Provided by: tcl8.4-doc_8.4.20-7_all bug

NAME

       binary - Insert and extract fields from binary strings

SYNOPSIS

       binary format formatString ?arg arg ...?
       binary scan string formatString ?varName varName ...?
_________________________________________________________________

DESCRIPTION

       This  command  provides  facilities  for manipulating binary data.  The first form, binary
       format, creates a binary string from normal Tcl values.  For example, given the values  16
       and  22,  on a 32 bit architecture, it might produce an 8-byte binary string consisting of
       two 4-byte integers, one for each of the numbers.  The second form of the command,  binary
       scan,  does the opposite: it extracts data from a binary string and returns it as ordinary
       Tcl string values.

BINARY FORMAT

       The binary format command generates a binary string  whose  layout  is  specified  by  the
       formatString  and whose contents come from the additional arguments.  The resulting binary
       value is returned.

       The formatString consists of a sequence of zero or more field specifiers separated by zero
       or  more  spaces.  Each field specifier is a single type character followed by an optional
       numeric count.  Most field specifiers consume one argument  to  obtain  the  value  to  be
       formatted.   The  type  character  specifies  how the value is to be formatted.  The count
       typically indicates how many items of the specified type are taken  from  the  value.   If
       present,  the  count is a non-negative decimal integer or *, which normally indicates that
       all of the items in the value are to be used.  If the number of arguments does  not  match
       the  number  of  fields  in  the  format  string  that consume arguments, then an error is
       generated.

       Here is a small example to clarify the relation  between  the  field  specifiers  and  the
       arguments:
              binary format d3d {1.0 2.0 3.0 4.0} 0.1

       The  first  argument  is  a  list  of  four numbers, but because of the count of 3 for the
       associated field specifier, only the first three will be  used.  The  second  argument  is
       associated  with the second field specifier. The resulting binary string contains the four
       numbers 1.0, 2.0, 3.0 and 0.1.

       Each type-count pair moves an imaginary cursor through the binary data, storing  bytes  at
       the  current  position  and  advancing the cursor to just after the last byte stored.  The
       cursor is initially at position 0 at the beginning of the data.  The type may be  any  one
       of the following characters:

       a    Stores  a  character string of length count in the output string.  Every character is
            taken as modulo 256 (i.e. the low byte of every character is used, and the high  byte
            discarded)  so  when  storing  character  strings  not  wholly  expressible using the
            characters \u0000-\u00ff, the encoding convertto command should be used first if this
            truncation  is  not  desired  (i.e.  if the characters are not part of the ISO 8859-1
            character set.)  If arg has fewer than count bytes, then additional  zero  bytes  are
            used  to  pad  out  the field.  If arg is longer than the specified length, the extra
            characters will be ignored.  If count is *, then all of the  bytes  in  arg  will  be
            formatted.  If count is omitted, then one character will be formatted.  For example,
                   binary format a7a*a alpha bravo charlie
            will return a string equivalent to alpha\000\000bravoc.

       A    This  form is the same as a except that spaces are used for padding instead of nulls.
            For example,
                   binary format A6A*A alpha bravo charlie
            will return alpha bravoc.

       b    Stores a string of count binary digits in low-to-high order within each byte  in  the
            output  string.   Arg  must  contain a sequence of 1 and 0 characters.  The resulting
            bytes are emitted in first to last order with the bits being formatted in low-to-high
            order  within each byte.  If arg has fewer than count digits, then zeros will be used
            for the remaining bits.  If arg has more than the specified  number  of  digits,  the
            extra  digits  will be ignored.  If count is *, then all of the digits in arg will be
            formatted.  If count is omitted, then one digit will be formatted.  If the number  of
            bits  formatted  does not end at a byte boundary, the remaining bits of the last byte
            will be zeros.  For example,
                   binary format b5b* 11100 111000011010
            will return a string equivalent to \x07\x87\x05.

       B    This form is the same as b except that the  bits  are  stored  in  high-to-low  order
            within each byte.  For example,
                   binary format B5B* 11100 111000011010
            will return a string equivalent to \xe0\xe1\xa0.

       h    Stores  a  string  of count hexadecimal digits in low-to-high within each byte in the
            output  string.   Arg  must  contain  a   sequence   of   characters   in   the   set
            ``0123456789abcdefABCDEF''.   The  resulting bytes are emitted in first to last order
            with the hex digits being formatted in low-to-high order within each  byte.   If  arg
            has  fewer  than  count digits, then zeros will be used for the remaining digits.  If
            arg has more than the specified number of digits, the extra digits will  be  ignored.
            If count is *, then all of the digits in arg will be formatted.  If count is omitted,
            then one digit will be formatted.  If the number of digits formatted does not end  at
            a byte boundary, the remaining bits of the last byte will be zeros.  For example,
                   binary format h3h* AB def
            will return a string equivalent to \xba\x00\xed\x0f.

       H    This  form  is  the  same as h except that the digits are stored in high-to-low order
            within each byte.  For example,
                   binary format H3H* ab DEF
            will return a string equivalent to \xab\x00\xde\xf0.

       c    Stores one or more 8-bit integer values  in  the  output  string.   If  no  count  is
            specified, then arg must consist of an integer value; otherwise arg must consist of a
            list containing at least count integer  elements.   The  low-order  8  bits  of  each
            integer  are  stored as a one-byte value at the cursor position.  If count is *, then
            all of the integers in the list are formatted.  If the number of elements in the list
            is  fewer  than  count, then an error is generated.  If the number of elements in the
            list is greater than count, then the extra elements are ignored.  For example,
                   binary format c3cc* {3 -3 128 1} 260 {2 5}
            will return a string equivalent to \x03\xfd\x80\x04\x02\x05, whereas
                   binary format c {2 5}
            will generate an error.

       s    This form is the same as c except that it stores  one  or  more  16-bit  integers  in
            little-endian byte order in the output string.  The low-order 16-bits of each integer
            are stored as a two-byte value at the cursor position with the least significant byte
            stored first.  For example,
                   binary format s3 {3 -3 258 1}
            will return a string equivalent to \x03\x00\xfd\xff\x02\x01.

       S    This  form is the same as s except that it stores one or more 16-bit integers in big-
            endian byte order in the output string.  For example,
                   binary format S3 {3 -3 258 1}
            will return a string equivalent to \x00\x03\xff\xfd\x01\x02.

       i    This form is the same as c except that it stores  one  or  more  32-bit  integers  in
            little-endian byte order in the output string.  The low-order 32-bits of each integer
            are stored as a four-byte value at the cursor position  with  the  least  significant
            byte stored first.  For example,
                   binary format i3 {3 -3 65536 1}
            will return a string equivalent to \x03\x00\x00\x00\xfd\xff\xff\xff\x00\x00\x01\x00

       I    This  form  is  the  same  as  i except that it stores one or more one or more 32-bit
            integers in big-endian byte order in the output string.  For example,
                   binary format I3 {3 -3 65536 1}
            will return a string equivalent to \x00\x00\x00\x03\xff\xff\xff\xfd\x00\x01\x00\x00

       w    This form is the same as c except that it stores  one  or  more  64-bit  integers  in │
            little-endian byte order in the output string.  The low-order 64-bits of each integer │
            are stored as an eight-byte value at the cursor position with the  least  significant │
            byte stored first.  For example,                                                      │
                   binary format w 7810179016327718216                                            │
            will return the string HelloTclW                                                                                          │
            This  form  is  the  same  as  w except that it stores one or more one or more 64-bit │
            integers in big-endian byte order in the output string.  For example,                 │
                   binary format Wc 4785469626960341345 110                                       │
            will return the string BigEndian

       f    This form is the same as c except that it stores one or  more  one  or  more  single-
            precision floating in the machine's native representation in the output string.  This
            representation is not portable across architectures, so it  should  not  be  used  to
            communicate  floating point numbers across the network.  The size of a floating point
            number may vary across architectures, so the number of bytes that are  generated  may
            vary.   If the value overflows the machine's native representation, then the value of
            FLT_MAX as defined by the system will be used  instead.   Because  Tcl  uses  double-
            precision  floating-point  numbers internally, there may be some loss of precision in
            the conversion to single-precision.  For example, on a Windows system running  on  an
            Intel Pentium processor,
                   binary format f2 {1.6 3.4}
            will return a string equivalent to \xcd\xcc\xcc\x3f\x9a\x99\x59\x40.

       d    This  form  is  the  same  as f except that it stores one or more one or more double-
            precision floating in the machine's native representation in the output string.   For
            example, on a Windows system running on an Intel Pentium processor,
                   binary format d1 {1.6}
            will return a string equivalent to \x9a\x99\x99\x99\x99\x99\xf9\x3f.

       x    Stores  count null bytes in the output string.  If count is not specified, stores one
            null byte.  If count is *, generates  an  error.   This  type  does  not  consume  an
            argument.  For example,
                   binary format a3xa3x2a3 abc def ghi
            will return a string equivalent to abc\000def\000\000ghi.

       X    Moves  the  cursor back count bytes in the output string.  If count is * or is larger
            than the current cursor position, then the cursor is positioned at location 0 so that
            the  next  byte  stored  will  be  the  first byte in the result string.  If count is
            omitted then the cursor is moved back one  byte.   This  type  does  not  consume  an
            argument.  For example,
                   binary format a3X*a3X2a3 abc def ghi
            will return dghi.

       @    Moves  the  cursor  to the absolute location in the output string specified by count.
            Position 0 refers to the first byte in the output  string.   If  count  refers  to  a
            position  beyond  the  last byte stored so far, then null bytes will be placed in the
            uninitialized locations and the cursor will be placed at the specified location.   If
            count  is  *,  then  the cursor is moved to the current end of the output string.  If
            count is omitted, then an error will be generated.  This type  does  not  consume  an
            argument. For example,
                   binary format a5@2a1@*a3@10a1 abcde f ghi j
            will return abfdeghi\000\000j.

BINARY SCAN

       The  binary  scan  command  parses  fields  from  a binary string, returning the number of
       conversions performed.  String gives the input to be parsed and formatString indicates how
       to  parse  it.   Each  varName  gives the name of a variable; when a field is scanned from
       string the result is assigned to the corresponding variable.

       As with binary format, the formatString consists of a  sequence  of  zero  or  more  field
       specifiers  separated  by  zero  or  more  spaces.   Each field specifier is a single type
       character followed by an optional  numeric  count.   Most  field  specifiers  consume  one
       argument  to obtain the variable into which the scanned values should be placed.  The type
       character specifies how the binary  data  is  to  be  interpreted.   The  count  typically
       indicates  how  many items of the specified type are taken from the data.  If present, the
       count is a non-negative decimal integer or *, which normally indicates  that  all  of  the
       remaining  items in the data are to be used.  If there are not enough bytes left after the
       current cursor position to satisfy the current field  specifier,  then  the  corresponding
       variable  is  left  untouched  and  binary  scan  returns  immediately  with the number of
       variables that were set.  If there are not enough arguments for all of the fields  in  the
       format string that consume arguments, then an error is generated.

       A  similar  example  as  with  binary  format  should  explain  the relation between field
       specifiers and arguments in case of the binary scan subcommand:
              binary scan $bytes s3s first second

       This command (provided the binary string in the variable bytes is long enough)  assigns  a
       list  of  three  integers to the variable first and assigns a single value to the variable
       second.  If bytes contains fewer than 8 bytes (i.e. four 2-byte integers),  no  assignment
       to  second  will  be  made,  and  if  bytes contains fewer than 6 bytes (i.e. three 2-byte
       integers), no assignment to first will be made.  Hence:
              puts [binary scan abcdefg s3s first second]
              puts $first
              puts $second
       will print (assuming neither variable is set previously):
              1
              25185 25699 26213
              can't read "second": no such variable

       It is important to note that the c, s, and S (and i  and  I  on  64bit  systems)  will  be
       scanned  into  long  data size values.  In doing this, values that have their high bit set
       (0x80 for chars, 0x8000 for shorts, 0x80000000 for ints), will be sign extended.  Thus the
       following will occur:
              set signShort [binary format s1 0x8000]
              binary scan $signShort s1 val; # val == 0xFFFF8000
       If  you  want  to  produce  an  unsigned  value, then you can mask the return value to the
       desired size.  For example, to produce an unsigned short value:
              set val [expr {$val & 0xFFFF}]; # val == 0x8000

       Each type-count pair moves an imaginary cursor through the binary data, reading bytes from
       the current position.  The cursor is initially at position 0 at the beginning of the data.
       The type may be any one of the following characters:

       a    The data is a character string of length count.  If count  is  *,  then  all  of  the
            remaining  bytes  in  string will be scanned into the variable.  If count is omitted,
            then one character will be scanned.  All characters scanned will  be  interpreted  as
            being  in the range \u0000-\u00ff so the encoding convertfrom command might be needed
            if the string is not an ISO 8859-1 string.  For example,
                   binary scan abcde\000fghi a6a10 var1 var2
            will return 1 with the string equivalent to abcde\000 stored in var1  and  var2  left
            unmodified.

       A    This  form  is  the same as a, except trailing blanks and nulls are stripped from the
            scanned value before it is stored in the variable.  For example,
                   binary scan "abc efghi  \000" A* var1
            will return 1 with abc efghi stored in var1.

       b    The data is turned into  a  string  of  count  binary  digits  in  low-to-high  order
            represented  as a sequence of ``1'' and ``0'' characters.  The data bytes are scanned
            in first to last order with the bits being taken in  low-to-high  order  within  each
            byte.   Any  extra bits in the last byte are ignored.  If count is *, then all of the
            remaining bits in string will be scanned.  If count is omitted, then one bit will  be
            scanned.  For example,
                   binary scan \x07\x87\x05 b5b* var1 var2
            will return 2 with 11100 stored in var1 and 1110000110100000 stored in var2.

       B    This  form  is  the  same as b, except the bits are taken in high-to-low order within
            each byte.  For example,
                   binary scan \x70\x87\x05 B5B* var1 var2
            will return 2 with 01110 stored in var1 and 1000011100000101 stored in var2.

       h    The data is turned into a string of count hexadecimal  digits  in  low-to-high  order
            represented  as  a  sequence of characters in the set ``0123456789abcdef''.  The data
            bytes are scanned in first to last order with the hex digits being taken  in  low-to-
            high  order within each byte.  Any extra bits in the last byte are ignored.  If count
            is *, then all of the remaining hex digits in string will be scanned.   If  count  is
            omitted, then one hex digit will be scanned.  For example,
                   binary scan \x07\x86\x05 h3h* var1 var2
            will return 2 with 706 stored in var1 and 50 stored in var2.

       H    This  form  is the same as h, except the digits are taken in high-to-low order within
            each byte.  For example,
                   binary scan \x07\x86\x05 H3H* var1 var2
            will return 2 with 078 stored in var1 and 05 stored in var2.

       c    The data is turned into count 8-bit signed integers and stored in  the  corresponding
            variable  as a list. If count is *, then all of the remaining bytes in string will be
            scanned.  If count is omitted, then one 8-bit integer will be scanned.  For example,
                   binary scan \x07\x86\x05 c2c* var1 var2
            will return 2 with 7 -122 stored in var1  and  5  stored  in  var2.   Note  that  the
            integers  returned are signed, but they can be converted to unsigned 8-bit quantities
            using an expression like:
                   expr { $num & 0xff }

       s    The data is interpreted as count 16-bit signed integers represented in  little-endian
            byte  order.   The  integers  are stored in the corresponding variable as a list.  If
            count is *, then all of the remaining bytes in string will be scanned.  If  count  is
            omitted, then one 16-bit integer will be scanned.  For example,
                   binary scan \x05\x00\x07\x00\xf0\xff s2s* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.  Note that the integers
            returned are signed, but they can be converted to unsigned 16-bit quantities using an
            expression like:
                   expr { $num & 0xffff }

       S    This form is the same as s except that the data is interpreted as count 16-bit signed
            integers represented in big-endian byte order.  For example,
                   binary scan \x00\x05\x00\x07\xff\xf0 S2S* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.

       i    The data is interpreted as count 32-bit signed integers represented in  little-endian
            byte  order.   The  integers  are stored in the corresponding variable as a list.  If
            count is *, then all of the remaining bytes in string will be scanned.  If  count  is
            omitted, then one 32-bit integer will be scanned.  For example,
                   binary scan \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff i2i* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.  Note that the integers
            returned are signed, but they can be converted to unsigned 32-bit quantities using an
            expression like:
                   expr { $num & 0xffffffff }

       I    This form is the same as I except that the data is interpreted as count 32-bit signed
            integers represented in big-endian byte order.  For example,
                   binary scan \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0 I2I* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.

       w    The data is interpreted as count 64-bit signed integers represented in  little-endian │
            byte  order.   The  integers  are stored in the corresponding variable as a list.  If │
            count is *, then all of the remaining bytes in string will be scanned.  If  count  is │
            omitted, then one 64-bit integer will be scanned.  For example,                       │
                   binary scan \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff wi* var1 var2     │
            will  return 2 with 30064771077 stored in var1 and -16 stored in var2.  Note that the │
            integers returned are signed and cannot be represented by Tcl as unsigned values.     │

       W                                                                                          │
            This form is the same as w except that the data is interpreted as count 64-bit signed │
            integers represented in big-endian byte order.  For example,                          │
                   binary scan \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0 WI* var1 var2     │
            will return 2 with 21474836487 stored in var1 and -16 stored in var2.

       f    The  data  is  interpreted  as  count  single-precision floating point numbers in the
            machine's native representation.  The  floating  point  numbers  are  stored  in  the
            corresponding  variable as a list.  If count is *, then all of the remaining bytes in
            string will be scanned.  If count is  omitted,  then  one  single-precision  floating
            point  number  will  be scanned.  The size of a floating point number may vary across
            architectures, so the number of bytes that are scanned may vary.  If  the  data  does
            not  represent  a  valid  floating point number, the resulting value is undefined and
            compiler dependent.  For example, on a Windows system running  on  an  Intel  Pentium
            processor,
                   binary scan \x3f\xcc\xcc\xcd f var1
            will return 1 with 1.6000000238418579 stored in var1.

       d    This  form  is  the  same  as  f except that the data is interpreted as count double-
            precision floating point numbers in the machine's native representation. For example,
            on a Windows system running on an Intel Pentium processor,
                   binary scan \x9a\x99\x99\x99\x99\x99\xf9\x3f d var1
            will return 1 with 1.6000000000000001 stored in var1.

       x    Moves  the cursor forward count bytes in string.  If count is * or is larger than the
            number of bytes after  the  current  cursor  cursor  position,  then  the  cursor  is
            positioned  after  the  last byte in string.  If count is omitted, then the cursor is
            moved forward one byte.  Note that this type  does  not  consume  an  argument.   For
            example,
                   binary scan \x01\x02\x03\x04 x2H* var1
            will return 1 with 0304 stored in var1.

       X    Moves  the  cursor  back  count bytes in string.  If count is * or is larger than the
            current cursor position, then the cursor is positioned at location 0 so that the next
            byte  scanned  will be the first byte in string.  If count is omitted then the cursor
            is moved back one byte.  Note that this type  does  not  consume  an  argument.   For
            example,
                   binary scan \x01\x02\x03\x04 c2XH* var1 var2
            will return 2 with 1 2 stored in var1 and 020304 stored in var2.

       @    Moves  the  cursor  to  the  absolute location in the data string specified by count.
            Note that position 0 refers to the first byte  in  string.   If  count  refers  to  a
            position beyond the end of string, then the cursor is positioned after the last byte.
            If count is omitted, then an error will be generated.  For example,
                   binary scan \x01\x02\x03\x04 c2@1H* var1 var2
            will return 2 with 1 2 stored in var1 and 020304 stored in var2.

PLATFORM ISSUES

       Sometimes it is desirable to format or scan integer values in the native  byte  order  for
       the  machine.   Refer  to  the byteOrder element of the tcl_platform array to decide which
       type character to use when formatting or scanning integers.

EXAMPLES

       This is a procedure to write a Tcl string  to  a  binary-encoded  channel  as  UTF-8  data
       preceded by a length word:
              proc writeString {channel string} {
                  set data [encoding convertto utf-8 $string]
                  puts -nonewline [binary format Ia* \
                          [string length $data] $data]
              }

       This  procedure reads a string from a channel that was written by the previously presented
       writeString procedure:
              proc readString {channel} {
                  if {![binary scan [read $channel 4] I length]} {
                      error "missing length"
                  }
                  set data [read $channel $length]
                  return [encoding convertfrom utf-8 $data]
              }

SEE ALSO

       format(3tcl), scan(3tcl), tclvars(3tcl)

KEYWORDS

       binary, format, scan