker,');
print hexdump(data => $data);
This would print:
0x0000 : 00 00 00 19 4A 75 73 74 20 61 6E 6F 74 68 65 72 : ....Just.another
0x0010 : 20 50 65 72 6C 20 68 61 63 6B 65 72 2C : .Perl.hacker,
If you want to find out if or which hooks are registered for a certain type, you can also
use the "tag" method:
$hooks = $c->tag('String', 'Hooks');
This would return:
$hooks = {
'unpack' => \&string_unpack,
'pack' => \&string_pack
};
Advanced Hooks
It is also possible to combine hooks with using the "Format" tag. This can be useful if
you know better than Convert::Binary::C how to interpret the binary data. In the previous
section, we've handled this type
struct String {
u_32 len;
char buf[];
};
with the following hooks:
sub string_unpack {
my $s = shift;
pack "c$s->{len}", @{$s->{buf}};
}
sub string_pack {
my $s = shift;
return {
len => length $s,
buf => [ unpack 'c*', $s ],
}
}
$c->tag('String', Hooks => { pack => \&string_pack,
unpack => \&string_unpack });
As you can see in the hook code, "buf" is expected to be an array of characters. For the
"unpack" case Convert::Binary::C first turns the binary data into a Perl array, and then
the hook packs it back into a string. The intermediate array creation and destruction is
completely useless. Same thing, of course, for the "pack" case.
Here's a clever way to handle this. Just tag "buf" as binary
$c->tag('String.buf', Format => 'Binary');
and use the following hooks instead:
sub string_unpack2 {
my $s = shift;
substr $s->{buf}, 0, $s->{len};
}
sub string_pack2 {
my $s = shift;
return {
len => length $s,
buf => $s,
}
}
$c->tag('String', Hooks => { pack => \&string_pack2,
unpack => \&string_unpack2 });
This will be exactly equivalent to the old code, but faster and probably even much easier
to understand.
But hooks are even more powerful. You can customize the arguments that are passed to your
hooks and you can use "arg" to pass certain special arguments, such as the name of the
type that is currently being processed by the hook.
The following example shows how it is easily possible to peek into the perl internals
using hooks.
use Config;
$c = new Convert::Binary::C %CC, OrderMembers => 1;
$c->Include(["$Config{archlib}/CORE", @{$c->Include}]);
$c->parse(<<ENDC);
#include "EXTERN.h"
#include "perl.h"
ENDC
$c->tag($_, Hooks => { unpack_ptr => [\&unpack_ptr,
$c->arg(qw(SELF TYPE DATA))] })
for qw( XPVAV XPVHV );
First, we add the perl core include path and parse perl.h. Then, we add an "unpack_ptr"
hook for a couple of the internal data types.
The "unpack_ptr" and "pack_ptr" hooks are called whenever a pointer to a certain data
structure is processed. This is by far the most experimental part of the hooks feature, as
this includes any kind of pointer. There's no way for the hook to know the difference
between a plain pointer, or a pointer to a pointer, or a pointer to an array (this is
because the difference doesn't matter anywhere else in Convert::Binary::C).
But the hook above makes use of another very interesting feature: It uses "arg" to pass
special arguments to the hook subroutine. Usually, the hook subroutine is simply passed a
single data argument. But using the above definition, it'll get a reference to the
calling object ("SELF"), the name of the type being processed ("TYPE") and the data
("DATA").
But how does our hook look like?
sub unpack_ptr {
my($self, $type, $ptr) = @_;
$ptr or return '<NULL>';
my $size = $self->sizeof($type);
$self->unpack($type, unpack("P$size", pack('I', $ptr)));
}
As you can see, the hook is rather simple. First, it receives the arguments mentioned
above. It performs a quick check if the pointer is "NULL" and shouldn't be processed any
further. Next, it determines the size of the type being processed. And finally, it'll just
use the "P"n unpack template to read from that memory location and recursively call
"unpack" to unpack the type. (And yes, this may of course again call other hooks.)
Now, let's test that:
my $ref = { foo => 42, bar => 4711 };
my $ptr = hex(("$ref" =~ /\(0x([[:xdigit:]]+)\)$/)[0]);
print Dumper(unpack_ptr($c, 'AV', $ptr));
Just for the fun of it, we create a blessed array reference. But how do we get a pointer
to the corresponding "AV"? This is rather easy, as the address of the "AV" is just the hex
value that appears when using the array reference in string context. So we just grab that
and turn it into decimal. All that's left to do is just call our hook, as it can already
handle "AV" pointers. And this is what we get:
$VAR1 = {
'sv_any' => {
'xnv_u' => {
'xnv_nv' => '0',
'xgv_stash' => 0,
'xpad_cop_seq' => {
'xlow' => 0,
'xhigh' => 0
},
'xbm_s' => {
'xbm_previous' => 0,
'xbm_flags' => 0,
'xbm_rare' => 0
}
},
'xav_fill' => 2,
'xav_max' => 7,
'xiv_u' => {
'xivu_iv' => 2,
'xivu_uv' => 2,
'xivu_p1' => 2,
'xivu_i32' => 2,
'xivu_namehek' => 2,
'xivu_hv' => 2
},
'xmg_u' => {
'xmg_magic' => 0,
'xmg_ourstash' => 0
},
'xmg_stash' => 0
},
'sv_refcnt' => 1,
'sv_flags' => 536870924,
'sv_u' => {
'svu_pv' => 142054140,
'svu_iv' => 142054140,
'svu_uv' => 142054140,
'svu_rv' => 142054140,
'svu_array' => 142054140,
'svu_hash' => 142054140,
'svu_gp' => 142054140
}
};
Even though it is rather easy to do such stuff using "unpack_ptr" hooks, you should really
know what you're doing and do it with extreme care because of the limitations mentioned
above. It's really easy to run into segmentation faults when you're dereferencing pointers
that point to memory which you don't own.
Performance
Using hooks isn't for free. In performance-critical applications you have to keep in mind
that hooks are actually perl subroutines and that they are called once for every value of
a registered type that is being packed or unpacked. If only about 10% of the values
require hooks to be called, you'll hardly notice the difference (if your hooks are
implemented efficiently, that is). But if all values would require hooks to be called,
that alone could easily make packing and unpacking very slow.
Tag Order
Since it is possible to attach multiple tags to a single type, the order in which the tags
are processed is important. Here's a small table that shows the processing order.
pack unpack
---------------------
Hooks Format
Format ByteOrder
ByteOrder Hooks
As a general rule, the "Hooks" tag is always the first thing processed when packing data,
and the last thing processed when unpacking data.
The "Format" and "ByteOrder" tags are exclusive, but when both are given the "Format" tag
wins.
METHODS
new
"new"
"new" OPTION1 => VALUE1, OPTION2 => VALUE2, ...
The constructor is used to create a new Convert::Binary::C object. You can simply
use
$c = new Convert::Binary::C;
without additional arguments to create an object, or you can optionally pass any
arguments to the constructor that are described for the "configure" method.
configure
"configure"
"configure" OPTION
"configure" OPTION1 => VALUE1, OPTION2 => VALUE2, ...
This method can be used to configure an existing Convert::Binary::C object or to
retrieve its current configuration.
To configure the object, the list of options consists of key and value pairs and
must therefore contain an even number of elements. "configure" (and also "new" if
used with configuration options) will throw an exception if you pass an odd number
of elements. Configuration will normally look like this:
$c->configure(ByteOrder => 'BigEndian', IntSize => 2);
To retrieve the current value of a configuration option, you must pass a single
argument to "configure" that holds the name of the option, just like
$order = $c->configure('ByteOrder');
If you want to get the values of all configuration options at once, you can call
"configure" without any arguments and it will return a reference to a hash table
that holds the whole object configuration. This can be conveniently used with the
Data::Dumper module, for example:
use Convert::Binary::C;
use Data::Dumper;
$c = new Convert::Binary::C Define => ['DEBUGGING', 'FOO=123'],
Include => ['/usr/include'];
print Dumper($c->configure);
Which will print something like this:
$VAR1 = {
'Define' => [
'DEBUGGING',
'FOO=123'
],
'StdCVersion' => 199901,
'ByteOrder' => 'LittleEndian',
'LongSize' => 4,
'IntSize' => 4,
'HostedC' => 1,
'ShortSize' => 2,
'HasMacroVAARGS' => 1,
'Assert' => [],
'UnsignedChars' => 0,
'DoubleSize' => 8,
'CharSize' => 1,
'EnumType' => 'Integer',
'PointerSize' => 4,
'EnumSize' => 4,
'DisabledKeywords' => [],
'FloatSize' => 4,
'Alignment' => 1,
'LongLongSize' => 8,
'LongDoubleSize' => 12,
'KeywordMap' => {},
'Include' => [
'/usr/include'
],
'HasCPPComments' => 1,
'Bitfields' => {
'Engine' => 'Generic'
},
'UnsignedBitfields' => 0,
'Warnings' => 0,
'CompoundAlignment' => 1,
'OrderMembers' => 0
};
Since you may not always want to write a "configure" call when you only want to
change a single configuration item, you can use any configuration option name as a
method name, like:
$c->ByteOrder('LittleEndian') if $c->IntSize < 4;
(Yes, the example doesn't make very much sense... ;-)
However, you should keep in mind that configuration methods that can take lists
(namely "Include", "Define" and "Assert", but not "DisabledKeywords") may behave
slightly different than their "configure" equivalent. If you pass these methods a
single argument that is an array reference, the current list will be replaced by
the new one, which is just the behaviour of the corresponding "configure" call.
So the following are equivalent:
$c->configure(Define => ['foo', 'bar=123']);
$c->Define(['foo', 'bar=123']);
But if you pass a list of strings instead of an array reference (which cannot be
done when using "configure"), the new list items are appended to the current list,
so
$c = new Convert::Binary::C Include => ['/include'];
$c->Include('/usr/include', '/usr/local/include');
print Dumper($c->Include);
$c->Include(['/usr/local/include']);
print Dumper($c->Include);
will first print all three include paths, but finally only "/usr/local/include"
will be configured:
$VAR1 = [
'/include',
'/usr/include',
'/usr/local/include'
];
$VAR1 = [
'/usr/local/include'
];
Furthermore, configuration methods can be chained together, as they return a
reference to their object if called as a set method. So, if you like, you can
configure your object like this:
$c = Convert::Binary::C->new(IntSize => 4)
->Define(qw( __DEBUG__ DB_LEVEL=3 ))
->ByteOrder('BigEndian');
$c->configure(EnumType => 'Both', Alignment => 4)
->Include('/usr/include', '/usr/local/include');
In the example above, "qw( ... )" is the word list quoting operator. It returns a
list of all non-whitespace sequences, and is especially useful for configuring
preprocessor defines or assertions. The following assignments are equivalent:
@array = ('one', 'two', 'three');
@array = qw(one two three);
You can configure the following options. Unknown options, as well as invalid
values for an option, will cause the object to throw exceptions.
"IntSize" => 0 | 1 | 2 | 4 | 8
Set the number of bytes that are occupied by an integer. This is in most cases
2 or 4. If you set it to zero, the size of an integer on the host system will
be used. This is also the default unless overridden by "CBC_DEFAULT_INT_SIZE"
at compile time.
"CharSize" => 0 | 1 | 2 | 4 | 8
Set the number of bytes that are occupied by a "char". This rarely needs to
be changed, except for some platforms that don't care about bytes, for example
DSPs. If you set this to zero, the size of a "char" on the host system will
be used. This is also the default unless overridden by "CBC_DEFAULT_CHAR_SIZE"
at compile time.
"ShortSize" => 0 | 1 | 2 | 4 | 8
Set the number of bytes that are occupied by a short integer. Although
integers explicitly declared as "short" should be always 16 bit, there are
compilers that make a short 8 bit wide. If you set it to zero, the size of a
short integer on the host system will be used. This is also the default unless
overridden by "CBC_DEFAULT_SHORT_SIZE" at compile time.
"LongSize" => 0 | 1 | 2 | 4 | 8
Set the number of bytes that are occupied by a long integer. If set to zero,
the size of a long integer on the host system will be used. This is also the
default unless overridden by "CBC_DEFAULT_LONG_SIZE" at compile time.
"LongLongSize" => 0 | 1 | 2 | 4 | 8
Set the number of bytes that are occupied by a long long integer. If set to
zero, the size of a long long integer on the host system, or 8, will be used.
This is also the default unless overridden by "CBC_DEFAULT_LONG_LONG_SIZE" at
compile time.
"FloatSize" => 0 | 1 | 2 | 4 | 8 | 12 | 16
Set the number of bytes that are occupied by a single precision floating point
value. If you set it to zero, the size of a "float" on the host system will
be used. This is also the default unless overridden by
"CBC_DEFAULT_FLOAT_SIZE" at compile time. For details on floating point
support, see "FLOATING POINT VALUES".
"DoubleSize" => 0 | 1 | 2 | 4 | 8 | 12 | 16
Set the number of bytes that are occupied by a double precision floating point
value. If you set it to zero, the size of a "double" on the host system will
be used. This is also the default unless overridden by
"CBC_DEFAULT_DOUBLE_SIZE" at compile time. For details on floating point
support, see "FLOATING POINT VALUES".
"LongDoubleSize" => 0 | 1 | 2 | 4 | 8 | 12 | 16
Set the number of bytes that are occupied by a double precision floating point
value. If you set it to zero, the size of a "long double" on the host system,
or 12 will be used. This is also the default unless overridden by
"CBC_DEFAULT_LONG_DOUBLE_SIZE" at compile time. For details on floating point
support, see "FLOATING POINT VALUES".
"PointerSize" => 0 | 1 | 2 | 4 | 8
Set the number of bytes that are occupied by a pointer. This is in most cases
2 or 4. If you set it to zero, the size of a pointer on the host system will
be used. This is also the default unless overridden by "CBC_DEFAULT_PTR_SIZE"
at compile time.
"EnumSize" => -1 | 0 | 1 | 2 | 4 | 8
Set the number of bytes that are occupied by an enumeration type. On most
systems, this is equal to the size of an integer, which is also the default.
However, for some compilers, the size of an enumeration type depends on the
size occupied by the largest enumerator. So the size may vary between 1 and 8.
If you have
enum foo {
ONE = 100, TWO = 200
};
this will occupy one byte because the enum can be represented as an unsigned
one-byte value. However,
enum foo {
ONE = -100, TWO = 200
};
will occupy two bytes, because the -100 forces the type to be signed, and 200
doesn't fit into a signed one-byte value. Therefore, the type used is a
signed two-byte value. If this is the behaviour you need, set the EnumSize to
0.
Some compilers try to follow this strategy, but don't care whether the
enumeration has signed values or not. They always declare an enum as signed.
On such a compiler, given
enum one { ONE = -100, TWO = 100 };
enum two { ONE = 100, TWO = 200 };
enum "one" will occupy only one byte, while enum "two" will occupy two bytes,
even though it could be represented by a unsigned one-byte value. If this is
the behaviour of your compiler, set EnumSize to "-1".
"Alignment" => 0 | 1 | 2 | 4 | 8 | 16
Set the struct member alignment. This option controls where padding bytes are
inserted between struct members. It globally sets the alignment for all
structs/unions. However, this can be overridden from within the source code
with the common "pack" pragma as explained in "Supported pragma directives".
The default alignment is 1, which means no padding bytes are inserted. A
setting of 0 means native alignment, i.e. the alignment of the system that
Convert::Binary::C has been compiled on. You can determine the native
properties using the "native" function.
The "Alignment" option is similar to the "-Zp[n]" option of the Intel
compiler. It globally specifies the maximum boundary to which struct members
are aligned. Consider the following structure and the sizes of "char",
"short", "long" and "double" being 1, 2, 4 and 8, respectively.
struct align {
char a;
short b, c;
long d;
double e;
};
With an alignment of 1 (the default), the struct members would be packed
tightly:
0 1 2 3 4 5 6 7 8 9 10 11 12
+---+---+---+---+---+---+---+---+---+---+---+---+
| a | b | c | d | ...
+---+---+---+---+---+---+---+---+---+---+---+---+
12 13 14 15 16 17
+---+---+---+---+---+
... e |
+---+---+---+---+---+
With an alignment of 2, the struct members larger than one byte would be
aligned to 2-byte boundaries, which results in a single padding byte between
"a" and "b".
0 1 2 3 4 5 6 7 8 9 10 11 12
+---+---+---+---+---+---+---+---+---+---+---+---+
| a | * | b | c | d | ...
+---+---+---+---+---+---+---+---+---+---+---+---+
12 13 14 15 16 17 18
+---+---+---+---+---+---+
... e |
+---+---+---+---+---+---+
With an alignment of 4, the struct members of size 2 would be aligned to
2-byte boundaries and larger struct members would be aligned to 4-byte
boundaries:
0 1 2 3 4 5 6 7 8 9 10 11 12
+---+---+---+---+---+---+---+---+---+---+---+---+
| a | * | b | c | * | * | d | ...
+---+---+---+---+---+---+---+---+---+---+---+---+
12 13 14 15 16 17 18 19 20
+---+---+---+---+---+---+---+---+
... | e |
+---+---+---+---+---+---+---+---+
This layout of the struct members allows the compiler to generate optimized
code because aligned members can be accessed more easily by the underlying
architecture.
Finally, setting the alignment to 8 will align "double"s to 8-byte boundaries:
0 1 2 3 4 5 6 7 8 9 10 11 12
+---+---+---+---+---+---+---+---+---+---+---+---+
| a | * | b | c | * | * | d | ...
+---+---+---+---+---+---+---+---+---+---+---+---+
12 13 14 15 16 17 18 19 20 21 22 23 24
+---+---+---+---+---+---+---+---+---+---+---+---+
... | * | * | * | * | e |
+---+---+---+---+---+---+---+---+---+---+---+---+
Further increasing the alignment does not alter the layout of our structure,
as only members larger that 8 bytes would be affected.
The alignment of a structure depends on its largest member and on the setting
of the "Alignment" option. With "Alignment" set to 2, a structure holding a
"long" would be aligned to a 2-byte boundary, while a structure containing
only "char"s would have no alignment restrictions. (Unfortunately, that's not
the whole story. See the "CompoundAlignment" option for details.)
Here's another example. Assuming 8-byte alignment, the following two structs
will both have a size of 16 bytes:
struct one {
char c;
double d;
};
struct two {
double d;
char c;
};
This is clear for "struct one", because the member "d" has to be aligned to an
8-byte boundary, and thus 7 padding bytes are inserted after "c". But for
"struct two", the padding bytes are inserted at the end of the structure,
which doesn't make much sense immediately. However, it makes perfect sense if
you think about an array of "struct two". Each "double" has to be aligned to
an 8-byte boundary, an thus each array element would have to occupy 16 bytes.
With that in mind, it would be strange if a "struct two" variable would have a
different size. And it would make the widely used construct
struct two array[] = { {1.0, 0}, {2.0, 1} };
int elements = sizeof(array) / sizeof(struct two);
impossible.
The alignment behaviour described here seems to be common for all compilers.
However, not all compilers have an option to configure their default
alignment.
"CompoundAlignment" => 0 | 1 | 2 | 4 | 8 | 16
Usually, the alignment of a compound (i.e. a "struct" or a "union") depends
only on its largest member and on the setting of the "Alignment" option. There
are, however, architectures and compilers where compounds can have different
alignment constraints.
For most platforms and compilers, the alignment constraint for compounds is 1
byte. That is, on most platforms
struct onebyte {
char byte;
};
will have an alignment of 1 and also a size of 1. But if you take an ARM
architecture, the above "struct onebyte" will have an alignment of 4, and thus
also a size of 4.
You can configure this by setting "CompoundAlignment" to 4. This will ensure
that the alignment of compounds is always 4.
Setting "CompoundAlignment" to 0 means native compound alignment, i.e. the
compound alignment of the system that Convert::Binary::C has been compiled on.
You can determine the native properties using the "native" function.
There are also compilers for certain platforms that allow you to adjust the
compound alignment. If you're not aware of the fact that your
compiler/architecture has a compound alignment other than 1, strange things
can happen. If, for example, the compound alignment is 2 and you have
something like
typedef unsigned char U8;
struct msg_head {
U8 cmd;
struct {
U8 hi;
U8 low;
} crc16;
U8 len;
};
there will be one padding byte inserted before the embedded "crc16" struct and
after the "len" member, which is most probably not what was intended:
0 1 2 3 4 5 6
+-----+-----+-----+-----+-----+-----+
| cmd | * | hi | low | len | * |
+-----+-----+-----+-----+-----+-----+
Note that both "#pragma pack" and the "Alignment" option can override
"CompoundAlignment". If you set "CompoundAlignment" to 4, but "Alignment" to
2, compounds will actually be aligned on 2-byte boundaries.
"ByteOrder" => 'BigEndian' | 'LittleEndian'
Set the byte order for integers larger than a single byte. Little endian
(Intel, least significant byte first) and big endian (Motorola, most
significant byte first) byte order are supported. The default byte order is
the same as the byte order of the host system unless overridden by
"CBC_DEFAULT_BYTEORDER" at compile time.
"EnumType" => 'Integer' | 'String' | 'Both'
This option controls the type that enumeration constants will have in data
structures returned by the "unpack" method. If you have the following
definitions:
typedef enum {
SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, SATURDAY
} Weekday;
typedef enum {
JANUARY, FEBRUARY, MARCH, APRIL, MAY, JUNE, JULY,
AUGUST, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER
} Month;
typedef struct {
int year;
Month month;
int day;
Weekday weekday;
} Date;
and a byte string that holds a packed Date struct, then you'll get the
following results from a call to the "unpack" method.
"Integer"
Enumeration constants are returned as plain integers. This is fast, but
may be not very useful. It is also the default.
$date = {
'weekday' => 1,
'month' => 0,
'day' => 7,
'year' => 2002
};
"String"
Enumeration constants are returned as strings. This will create a string
constant for every unpacked enumeration constant and thus consumes more
time and memory. However, the result may be more useful.
$date = {
'weekday' => 'MONDAY',
'month' => 'JANUARY',
'day' => 7,
'year' => 2002
};
"Both"
Enumeration constants are returned as double typed scalars. If evaluated
in string context, the enumeration constant will be a string, if evaluated
in numeric context, the enumeration constant will be an integer.
$date = $c->EnumType('Both')->unpack('Date', $binary);
printf "Weekday = %s (%d)\n\n", $date->{weekday},
$date->{weekday};
if ($date->{month} == 0) {
print "It's $date->{month}, happy new year!\n\n";
}
print Dumper($date);
This will print:
Weekday = MONDAY (1)
It's JANUARY, happy new year!
$VAR1 = {
'weekday' => 'MONDAY',
'month' => 'JANUARY',
'day' => 7,
'year' => 2002
};
"DisabledKeywords" => [ KEYWORDS ]
This option allows you to selectively deactivate certain keywords in the C
parser. Some C compilers don't have the complete ANSI keyword set, i.e. they
don't recognize the keywords "const" or "void", for example. If you do
typedef int void;
on such a compiler, this will usually be ok. But if you parse this with an
ANSI compiler, it will be a syntax error. To parse the above code correctly,
you have to disable the "void" keyword in the Convert::Binary::C parser:
$c->DisabledKeywords([qw( void )]);
By default, the Convert::Binary::C parser will recognize the keywords "inline"
and "restrict". If your compiler doesn't have these new keywords, it usually
doesn't matter. Only if you're using the keywords as identifiers, like in
typedef struct inline {
int a, b;
} restrict;
you'll have to disable these ISO-C99 keywords:
$c->DisabledKeywords([qw( inline restrict )]);
The parser allows you to disable the following keywords:
asm
auto
const
double
enum
extern
float
inline
long
register
restrict
short
signed
static
unsigned
void
volatile
"KeywordMap" => { KEYWORD => TOKEN, ... }
This option allows you to add new keywords to the parser. These new keywords
can either be mapped to existing tokens or simply ignored. For example, recent
versions of the GNU compiler recognize the keywords "__signed__" and
"__extension__". The first one obviously is a synonym for "signed", while the
second one is only a marker for a language extension.
Using the preprocessor, you could of course do the following:
$c->Define(qw( __signed__=signed __extension__= ));
However, the preprocessor symbols could be undefined or redefined in the code,
and
#ifdef __signed__
# undef __signed__
#endif
typedef __extension__ __signed__ long long s_quad;
would generate a parse error, because "__signed__" is an unexpected
identifier.
Instead of utilizing the preprocessor, you'll have to create mappings for the
new keywords directly in the parser using "KeywordMap". In the above example,
you want to map "__signed__" to the built-in C keyword "signed" and ignore
"__extension__". This could be done with the following code:
$c->KeywordMap({ __signed__ => 'signed',
__extension__ => undef });
You can specify any valid identifier as hash key, and either a valid C keyword
or "undef" as hash value. Having configured the object that way, you could
parse even
#ifdef __signed__
# undef __signed__
#endif
typedef __extension__ __signed__ long long s_quad;
without problems.
Note that "KeywordMap" and "DisabledKeywords" perfectly work together. You
could, for example, disable the "signed" keyword, but still have "__signed__"
mapped to the original "signed" token:
$c->configure(DisabledKeywords => [ 'signed' ],
KeywordMap => { __signed__ => 'signed' });
This would allow you to define
typedef __signed__ long signed;
which would normally be a syntax error because "signed" cannot be used as an
identifier.
"UnsignedChars" => 0 | 1
Use this boolean option if you want characters to be unsigned if specified
without an explicit "signed" or "unsigned" type specifier. By default,
characters are signed.
"UnsignedBitfields" => 0 | 1
Use this boolean option if you want bitfields to be unsigned if specified
without an explicit "signed" or "unsigned" type specifier. By default,
bitfields are signed.
"Warnings" => 0 | 1
Use this boolean option if you want warnings to be issued during the parsing
of source code. Currently, warnings are only reported by the preprocessor, so
don't expect the output to cover everything.
By default, warnings are turned off and only errors will be reported. However,
even these errors are turned off if you run without the "-w" flag.
"HasCPPComments" => 0 | 1
Use this option to turn C++ comments on or off. By default, C++ comments are
enabled. Disabling C++ comments may be necessary if your code includes strange
things like:
one = 4 //* <- divide */ 4;
two = 2;
With C++ comments, the above will be interpreted as
one = 4
two = 2;
which will obviously be a syntax error, but without C++ comments, it will be
interpreted as
one = 4 / 4;
two = 2;
which is correct.
"HasMacroVAARGS" => 0 | 1
Use this option to turn the "__VA_ARGS__" macro expansion on or off. If this
is enabled (which is the default), you can use variable length argument lists
in your preprocessor macros.
#define DEBUG( ... ) fprintf( stderr, __VA_ARGS__ )
There's normally no reason to turn that feature off.
"StdCVersion" => undef | INTEGER
Use this option to change the value of the preprocessor's predefined
"__STDC_VERSION__" macro. When set to "undef", the macro will not be defined.
"HostedC" => undef | 0 | 1
Use this option to change the value of the preprocessor's predefined
"__STDC_HOSTED__" macro. When set to "undef", the macro will not be defined.
"Include" => [ INCLUDES ]
Use this option to set the include path for the internal preprocessor. The
option value is a reference to an array of strings, each string holding a
directory that should be searched for includes.
"Define" => [ DEFINES ]
Use this option to define symbols in the preprocessor. The option value is,
again, a reference to an array of strings. Each string can be either just a
symbol or an assignment to a symbol. This is completely equivalent to what the
"-D" option does for most preprocessors.
The following will define the symbol "FOO" and define "BAR" to be 12345:
$c->configure(Define => [qw( FOO BAR=12345 )]);
"Assert" => [ ASSERTIONS ]
Use this option to make assertions in the preprocessor. If you don't know
what assertions are, don't be concerned, since they're deprecated anyway. They
are, however, used in some system's include files. The value is an array
reference, just like for the macro definitions. Only the way the assertions
are defined is a bit different and mimics the way they are defined with the
"#assert" directive:
$c->configure(Assert => ['foo(bar)']);
"OrderMembers" => 0 | 1
When using "unpack" on compounds and iterating over the returned hash, the
order of the compound members is generally not preserved due to the nature of
hash tables. It is not even guaranteed that the order is the same between
different runs of the same program. This can be very annoying if you simply
use to dump your data structures and the compound members always show up in a
different order.
By setting "OrderMembers" to a non-zero value, all hashes returned by "unpack"
are tied to a class that preserves the order of the hash keys. This way, all
compound members will be returned in the correct order just as they are
defined in your C code.
use Convert::Binary::C;
use Data::Dumper;
$c = Convert::Binary::C->new->parse(<<'ENDC');
struct test {
char one;
char two;
struct {
char never;
char change;
char this;
char order;
} three;
char four;
};
ENDC
$data = "Convert";
$u1 = $c->unpack('test', $data);
$c->OrderMembers(1);
$u2 = $c->unpack('test', $data);
print Data::Dumper->Dump([$u1, $u2], [qw(u1 u2)]);
This will print something like:
$u1 = {
'three' => {
'change' => 118,
'order' => 114,
'this' => 101,
'never' => 110
},
'one' => 67,
'two' => 111,
'four' => 116
};
$u2 = {
'one' => 67,
'two' => 111,
'three' => {
'never' => 110,
'change' => 118,
'this' => 101,
'order' => 114
},
'four' => 116
};
To be able to use this option, you have to install either the
Tie::Hash::Indexed or the Tie::IxHash module. If both are installed,
Convert::Binary::C will give preference to Tie::Hash::Indexed because it's
faster.
When using this option, you should keep in mind that tied hashes are
significantly slower and consume more memory than ordinary hashes, even when
the class they're tied to is implemented efficiently. So don't turn this
option on if you don't have to.
You can also influence hash member ordering by using the "CBC_ORDER_MEMBERS"
environment variable.
"Bitfields" => { OPTION => VALUE, ... }
Use this option to specify and configure a bitfield layouting engine. You can
choose an engine by passing its name to the "Engine" option, like:
$c->configure(Bitfields => { Engine => 'Generic' });
Each engine can have its own set of options, although currently none of them
does.
You can choose between the following bitfield engines:
"Generic"
This engine implements the behaviour of most UNIX C compilers, including
GCC. It does not handle packed bitfields yet.
"Microsoft"
This engine implements the behaviour of Microsoft's "cl" compiler. It
should be fairly complete and can handle packed bitfields.
"Simple"
This engine is only used for testing the bitfield infrastructure in
Convert::Binary::C. There's usually no reason to use it.
You can reconfigure all options even after you have parsed some code. The changes
will be applied to the already parsed definitions. This works as long as array
lengths are not affected by the changes. If you have Alignment and IntSize set to
4 and parse code like this
typedef struct {
char abc;
int day;
} foo;
struct bar {
foo zap[2*sizeof(foo)];
};
the array "zap" in "struct bar" will obviously have 16 elements. If you
reconfigure the alignment to 1 now, the size of "foo" is now 5 instead of 8. While
the alignment is adjusted correctly, the number of elements in array "zap" will
still be 16 and will not be changed to 10.
parse
"parse" CODE
Parses a string of valid C code. All enumeration, compound and type definitions
are extracted. You can call the "parse" and "parse_file" methods as often as you
like to add further definitions to the Convert::Binary::C object.
"parse" will throw an exception if an error occurs. On success, the method
returns a reference to its object.
See "Parsing C code" for an example.
parse_file
"parse_file" FILE
Parses a C source file. All enumeration, compound and type definitions are
extracted. You can call the "parse" and "parse_file" methods as often as you like
to add further definitions to the Convert::Binary::C object.
"parse_file" will search the include path given via the "Include" option for the
file if it cannot find it in the current directory.
"parse_file" will throw an exception if an error occurs. On success, the method
returns a reference to its object.
See "Parsing C code" for an example.
When calling "parse" or "parse_file" multiple times, you may use types previously
defined, but you are not allowed to redefine types. The state of the preprocessor
is also saved, so you may also use defines from a previous parse. This works only
as long as the preprocessor is not reset. See "Preprocessor configuration" for
details.
When you're parsing C source files instead of C header files, note that local
definitions are ignored. This means that type definitions hidden within functions
will not be recognized by Convert::Binary::C. This is necessary because different
functions (even different blocks within the same function) can define types with
the same name:
void my_func(int i)
{
if (i < 10)
{
enum digit { ONE, TWO, THREE } x = ONE;
printf("%d, %d\n", i, x);
}
else
{
enum digit { THREE, TWO, ONE } x = ONE;
printf("%d, %d\n", i, x);
}
}
The above is a valid piece of C code, but it's not possible for Convert::Binary::C
to distinguish between the different definitions of "enum digit", as they're only
defined locally within the corresponding block.
clean
"clean" Clears all information that has been collected during previous calls to "parse" or
"parse_file". You can use this method if you want to parse some entirely
different code, but with the same configuration.
The "clean" method returns a reference to its object.
clone
"clone" Makes the object return an exact independent copy of itself.
$c = new Convert::Binary::C Include => ['/usr/include'];
$c->parse_file('definitions.c');
$clone = $c->clone;
The above code is technically equivalent (Mostly. Actually, using "sourcify" and
"parse" might alter the order of the parsed data, which would make methods such as
"compound" return the definitions in a different order.) to:
$c = new Convert::Binary::C Include => ['/usr/include'];
$c->parse_file('definitions.c');
$clone = new Convert::Binary::C %{$c->configure};
$clone->parse($c->sourcify);
Using "clone" is just a lot faster.
def
"def" NAME
"def" TYPE
If you need to know if a definition for a certain type name exists, use this
method. You pass it the name of an enum, struct, union or typedef, and it will
return a non-empty string being either "enum", "struct", "union", or "typedef" if
there's a definition for the type in question, an empty string if there's no such
definition, or "undef" if the name is completely unknown. If the type can be
interpreted as a basic type, "basic" will be returned.
If you pass in a TYPE, the output will be slightly different. If the specified
member exists, the "def" method will return "member". If the member doesn't exist,
or if the type cannot have members, the empty string will be returned. Again, if
the name of the type is completely unknown, "undef" will be returned. This may be
useful if you want to check if a certain member exists within a compound, for
example.
use Convert::Binary::C;
my $c = Convert::Binary::C->new->parse(<<'ENDC');
typedef struct __not not;
typedef struct __not *ptr;
struct foo {
enum bar *xxx;
};
typedef int quad[4];
ENDC
for my $type (qw( not ptr foo bar xxx foo.xxx foo.abc xxx.yyy
quad quad[3] quad[5] quad[-3] short[1] ),
'unsigned long')
{
my $def = $c->def($type);
printf "%-14s => %s\n",
$type, defined $def ? "'$def'" : 'undef';
}
The following would be returned by the "def" method:
not => ''
ptr => 'typedef'
foo => 'struct'
bar => ''
xxx => undef
foo.xxx => 'member'
foo.abc => ''
xxx.yyy => undef
quad => 'typedef'
quad[3] => 'member'
quad[5] => 'member'
quad[-3] => 'member'
short[1] => undef
unsigned long => 'basic'
So, if "def" returns a non-empty string, you can safely use any other method with
that type's name or with that member expression.
Concerning arrays, note that the index into an array doesn't need to be within the
bounds of the array's definition, just like in C. In the above example, "quad[5]"
and "quad[-3]" are valid members of the "quad" array, even though it is declared
to have only four elements.
In cases where the typedef namespace overlaps with the namespace of
enums/structs/unions, the "def" method will give preference to the typedef and
will thus return the string "typedef". You could however force interpretation as
an enum, struct or union by putting "enum", "struct" or "union" in front of the
type's name.
defined
"defined" MACRO
You can use the "defined" method to find out if a certain macro is defined, just
like you would use the "defined" operator of the preprocessor. For example, the
following code
use Convert::Binary::C;
my $c = Convert::Binary::C->new->parse(<<'ENDC');
#define ADD(a, b) ((a) + (b))
#if 1
# define DEFINED
#else
# define UNDEFINED
#endif
ENDC
for my $macro (qw( ADD DEFINED UNDEFINED )) {
my $not = $c->defined($macro) ? '' : ' not';
print "Macro '$macro' is$not defined.\n";
}
would print:
Macro 'ADD' is defined.
Macro 'DEFINED' is defined.
Macro 'UNDEFINED' is not defined.
You have to keep in mind that this works only as long as the preprocessor is not
reset. See "Preprocessor configuration" for details.
pack
"pack" TYPE
"pack" TYPE, DATA
"pack" TYPE, DATA, STRING
Use this method to pack a complex data structure into a binary string according to
a type definition that has been previously parsed. DATA must be a scalar matching
the type definition. C structures and unions are represented by references to Perl
hashes, C arrays by references to Perl arrays.
use Convert::Binary::C;
use Data::Dumper;
use Data::Hexdumper;
$c = Convert::Binary::C->new( ByteOrder => 'BigEndian'
, LongSize => 4
, ShortSize => 2
)
->parse(<<'ENDC');
struct test {
char ary[3];
union {
short word[2];
long quad;
} uni;
};
ENDC
Hashes don't have to contain a key for each compound member and arrays may be
truncated:
$binary = $c->pack('test', { ary => [1, 2], uni => { quad => 42 } });
Elements not defined in the Perl data structure will be set to zero in the packed
byte string. If you pass "undef" as or simply omit the second parameter, the whole
string will be initialized with zero bytes. On success, the packed byte string is
returned.
print hexdump(data => $binary);
The above code would print:
0x0000 : 01 02 00 00 00 00 2A : ......*
You could also use "unpack" and dump the data structure.
$unpacked = $c->unpack('test', $binary);
print Data::Dumper->Dump([$unpacked], ['unpacked']);
This would print:
$unpacked = {
'uni' => {
'word' => [
0,
42
],
'quad' => 42
},
'ary' => [
1,
2,
0
]
};
If TYPE refers to a compound object, you may pack any member of that compound
object. Simply add a member expression to the type name, just as you would access
the member in C:
$array = $c->pack('test.ary', [1, 2, 3]);
print hexdump(data => $array);
$value = $c->pack('test.uni.word[1]', 2);
print hexdump(data => $value);
This would give you:
0x0000 : 01 02 03 : ...
0x0000 : 00 02 : ..
Call "pack" with the optional STRING argument if you want to use an existing
binary string to insert the data. If called in a void context, "pack" will
directly modify the string you passed as the third argument. Otherwise, a copy of
the string is created, and "pack" will modify and return the copy, so the original
string will remain unchanged.
The 3-argument version may be useful if you want to change only a few members of a
complex data structure without having to "unpack" everything, change the members,
and then "pack" again (which could waste lots of memory and CPU cycles). So,
instead of doing something like
$test = $c->unpack('test', $binary);
$test->{uni}{quad} = 4711;
$new = $c->pack('test', $test);
to change the "uni.quad" member of $packed, you could simply do either
$new = $c->pack('test', { uni => { quad => 4711 } }, $binary);
or
$c->pack('test', { uni => { quad => 4711 } }, $binary);
while the latter would directly modify $packed. Besides this code being a lot
shorter (and perhaps even more readable), it can be significantly faster if you're
dealing with really big data blocks.
If the length of the input string is less than the size required by the type, the
string (or its copy) is extended and the extended part is initialized to zero. If
the length is more than the size required by the type, the string is kept at that
length, and also a copy would be an exact copy of that string.
$too_short = pack "C*", (1 .. 4);
$too_long = pack "C*", (1 .. 20);
$c->pack('test', { uni => { quad => 0x4711 } }, $too_short);
print "too_short:\n", hexdump(data => $too_short);
$copy = $c->pack('test', { uni => { quad => 0x4711 } }, $too_long);
print "\ncopy:\n", hexdump(data => $copy);
This would print:
too_short:
0x0000 : 01 02 03 00 00 47 11 : .....G.
copy:
0x0000 : 01 02 03 00 00 47 11 08 09 0A 0B 0C 0D 0E 0F 10 : .....G..........
0x0010 : 11 12 13 14 : ....
unpack
"unpack" TYPE, STRING
Use this method to unpack a binary string and create an arbitrarily complex Perl
data structure based on a previously parsed type definition.
use Convert::Binary::C;
use Data::Dumper;
$c = Convert::Binary::C->new( ByteOrder => 'BigEndian'
, LongSize => 4
, ShortSize => 2
)
->parse( <<'ENDC' );
struct test {
char ary[3];
union {
short word[2];
long *quad;
} uni;
};
ENDC
# Generate some binary dummy data
$binary = pack "C*", 1 .. $c->sizeof('test');
On failure, e.g. if the specified type cannot be found, the method will throw an
exception. On success, a reference to a complex Perl data structure is returned,
which can directly be dumped using the Data::Dumper module:
$unpacked = $c->unpack('test', $binary);
print Dumper($unpacked);
This would print:
$VAR1 = {
'uni' => {
'word' => [
1029,
1543
],
'quad' => 67438087
},
'ary' => [
1,
2,
3
]
};
If TYPE refers to a compound object, you may unpack any member of that compound
object. Simply add a member expression to the type name, just as you would access
the member in C:
$binary2 = substr $binary, $c->offsetof('test', 'uni.word');
$unpack1 = $unpacked->{uni}{word};
$unpack2 = $c->unpack('test.uni.word', $binary2);
print Data::Dumper->Dump([$unpack1, $unpack2], [qw(unpack1 unpack2)]);
You will find that the output is exactly the same for both $unpack1 and $unpack2:
$unpack1 = [
1029,
1543
];
$unpack2 = [
1029,
1543
];
When "unpack" is called in list context, it will unpack as many elements as
possible from STRING, including zero if STRING is not long enough.
initializer
"initializer" TYPE
"initializer" TYPE, DATA
The "initializer" method can be used retrieve an initializer string for a certain
TYPE. This can be useful if you have to initialize only a couple of members in a
huge compound type or if you simply want to generate initializers automatically.
struct date {
unsigned year : 12;
unsigned month: 4;
unsigned day : 5;
unsigned hour : 5;
unsigned min : 6;
};
typedef struct {
enum { DATE, QWORD } type;
short number;
union {
struct date date;
unsigned long qword;
} choice;
} data;
Given the above code has been parsed
$init = $c->initializer('data');
print "data x = $init;\n";
would print the following:
data x = {
0,
0,
{
{
0,
0,
0,
0,
0
}
}
};
You could directly put that into a C program, although it probably isn't very
useful yet. It becomes more useful if you actually specify how you want to
initialize the type:
$data = {
type => 'QWORD',
choice => {
date => { month => 12, day => 24 },
qword => 4711,
},
stuff => 'yes?',
};
$init = $c->initializer('data', $data);
print "data x = $init;\n";
This would print the following:
data x = {
QWORD,
0,
{
{
0,
12,
24,
0,
0
}
}
};
As only the first member of a "union" can be initialized, "choice.qword" is
ignored. You will not be warned about the fact that you probably tried to
initialize a member other than the first. This is considered a feature, because it
allows you to use "unpack" to generate the initializer data:
$data = $c->unpack('data', $binary);
$init = $c->initializer('data', $data);
Since "unpack" unpacks all union members, you would otherwise have to delete all
but the first one previous to feeding it into "initializer".
Also, "stuff" is ignored, because it actually isn't a member of "data". You won't
be warned about that either.
sizeof
"sizeof" TYPE
This method will return the size of a C type in bytes. If it cannot find the
type, it will throw an exception.
If the type defines some kind of compound object, you may ask for the size of a
member of that compound object:
$size = $c->sizeof('test.uni.word[1]');
This would set $size to 2.
typeof
"typeof" TYPE
This method will return the type of a C member. While this only makes sense for
compound types, it's legal to also use it for non-compound types. If it cannot
find the type, it will throw an exception.
The "typeof" method can be used on any valid member, even on arrays or unnamed
types. It will always return a string that holds the name (or in case of unnamed
types only the class) of the type, optionally followed by a '*' character to
indicate it's a pointer type, and optionally followed by one or more array
dimensions if it's an array type. If the type is a bitfield, the type name is
followed by a colon and the number of bits.
struct test {
char ary[3];
union {
short word[2];
long *quad;
} uni;
struct {
unsigned short six:6;
unsigned short ten:10;
} bits;
};
Given the above C code has been parsed, calls to "typeof" would return the
following values:
$c->typeof('test') => 'struct test'
$c->typeof('test.ary') => 'char [3]'
$c->typeof('test.uni') => 'union'
$c->typeof('test.uni.quad') => 'long *'
$c->typeof('test.uni.word') => 'short [2]'
$c->typeof('test.uni.word[1]') => 'short'
$c->typeof('test.bits') => 'struct'
$c->typeof('test.bits.six') => 'unsigned short :6'
$c->typeof('test.bits.ten') => 'unsigned short :10'
offsetof
"offsetof" TYPE, MEMBER
You can use "offsetof" just like the C macro of same denominator. It will simply
return the offset (in bytes) of MEMBER relative to TYPE.
use Convert::Binary::C;
$c = Convert::Binary::C->new( Alignment => 4
, LongSize => 4
, PointerSize => 4
)
->parse(<<'ENDC');
typedef struct {
char abc;
long day;
int *ptr;
} week;
struct test {
week zap[8];
};
ENDC
@args = (
['test', 'zap[5].day' ],
['test.zap[2]', 'day' ],
['test', 'zap[5].day+1'],
['test', 'zap[-3].ptr' ],
);
for (@args) {
my $offset = eval { $c->offsetof(@$_) };
printf "\$c->offsetof('%s', '%s') => $offset\n", @$_;
}
The final loop will print:
$c->offsetof('test', 'zap[5].day') => 64
$c->offsetof('test.zap[2]', 'day') => 4
$c->offsetof('test', 'zap[5].day+1') => 65
$c->offsetof('test', 'zap[-3].ptr') => -28
• The first iteration simply shows that the offset of "zap[5].day" is 64 relative
to the beginning of "struct test".
• You may additionally specify a member for the type passed as the first argument,
as shown in the second iteration.
• The offset suffix is also supported by "offsetof", so the third iteration will
correctly print 65.
• The last iteration demonstrates that even out-of-bounds array indices are
handled correctly, just as they are handled in C.
Unlike the C macro, "offsetof" also works on array types.
$offset = $c->offsetof('test.zap', '[3].ptr+2');
print "offset = $offset";
This will print:
offset = 46
If TYPE is a compound, MEMBER may optionally be prefixed with a dot, so
printf "offset = %d\n", $c->offsetof('week', 'day');
printf "offset = %d\n", $c->offsetof('week', '.day');
are both equivalent and will print
offset = 4
offset = 4
This allows one to
• use the C macro style, without a leading dot, and
• directly use the output of the "member" method, which includes a leading dot for
compound types, as input for the MEMBER argument.
member
"member" TYPE
"member" TYPE, OFFSET
You can think of "member" as being the reverse of the "offsetof" method. However,
as this is more complex, there's no equivalent to "member" in the C language.
Usually this method is used if you want to retrieve the name of the member that is
located at a specific offset of a previously parsed type.
use Convert::Binary::C;
$c = Convert::Binary::C->new( Alignment => 4
, LongSize => 4
, PointerSize => 4
)
->parse(<<'ENDC');
typedef struct {
char abc;
long day;
int *ptr;
} week;
struct test {
week zap[8];
};
ENDC
for my $offset (24, 39, 69, 99) {
print "\$c->member('test', $offset)";
my $member = eval { $c->member('test', $offset) };
print $@ ? "\n exception: $@" : " => '$member'\n";
}
This will print:
$c->member('test', 24) => '.zap[2].abc'
$c->member('test', 39) => '.zap[3]+3'
$c->member('test', 69) => '.zap[5].ptr+1'
$c->member('test', 99)
exception: Offset 99 out of range (0 <= offset < 96)
• The output of the first iteration is obvious. The member "zap[2].abc" is located
at offset 24 of "struct test".
• In the second iteration, the offset points into a region of padding bytes and
thus no member of "week" can be named. Instead of a member name the offset
relative to "zap[3]" is appended.
• In the third iteration, the offset points to "zap[5].ptr". However,
"zap[5].ptr" is located at 68, not at 69, and thus the remaining offset of 1 is
also appended.
• The last iteration causes an exception because the offset of 99 is not valid for
"struct test" since the size of "struct test" is only 96. You might argue that
this is inconsistent, since "offsetof" can also handle out-of-bounds array
members. But as soon as you have more than one level of array nesting, there's
an infinite number of out-of-bounds members for a single given offset, so it
would be impossible to return a list of all members.
You can additionally specify a member for the type passed as the first argument:
$member = $c->member('test.zap[2]', 6);
print $member;
This will print:
.day+2
Like "offsetof", "member" also works on array types:
$member = $c->member('test.zap', 42);
print $member;
This will print:
[3].day+2
While the behaviour for "struct"s is quite obvious, the behaviour for "union"s is
rather tricky. As a single offset usually references more than one member of a
union, there are certain rules that the algorithm uses for determining the best
member.
• The first non-compound member that is referenced without an offset has the
highest priority.
• If no member is referenced without an offset, the first non-compound member that
is referenced with an offset will be returned.
• Otherwise the first padding region that is encountered will be taken.
As an example, given 4-byte-alignment and the union
union choice {
struct {
char color[2];
long size;
char taste;
} apple;
char grape[3];
struct {
long weight;
short price[3];
} melon;
};
the "member" method would return what is shown in the Member column of the
following table. The Type column shows the result of the "typeof" method when
passing the corresponding member.
Offset Member Type
--------------------------------------
0 .apple.color[0] 'char'
1 .apple.color[1] 'char'
2 .grape[2] 'char'
3 .melon.weight+3 'long'
4 .apple.size 'long'
5 .apple.size+1 'long'
6 .melon.price[1] 'short'
7 .apple.size+3 'long'
8 .apple.taste 'char'
9 .melon.price[2]+1 'short'
10 .apple+10 'struct'
11 .apple+11 'struct'
It's like having a stack of all the union members and looking through the stack
for the shiniest piece you can see. The beginning of a member (denoted by
uppercase letters) is always shinier than the rest of a member, while padding
regions (denoted by dashes) aren't shiny at all.
Offset 0 1 2 3 4 5 6 7 8 9 10 11
-------------------------------------------------------
apple (C) (C) - - (S) (s) s (s) (T) - (-) (-)
grape G G (G)
melon W w w (w) P p (P) p P (p) - -
If you look through that stack from top to bottom, you'll end up at the
parenthesized members.
Alternatively, if you're not only interested in the best member, you can call
"member" in list context, which makes it return all members referenced by the
given offset.
Offset Member Type
--------------------------------------
0 .apple.color[0] 'char'
.grape[0] 'char'
.melon.weight 'long'
1 .apple.color[1] 'char'
.grape[1] 'char'
.melon.weight+1 'long'
2 .grape[2] 'char'
.melon.weight+2 'long'
.apple+2 'struct'
3 .melon.weight+3 'long'
.apple+3 'struct'
4 .apple.size 'long'
.melon.price[0] 'short'
5 .apple.size+1 'long'
.melon.price[0]+1 'short'
6 .melon.price[1] 'short'
.apple.size+2 'long'
7 .apple.size+3 'long'
.melon.price[1]+1 'short'
8 .apple.taste 'char'
.melon.price[2] 'short'
9 .melon.price[2]+1 'short'
.apple+9 'struct'
10 .apple+10 'struct'
.melon+10 'struct'
11 .apple+11 'struct'
.melon+11 'struct'
The first member returned is always the best member. The other members are sorted
according to the rules given above. This means that members referenced without an
offset are followed by members referenced with an offset. Padding regions will be
at the end.
If OFFSET is not given in the method call, "member" will return a list of all
possible members of TYPE.
print "$_\n" for $c->member('choice');
This will print:
.apple.color[0]
.apple.color[1]
.apple.size
.apple.taste
.grape[0]
.grape[1]
.grape[2]
.melon.weight
.melon.price[0]
.melon.price[1]
.melon.price[2]
In scalar context, the number of possible members is returned.
tag
"tag" TYPE
"tag" TYPE, TAG
"tag" TYPE, TAG1 => VALUE1, TAG2 => VALUE2, ...
The "tag" method can be used to tag properties to a TYPE. It's a bit like having
"configure" for individual types.
See "USING TAGS" for an example.
Note that while you can tag whole types as well as compound members, it is not
possible to tag array members, i.e. you cannot treat, for example, "a[1]" and
"a[2]" differently.
Also note that in code like this
struct test {
int a;
struct {
int x;
} b, c;
};
if you tag "test.b.x", this will also tag "test.c.x" implicitly.
It is also possible to tag basic types if you really want to do that, for example:
$c->tag('int', Format => 'Binary');
To remove a tag from a type, you can either set that tag to "undef", for example
$c->tag('test', Hooks => undef);
or use "untag".
To see if a tag is attached to a type or to get the value of a tag, pass only the
type and tag name to "tag":
$c->tag('test.a', Format => 'Binary');
$hooks = $c->tag('test.a', 'Hooks');
$format = $c->tag('test.a', 'Format');
This will give you:
$hooks = undef;
$format = 'Binary';
To see which tags are attached to a type, pass only the type. The "tag" method
will now return a hash reference containing all tags attached to the type:
$tags = $c->tag('test.a');
This will give you:
$tags = {
'Format' => 'Binary'
};
"tag" will throw an exception if an error occurs. If called as a 'set' method, it
will return a reference to its object, allowing you to chain together consecutive
method calls.
Note that when a compound is inlined, tags attached to the inlined compound are
ignored, for example:
$c->parse(<<ENDC);
struct header {
int id;
int len;
unsigned flags;
};
struct message {
struct header;
short samples[32];
};
ENDC
for my $type (qw( header message header.len )) {
$c->tag($type, Hooks => { unpack => sub { print "unpack: $type\n"; @_ } });
}
for my $type (qw( header message )) {
print "[unpacking $type]\n";
$u = $c->unpack($type, $data);
}
This will print:
[unpacking header]
unpack: header.len
unpack: header
[unpacking message]
unpack: header.len
unpack: message
As you can see from the above output, tags attached to members of inlined
compounds ("header.len" are still handled.
The following tags can be configured:
"Format" => 'Binary' | 'String'
The "Format" tag allows you to control the way binary data is converted by
"pack" and "unpack".
If you tag a "TYPE" as "Binary", it will not be converted at all, i.e. it will
be passed through as a binary string.
If you tag it as "String", it will be treated like a null-terminated C string,
i.e. "unpack" will convert the C string to a Perl string and vice versa.
See "The Format Tag" for an example.
"ByteOrder" => 'BigEndian' | 'LittleEndian'
The "ByteOrder" tag allows you to explicitly set the byte order of a TYPE.
See "The ByteOrder Tag" for an example.
"Dimension" => '*'
"Dimension" => VALUE
"Dimension" => MEMBER
"Dimension" => SUB
"Dimension" => [ SUB, ARGS ]
The "Dimension" tag allows you to alter the size of an array dynamically.
You can tag fixed size arrays as being flexible using '*'. This is useful if
you cannot use flexible array members in your source code.
$c->tag('type.array', Dimension => '*');
You can also tag an array to have a fixed size different from the one it was
originally declared with.
$c->tag('type.array', Dimension => 42);
If the array is a member of a compound, you can also tag it with to have a
size corresponding to the value of another member in that compound.
$c->tag('type.array', Dimension => 'count');
Finally, you can specify a subroutine that is called when the size of the
array needs to be determined.
$c->tag('type.array', Dimension => \&get_count);
By default, and if the array is a compound member, that subroutine will be
passed a reference to the hash storing the data for the compound.
You can also instruct Convert::Binary::C to pass additional arguments to the
subroutine by passing an array reference instead of the subroutine reference.
This array contains the subroutine reference as well as a list of arguments.
It is possible to define certain special arguments using the "arg" method.
$c->tag('type.array', Dimension => [\&get_count, $c->arg('SELF'), 42]);
See "The Dimension Tag" for various examples.
"Hooks" => { HOOK => SUB, HOOK => [ SUB, ARGS ], ... }, ...
The "Hooks" tag allows you to register subroutines as hooks.
Hooks are called whenever a certain "TYPE" is packed or unpacked. Hooks are
currently considered an experimental feature.
"HOOK" can be one of the following:
pack
unpack
pack_ptr
unpack_ptr
"pack" and "unpack" hooks are called when processing their "TYPE", while
"pack_ptr" and "unpack_ptr" hooks are called when processing pointers to their
"TYPE".
"SUB" is a reference to a subroutine that usually takes one input argument,
processes it and returns one output argument.
Alternatively, you can pass a custom list of arguments to the hook by using an
array reference instead of "SUB" that holds the subroutine reference in the
first element and the arguments to be passed to the subroutine as the other
elements. This way, you can even pass special arguments to the hook using the
"arg" method.
Here are a few examples for registering hooks:
$c->tag('ObjectType', Hooks => {
pack => \&obj_pack,
unpack => \&obj_unpack
});
$c->tag('ProtocolId', Hooks => {
unpack => sub { $protos[$_[0]] }
});
$c->tag('ProtocolId', Hooks => {
unpack_ptr => [sub {
sprintf "$_[0]:{0x%X}", $_[1]
},
$c->arg('TYPE', 'DATA')
],
});
Note that the above example registers both an "unpack" hook and an
"unpack_ptr" hook for "ProtocolId" with two separate calls to "tag". As long
as you don't explicitly overwrite a previously registered hook, it won't be
modified or removed by registering other hooks for the same "TYPE".
To remove all registered hooks for a type, simply remove the "Hooks" tag:
$c->untag('ProtocolId', 'Hooks');
To remove only a single hook, pass "undef" as "SUB" instead of a subroutine
reference:
$c->tag('ObjectType', Hooks => { pack => undef });
If all hooks are removed, the whole "Hooks" tag is removed.
See "The Hooks Tag" for examples on how to use hooks.
untag
"untag" TYPE
"untag" TYPE, TAG1, TAG2, ...
Use the "untag" method to remove one, more, or all tags from a type. If you don't
pass any tag names, all tags attached to the type will be removed. Otherwise only
the listed tags will be removed.
See "USING TAGS" for an example.
arg
"arg" 'ARG', ...
Creates placeholders for special arguments to be passed to hooks or other
subroutines. These arguments are currently:
"SELF"
A reference to the calling Convert::Binary::C object. This may be useful if
you need to work with the object inside the subroutine.
"TYPE"
The name of the type that is currently being processed by the hook.
"DATA"
The data argument that is passed to the subroutine.
"HOOK"
The type of the hook as which the subroutine has been called, for example
"pack" or "unpack_ptr".
"arg" will return a placeholder for each argument it is being passed. Note that
not all arguments may be supported depending on the context of the subroutine.
dependencies
"dependencies"
After some code has been parsed using either the "parse" or "parse_file" methods,
the "dependencies" method can be used to retrieve information about all files that
the object depends on, i.e. all files that have been parsed.
In scalar context, the method returns a hash reference. Each key is the name of a
file. The values are again hash references, each of which holds the size,
modification time (mtime), and change time (ctime) of the file at the moment it
was parsed.
use Convert::Binary::C;
use Data::Dumper;
#----------------------------------------------------------
# Create object, set include path, parse 'string.h' header
#----------------------------------------------------------
my $c = Convert::Binary::C->new
->Include('/usr/lib/gcc/i686-pc-linux-gnu/4.5.2/include',
'/usr/lib/gcc/i686-pc-linux-gnu/4.5.2/include-fixed',
'/usr/include')
->parse_file('string.h');
#----------------------------------------------------------
# Get dependencies of the object, extract dependency files
#----------------------------------------------------------
my $depend = $c->dependencies;
my @files = keys %$depend;
#-----------------------------
# Dump dependencies and files
#-----------------------------
print Data::Dumper->Dump([$depend, \@files],
[qw( depend *files )]);
The above code would print something like this:
$depend = {
'/usr/include/features.h' => {
'ctime' => 1300268052,
'mtime' => 1300267911,
'size' => 12511
},
'/usr/include/gnu/stubs-32.h' => {
'ctime' => 1300268051,
'mtime' => 1300268010,
'size' => 624
},
'/usr/include/sys/cdefs.h' => {
'ctime' => 1300268051,
'mtime' => 1300267957,
'size' => 13195
},
'/usr/include/gnu/stubs.h' => {
'ctime' => 1300268051,
'mtime' => 1300267911,
'size' => 315
},
'/usr/include/string.h' => {
'ctime' => 1300268052,
'mtime' => 1300267944,
'size' => 22572
},
'/usr/lib/gcc/i686-pc-linux-gnu/4.5.2/include/stddef.h' => {
'ctime' => 1300365679,
'mtime' => 1300363914,
'size' => 12542
},
'/usr/include/bits/wordsize.h' => {
'ctime' => 1300268051,
'mtime' => 1300267937,
'size' => 873
},
'/usr/include/xlocale.h' => {
'ctime' => 1300268051,
'mtime' => 1300267915,
'size' => 1764
}
};
@files = (
'/usr/include/features.h',
'/usr/include/gnu/stubs-32.h',
'/usr/include/sys/cdefs.h',
'/usr/include/gnu/stubs.h',
'/usr/include/string.h',
'/usr/lib/gcc/i686-pc-linux-gnu/4.5.2/include/stddef.h',
'/usr/include/bits/wordsize.h',
'/usr/include/xlocale.h'
);
In list context, the method returns the names of all files that have been parsed,
i.e. the following lines are equivalent:
@files = keys %{$c->dependencies};
@files = $c->dependencies;
sourcify
"sourcify"
"sourcify" CONFIG
Returns a string that holds the C source code necessary to represent all parsed C
data structures.
use Convert::Binary::C;
$c = new Convert::Binary::C;
$c->parse(<<'END');
#define ADD(a, b) ((a) + (b))
#define NUMBER 42
typedef struct _mytype mytype;
struct _mytype {
union {
int iCount;
enum count *pCount;
} counter;
#pragma pack( push, 1 )
struct {
char string[NUMBER];
int array[NUMBER/sizeof(int)];
} storage;
#pragma pack( pop )
mytype *next;
};
enum count { ZERO, ONE, TWO, THREE };
END
print $c->sourcify;
The above code would print something like this:
/* typedef predeclarations */
typedef struct _mytype mytype;
/* defined enums */
enum count
{
ZERO,
ONE,
TWO,
THREE
};
/* defined structs and unions */
struct _mytype
{
union
{
int iCount;
enum count *pCount;
} counter;
#pragma pack(push, 1)
struct
{
char string[42];
int array[10];
} storage;
#pragma pack(pop)
mytype *next;
};
The purpose of the "sourcify" method is to enable some kind of platform-
independent caching. The C code generated by "sourcify" can be parsed by any
standard C compiler, as well as of course by the Convert::Binary::C parser.
However, the code may be significantly shorter than the code that has originally
been parsed.
When parsing a typical header file, it's easily possible that you need to open
dozens of other files that are included from that file, and end up parsing several
hundred kilobytes of C code. Since most of it is usually preprocessor directives,
function prototypes and comments, the "sourcify" function strips this down to a
few kilobytes. Saving the "sourcify" string and parsing it next time instead of
the original code may be a lot faster.
The "sourcify" method takes a hash reference as an optional argument. It can be
used to tweak the method's output. The following options can be configured.
"Context" => 0 | 1
Turns preprocessor context information on or off. If this is turned on,
"sourcify" will insert "#line" preprocessor directives in its output. So in
the above example
print $c->sourcify({ Context => 1 });
would print:
/* typedef predeclarations */
typedef struct _mytype mytype;
/* defined enums */
#line 21 "[buffer]"
enum count
{
ZERO,
ONE,
TWO,
THREE
};
/* defined structs and unions */
#line 7 "[buffer]"
struct _mytype
{
#line 8 "[buffer]"
union
{
int iCount;
enum count *pCount;
} counter;
#pragma pack(push, 1)
#line 13 "[buffer]"
struct
{
char string[42];
int array[10];
} storage;
#pragma pack(pop)
mytype *next;
};
Note that "[buffer]" refers to the here-doc buffer when using "parse".
"Defines" => 0 | 1
Turn this on if you want all the defined macros to be part of the source code
output. Given the example code above
print $c->sourcify({ Defines => 1 });
would print:
/* typedef predeclarations */
typedef struct _mytype mytype;
/* defined enums */
enum count
{
ZERO,
ONE,
TWO,
THREE
};
/* defined structs and unions */
struct _mytype
{
union
{
int iCount;
enum count *pCount;
} counter;
#pragma pack(push, 1)
struct
{
char string[42];
int array[10];
} storage;
#pragma pack(pop)
mytype *next;
};
/* preprocessor defines */
#define ADD(a, b) ((a) + (b))
#define NUMBER 42
The macro definitions always appear at the end of the source code. The order
of the macro definitions is undefined.
The following methods can be used to retrieve information about the definitions that have
been parsed. The examples given in the description for "enum", "compound" and "typedef"
all assume this piece of C code has been parsed:
#define ABC_SIZE 2
#define MULTIPLY(x, y) ((x)*(y))
#ifdef ABC_SIZE
# define DEFINED
#else
# define NOT_DEFINED
#endif
typedef unsigned long U32;
typedef void *any;
enum __socket_type
{
SOCK_STREAM = 1,
SOCK_DGRAM = 2,
SOCK_RAW = 3,
SOCK_RDM = 4,
SOCK_SEQPACKET = 5,
SOCK_PACKET = 10
};
struct STRUCT_SV {
void *sv_any;
U32 sv_refcnt;
U32 sv_flags;
};
typedef union {
int abc[ABC_SIZE];
struct xxx {
int a;
int b;
} ab[3][4];
any ptr;
} test;
enum_names
"enum_names"
Returns a list of identifiers of all defined enumeration objects. Enumeration
objects don't necessarily have an identifier, so something like
enum { A, B, C };
will obviously not appear in the list returned by the "enum_names" method. Also,
enumerations that are not defined within the source code - like in
struct foo {
enum weekday *pWeekday;
unsigned long year;
};
where only a pointer to the "weekday" enumeration object is used - will not be
returned, even though they have an identifier. So for the above two enumerations,
"enum_names" will return an empty list:
@names = $c->enum_names;
The only way to retrieve a list of all enumeration identifiers is to use the
"enum" method without additional arguments. You can get a list of all enumeration
objects that have an identifier by using
@enums = map { $_->{identifier} || () } $c->enum;
but these may not have a definition. Thus, the two arrays would look like this:
@names = ();
@enums = ('weekday');
The "def" method returns a true value for all identifiers returned by
"enum_names".
enum
enum
"enum" LIST
Returns a list of references to hashes containing detailed information about all
enumerations that have been parsed.
If a list of enumeration identifiers is passed to the method, the returned list
will only contain hash references for those enumerations. The enumeration
identifiers may optionally be prefixed by "enum".
If an enumeration identifier cannot be found, the returned list will contain an
undefined value at that position.
In scalar context, the number of enumerations will be returned as long as the
number of arguments to the method call is not 1. In the latter case, a hash
reference holding information for the enumeration will be returned.
The list returned by the "enum" method looks similar to this:
@enum = (
{
'enumerators' => {
'SOCK_STREAM' => 1,
'SOCK_RAW' => 3,
'SOCK_SEQPACKET' => 5,
'SOCK_RDM' => 4,
'SOCK_PACKET' => 10,
'SOCK_DGRAM' => 2
},
'identifier' => '__socket_type',
'context' => 'definitions.c(13)',
'size' => 4,
'sign' => 0
}
);
"identifier"
holds the enumeration identifier. This key is not present if the enumeration
has no identifier.
"context"
is the context in which the enumeration is defined. This is the filename
followed by the line number in parentheses.
"enumerators"
is a reference to a hash table that holds all enumerators of the enumeration.
"sign"
is a boolean indicating if the enumeration is signed (i.e. has negative
values).
One useful application may be to create a hash table that holds all enumerators of
all defined enumerations:
%enum = map %{ $_->{enumerators} || {} }, $c->enum;
The %enum hash table would then be:
%enum = (
'SOCK_STREAM' => 1,
'SOCK_RAW' => 3,
'SOCK_SEQPACKET' => 5,
'SOCK_RDM' => 4,
'SOCK_DGRAM' => 2,
'SOCK_PACKET' => 10
);
compound_names
"compound_names"
Returns a list of identifiers of all structs and unions (compound data structures)
that are defined in the parsed source code. Like enumerations, compounds don't
need to have an identifier, nor do they need to be defined.
Again, the only way to retrieve information about all struct and union objects is
to use the "compound" method and don't pass it any arguments. If you should need a
list of all struct and union identifiers, you can use:
@compound = map { $_->{identifier} || () } $c->compound;
The "def" method returns a true value for all identifiers returned by
"compound_names".
If you need the names of only the structs or only the unions, use the
"struct_names" and "union_names" methods respectively.
compound
"compound"
"compound" LIST
Returns a list of references to hashes containing detailed information about all
compounds (structs and unions) that have been parsed.
If a list of struct/union identifiers is passed to the method, the returned list
will only contain hash references for those compounds. The identifiers may
optionally be prefixed by "struct" or "union", which limits the search to the
specified kind of compound.
If an identifier cannot be found, the returned list will contain an undefined
value at that position.
In scalar context, the number of compounds will be returned as long as the number
of arguments to the method call is not 1. In the latter case, a hash reference
holding information for the compound will be returned.
The list returned by the "compound" method looks similar to this:
@compound = (
{
'identifier' => 'STRUCT_SV',
'align' => 1,
'context' => 'definitions.c(23)',
'pack' => 0,
'type' => 'struct',
'declarations' => [
{
'declarators' => [
{
'declarator' => '*sv_any',
'size' => 4,
'offset' => 0
}
],
'type' => 'void'
},
{
'declarators' => [
{
'declarator' => 'sv_refcnt',
'size' => 4,
'offset' => 4
}
],
'type' => 'U32'
},
{
'declarators' => [
{
'declarator' => 'sv_flags',
'size' => 4,
'offset' => 8
}
],
'type' => 'U32'
}
],
'size' => 12
},
{
'identifier' => 'xxx',
'align' => 1,
'context' => 'definitions.c(31)',
'pack' => 0,
'type' => 'struct',
'declarations' => [
{
'declarators' => [
{
'declarator' => 'a',
'size' => 4,
'offset' => 0
}
],
'type' => 'int'
},
{
'declarators' => [
{
'declarator' => 'b',
'size' => 4,
'offset' => 4
}
],
'type' => 'int'
}
],
'size' => 8
},
{
'align' => 1,
'context' => 'definitions.c(29)',
'pack' => 0,
'type' => 'union',
'declarations' => [
{
'declarators' => [
{
'declarator' => 'abc[2]',
'size' => 8,
'offset' => 0
}
],
'type' => 'int'
},
{
'declarators' => [
{
'declarator' => 'ab[3][4]',
'size' => 96,
'offset' => 0
}
],
'type' => 'struct xxx'
},
{
'declarators' => [
{
'declarator' => 'ptr',
'size' => 4,
'offset' => 0
}
],
'type' => 'any'
}
],
'size' => 96
}
);
"identifier"
holds the struct or union identifier. This key is not present if the compound
has no identifier.
"context"
is the context in which the struct or union is defined. This is the filename
followed by the line number in parentheses.
"type"
is either 'struct' or 'union'.
"size"
is the size of the struct or union.
"align"
is the alignment of the struct or union.
"pack"
is the struct member alignment if the compound is packed, or zero otherwise.
"declarations"
is an array of hash references describing each struct declaration:
"type"
is the type of the struct declaration. This may be a string or a reference
to a hash describing the type.
"declarators"
is an array of hashes describing each declarator:
"declarator"
is a string representation of the declarator.
"offset"
is the offset of the struct member represented by the current
declarator relative to the beginning of the struct or union.
"size"
is the size occupied by the struct member represented by the current
declarator.
It may be useful to have separate lists for structs and unions. One way to
retrieve such lists would be to use
push @{$_->{type} eq 'union' ? \@unions : \@structs}, $_
for $c->compound;
However, you should use the "struct" and "union" methods, which is a lot simpler:
@structs = $c->struct;
@unions = $c->union;
struct_names
"struct_names"
Returns a list of all defined struct identifiers. This is equivalent to calling
"compound_names", just that it only returns the names of the struct identifiers
and doesn't return the names of the union identifiers.
struct
"struct"
"struct" LIST
Like the "compound" method, but only allows for structs.
union_names
"union_names"
Returns a list of all defined union identifiers. This is equivalent to calling
"compound_names", just that it only returns the names of the union identifiers and
doesn't return the names of the struct identifiers.
union
"union"
"union" LIST
Like the "compound" method, but only allows for unions.
typedef_names
"typedef_names"
Returns a list of all defined typedef identifiers. Typedefs that do not specify a
type that you could actually work with will not be returned.
The "def" method returns a true value for all identifiers returned by
"typedef_names".
typedef
"typedef"
"typedef" LIST
Returns a list of references to hashes containing detailed information about all
typedefs that have been parsed.
If a list of typedef identifiers is passed to the method, the returned list will
only contain hash references for those typedefs.
If an identifier cannot be found, the returned list will contain an undefined
value at that position.
In scalar context, the number of typedefs will be returned as long as the number
of arguments to the method call is not 1. In the latter case, a hash reference
holding information for the typedef will be returned.
The list returned by the "typedef" method looks similar to this:
@typedef = (
{
'declarator' => 'U32',
'type' => 'unsigned long'
},
{
'declarator' => '*any',
'type' => 'void'
},
{
'declarator' => 'test',
'type' => {
'align' => 1,
'context' => 'definitions.c(29)',
'pack' => 0,
'type' => 'union',
'declarations' => [
{
'declarators' => [
{
'declarator' => 'abc[2]',
'size' => 8,
'offset' => 0
}
],
'type' => 'int'
},
{
'declarators' => [
{
'declarator' => 'ab[3][4]',
'size' => 96,
'offset' => 0
}
],
'type' => 'struct xxx'
},
{
'declarators' => [
{
'declarator' => 'ptr',
'size' => 4,
'offset' => 0
}
],
'type' => 'any'
}
],
'size' => 96
}
}
);
"declarator"
is the type declarator.
"type"
is the type specification. This may be a string or a reference to a hash
describing the type. See "enum" and "compound" for a description on how to
interpret this hash.
macro_names
"macro_names"
Returns a list of all defined macro names.
The list returned by the "macro_names" method looks similar to this:
@macro_names = (
'__STDC_VERSION__',
'__STDC_HOSTED__',
'DEFINED',
'MULTIPLY',
'ABC_SIZE'
);
This works only as long as the preprocessor is not reset. See "Preprocessor
configuration" for details.
macro
"macro"
"macro" LIST
Returns the definitions for all defined macros.
If a list of macro names is passed to the method, the returned list will only
contain the definitions for those macros. For undefined macros, "undef" will be
returned.
The list returned by the "macro" method looks similar to this:
@macro = (
'__STDC_VERSION__ 199901L',
'__STDC_HOSTED__ 1',
'DEFINED',
'MULTIPLY(x, y) ((x)*(y))',
'ABC_SIZE 2'
);
This works only as long as the preprocessor is not reset. See "Preprocessor
configuration" for details.
FUNCTIONS
You can alternatively call the following functions as methods on Convert::Binary::C
objects.
feature
"feature" STRING
Checks if Convert::Binary::C was built with certain features. For example,
print "debugging version"
if Convert::Binary::C::feature('debug');
will check if Convert::Binary::C was built with debugging support enabled. The
"feature" function returns 1 if the feature is enabled, 0 if the feature is
disabled, and "undef" if the feature is unknown. Currently the only features that
can be checked are "ieeefp" and "debug".
You can enable or disable certain features at compile time of the module by using
the
perl Makefile.PL enable-feature disable-feature
syntax.
native
"native"
"native" STRING
Returns the value of a property of the native system that Convert::Binary::C was
built on. For example,
$size = Convert::Binary::C::native('IntSize');
will fetch the size of an "int" on the native system. The following properties
can be queried:
Alignment
ByteOrder
CharSize
CompoundAlignment
DoubleSize
EnumSize
FloatSize
HostedC
IntSize
LongDoubleSize
LongLongSize
LongSize
PointerSize
ShortSize
StdCVersion
UnsignedBitfields
UnsignedChars
You can also call "native" without arguments, in which case it will return a
reference to a hash with all properties, like:
$native = {
'StdCVersion' => undef,
'ByteOrder' => 'LittleEndian',
'LongSize' => 4,
'IntSize' => 4,
'HostedC' => 1,
'ShortSize' => 2,
'UnsignedChars' => 0,
'DoubleSize' => 8,
'CharSize' => 1,
'EnumSize' => 4,
'PointerSize' => 4,
'FloatSize' => 4,
'LongLongSize' => 8,
'Alignment' => 4,
'LongDoubleSize' => 12,
'UnsignedBitfields' => 0,
'CompoundAlignment' => 1
};
The contents of that hash are suitable for passing them to the "configure" method.
DEBUGGING
Like perl itself, Convert::Binary::C can be compiled with debugging support that can then
be selectively enabled at runtime. You can specify whether you like to build
Convert::Binary::C with debugging support or not by explicitly giving an argument to
Makefile.PL. Use
perl Makefile.PL enable-debug
to enable debugging, or
perl Makefile.PL disable-debug
to disable debugging. The default will depend on how your perl binary was built. If it was
built with "-DDEBUGGING", Convert::Binary::C will be built with debugging support, too.
Once you have built Convert::Binary::C with debugging support, you can use the following
syntax to enable debug output. Instead of
use Convert::Binary::C;
you simply say
use Convert::Binary::C debug => 'all';
which will enable all debug output. However, I don't recommend to enable all debug output,
because that can be a fairly large amount.
Debugging options
Instead of saying "all", you can pass a string that consists of one or more of the
following characters:
m enable memory allocation tracing
M enable memory allocation & assertion tracing
h enable hash table debugging
H enable hash table dumps
d enable debug output from the XS module
c enable debug output from the ctlib
t enable debug output about type objects
l enable debug output from the C lexer
p enable debug output from the C parser
P enable debug output from the C preprocessor
r enable debug output from the #pragma parser
y enable debug output from yacc (bison)
So the following might give you a brief overview of what's going on inside
Convert::Binary::C:
use Convert::Binary::C debug => 'dct';
When you want to debug memory allocation using
use Convert::Binary::C debug => 'm';
you can use the Perl script check_alloc.pl that resides in the ctlib/util/tool directory
to extract statistics about memory usage and information about memory leaks from the
resulting debug output.
Redirecting debug output
By default, all debug output is written to "stderr". You can, however, redirect the debug
output to a file with the "debugfile" option:
use Convert::Binary::C debug => 'dcthHm',
debugfile => './debug.out';
If the file cannot be opened, you'll receive a warning and the output will go the "stderr"
way again.
Alternatively, you can use the environment variables "CBC_DEBUG_OPT" and "CBC_DEBUG_FILE"
to turn on debug output.
If Convert::Binary::C is built without debugging support, passing the "debug" or
"debugfile" options will cause a warning to be issued. The corresponding environment
variables will simply be ignored.
ENVIRONMENT
"CBC_ORDER_MEMBERS"
Setting this variable to a non-zero value will globally turn on hash key ordering for
compound members. Have a look at the "OrderMembers" option for details.
Setting the variable to the name of a perl module will additionally use this module
instead of the predefined modules for member ordering to tie the hashes to.
"CBC_DEBUG_OPT"
If Convert::Binary::C is built with debugging support, you can use this variable to
specify the debugging options.
"CBC_DEBUG_FILE"
If Convert::Binary::C is built with debugging support, you can use this variable to
redirect the debug output to a file.
"CBC_DISABLE_PARSER"
This variable is intended purely for development. Setting it to a non-zero value disables
the Convert::Binary::C parser, which means that no information is collected from the file
or code that is parsed. However, the preprocessor will run, which is useful for
benchmarking the preprocessor.
FLEXIBLE ARRAY MEMBERS AND INCOMPLETE TYPES
Flexible array members are a feature introduced with ISO-C99. It's a common problem that
you have a variable length data field at the end of a structure, for example an array of
characters at the end of a message struct. ISO-C99 allows you to write this as:
struct message {
long header;
char data[];
};
The advantage is that you clearly indicate that the size of the appended data is variable,
and that the "data" member doesn't contribute to the size of the "message" structure.
When packing or unpacking data, Convert::Binary::C deals with flexible array members as if
their length was adjustable. For example, "unpack" will adapt the length of the array
depending on the input string:
$msg1 = $c->unpack('message', 'abcdefg');
$msg2 = $c->unpack('message', 'abcdefghijkl');
The following data is unpacked:
$msg1 = {
'data' => [
101,
102,
103
],
'header' => 1633837924
};
$msg2 = {
'data' => [
101,
102,
103,
104,
105,
106,
107,
108
],
'header' => 1633837924
};
Similarly, pack will adjust the length of the output string according to the data you feed
in:
use Data::Hexdumper;
$msg = {
header => 4711,
data => [0x10, 0x20, 0x30, 0x40, 0x77..0x88],
};
$data = $c->pack('message', $msg);
print hexdump(data => $data);
This would print:
0x0000 : 00 00 12 67 10 20 30 40 77 78 79 7A 7B 7C 7D 7E : ...g..0@wxyz{|}~
0x0010 : 7F 80 81 82 83 84 85 86 87 88 : ..........
Incomplete types such as
typedef unsigned long array[];
are handled in exactly the same way. Thus, you can easily
$array = $c->unpack('array', '?'x20);
which will unpack the following array:
$array = [
1061109567,
1061109567,
1061109567,
1061109567,
1061109567
];
You can also alter the length of an array using the "Dimension" tag.
FLOATING POINT VALUES
When using Convert::Binary::C to handle floating point values, you have to be aware of
some limitations.
You're usually safe if all your platforms are using the IEEE floating point format. During
the Convert::Binary::C build process, the "ieeefp" feature will automatically be enabled
if the host is using IEEE floating point. You can check for this feature at runtime using
the "feature" function:
if (Convert::Binary::C::feature('ieeefp')) {
# do something
}
When IEEE floating point support is enabled, the module can also handle floating point
values of a different byteorder.
If your host platform is not using IEEE floating point, the "ieeefp" feature will be
disabled. Convert::Binary::C then will be more restrictive, refusing to handle any non-
native floating point values.
However, Convert::Binary::C cannot detect the floating point format used by your target
platform. It can only try to prevent problems in obvious cases. If you know your target
platform has a completely different floating point format, don't use floating point
conversion at all.
Whenever Convert::Binary::C detects that it cannot properly do floating point value
conversion, it will issue a warning and will not attempt to convert the floating point
value.
BITFIELDS
Bitfield support in Convert::Binary::C is currently in an experimental state. You are
encouraged to test it, but you should not blindly rely on its results.
You are also encouraged to supply layouting algorithms for compilers whose bitfield
implementation is not handled correctly at the moment. Even better that the plain
algorithm is of course a patch that adds a new bitfield layouting engine.
While bitfields may not be handled correctly by the conversion routines yet, they are
always parsed correctly. This means that you can reliably use the declarator fields as
returned by the "struct" or "typedef" methods. Given the following source
struct bitfield {
int seven:7;
int :1;
int four:4, :0;
int integer;
};
a call to "struct" will return
@struct = (
{
'identifier' => 'bitfield',
'align' => 1,
'context' => 'bitfields.c(1)',
'pack' => 0,
'type' => 'struct',
'declarations' => [
{
'declarators' => [
{
'declarator' => 'seven:7'
}
],
'type' => 'int'
},
{
'declarators' => [
{
'declarator' => ':1'
}
],
'type' => 'int'
},
{
'declarators' => [
{
'declarator' => 'four:4'
},
{
'declarator' => ':0'
}
],
'type' => 'int'
},
{
'declarators' => [
{
'declarator' => 'integer',
'size' => 4,
'offset' => 4
}
],
'type' => 'int'
}
],
'size' => 8
}
);
No size/offset keys will currently be returned for bitfield entries.
MULTITHREADING
Convert::Binary::C was designed to be thread-safe.
INHERITANCE
If you wish to derive a new class from Convert::Binary::C, this is relatively easy.
Despite their XS implementation, Convert::Binary::C objects are actually blessed hash
references.
The XS data is stored in a read-only hash value for the key that is the empty string. So
it is safe to use any non-empty hash key when deriving your own class. In addition,
Convert::Binary::C does quite a lot of checks to detect corruption in the object hash.
If you store private data in the hash, you should override the "clone" method and provide
the necessary code to clone your private data. You'll have to call "SUPER::clone", but
this will only clone the Convert::Binary::C part of the object.
For an example of a derived class, you can have a look at Convert::Binary::C::Cached.
PORTABILITY
Convert::Binary::C should build and run on most of the platforms that Perl runs on:
• Various Linux systems
• Various BSD systems
• HP-UX
• Compaq/HP Tru64 Unix
• Mac-OS X
• Cygwin
• Windows 98/NT/2000/XP
Also, many architectures are supported:
• Various Intel Pentium and Itanium systems
• Various Alpha systems
• HP PA-RISC
• Power-PC
• StrongARM
The module should build with any perl binary from 5.004 up to the latest development
version.
COMPARISON WITH SIMILAR MODULES
Most of the time when you're really looking for Convert::Binary::C you'll actually end up
finding one of the following modules. Some of them have different goals, so it's probably
worth pointing out the differences.
C::Include
Like Convert::Binary::C, this module aims at doing conversion from and to binary data
based on C types. However, its configurability is very limited compared to
Convert::Binary::C. Also, it does not parse all C code correctly. It's slower than
Convert::Binary::C, doesn't have a preprocessor. On the plus side, it's written in pure
Perl.
C::DynaLib::Struct
This module doesn't allow you to reuse your C source code. One main goal of
Convert::Binary::C was to avoid code duplication or, even worse, having to maintain
different representations of your data structures. Like C::Include, C::DynaLib::Struct is
rather limited in its configurability.
Win32::API::Struct
This module has a special purpose. It aims at building structs for interfacing Perl code
with Windows API code.
CREDITS
• My love Jennifer for always being there, for filling my life with joy and last but not
least for proofreading the documentation.
• Alain Barbet <alian@cpan.org> for testing and debugging support.
• Mitchell N. Charity for giving me pointers into various interesting directions.
• Alexis Denis for making me improve (externally) and simplify (internally) floating point
support. He can also be blamed (indirectly) for the "initializer" method, as I need it
in my effort to support bitfields some day.
• Michael J. Hohmann <mjh@scientist.de> for endless discussions on our way to and back
home from work, and for making me think about supporting "pack" and "unpack" for
compound members.
• Thorsten Jens <thojens@gmx.de> for testing the package on various platforms.
• Mark Overmeer <mark@overmeer.net> for suggesting the module name and giving invaluable
feedback.
• Thomas Pornin <pornin@bolet.org> for his excellent "ucpp" preprocessor library.
• Marc Rosenthal for his suggestions and support.
• James Roskind, as his C parser was a great starting point to fix all the problems I had
with my original parser based only on the ANSI ruleset.
• Gisbert W. Selke for spotting some interesting bugs and providing extensive reports.
• Steffen Zimmermann for a prolific discussion on the cloning algorithm.
MAILING LIST
There's also a mailing list that you can join:
convert-binary-c@yahoogroups.com
To subscribe, simply send mail to:
convert-binary-c-subscribe@yahoogroups.com
You can use this mailing list for non-bug problems, questions or discussions.
BUGS
I'm sure there are still lots of bugs in the code for this module. If you find any bugs,
Convert::Binary::C doesn't seem to build on your system or any of its tests fail, please
use the CPAN Request Tracker at <http://rt.cpan.org/> to create a ticket for the module.
Alternatively, just send a mail to <mhx@cpan.org>.
EXPERIMENTAL FEATURES
Some features in Convert::Binary::C are marked as experimental. This has most probably
one of the following reasons:
• The feature does not behave in exactly the way that I wish it did, possibly due to some
limitations in the current design of the module.
• The feature hasn't been tested enough and may completely fail to produce the expected
results.
I hope to fix most issues with these experimental features someday, but this may mean that
I have to change the way they currently work in a way that's not backwards compatible. So
if any of these features is useful to you, you can use it, but you should be aware that
the behaviour or the interface may change in future releases of this module.
TODO
If you're interested in what I currently plan to improve (or fix), have a look at the TODO
file.
POSTCARDS
If you're using my module and like it, you can show your appreciation by sending me a
postcard from where you live. I won't urge you to do it, it's completely up to you. To me,
this is just a very nice way of receiving feedback about my work. Please send your
postcard to:
Marcus Holland-Moritz
Kuppinger Weg 28
71116 Gaertringen
GERMANY
If you feel that sending a postcard is too much effort, you maybe want to rate the module
at <http://cpanratings.perl.org/>.
COPYRIGHT
Copyright (c) 2002-2011 Marcus Holland-Moritz. All rights reserved. This program is free
software; you can redistribute it and/or modify it under the same terms as Perl itself.
The "ucpp" library is (c) 1998-2002 Thomas Pornin. For license and redistribution details
refer to ctlib/ucpp/README.
Portions copyright (c) 1989, 1990 James A. Roskind.
The include files located in tests/include/include, which are used in some of the test
scripts are (c) 1991-1999, 2000, 2001 Free Software Foundation, Inc. They are neither
required to create the binary nor linked to the source code of this module in any other
way.
SEE ALSO
See ccconfig, perl, perldata, perlop, perlvar, Data::Dumper and Scalar::Util.