Provided by: tcl8.4-doc_8.4.20-7_all 
NAME
Tcl_GetEncoding, Tcl_FreeEncoding, Tcl_ExternalToUtfDString, Tcl_ExternalToUtf, Tcl_UtfToExternalDString,
Tcl_UtfToExternal, Tcl_WinTCharToUtf, Tcl_WinUtfToTChar, Tcl_GetEncodingName, Tcl_SetSystemEncoding,
Tcl_GetEncodingNames, Tcl_CreateEncoding, Tcl_GetDefaultEncodingDir, Tcl_SetDefaultEncodingDir -
procedures for creating and using encodings.
SYNOPSIS
#include <tcl.h>
Tcl_Encoding
Tcl_GetEncoding(interp, name)
void
Tcl_FreeEncoding(encoding)
char *
Tcl_ExternalToUtfDString(encoding, src, srcLen, dstPtr)
int
Tcl_ExternalToUtf(interp, encoding, src, srcLen, flags, statePtr, dst, dstLen, srcReadPtr, dstWrotePtr,
dstCharsPtr)
char *
Tcl_UtfToExternalDString(encoding, src, srcLen, dstPtr)
int
Tcl_UtfToExternal(interp, encoding, src, srcLen, flags, statePtr, dst, dstLen, srcReadPtr, dstWrotePtr,
dstCharsPtr)
char *
Tcl_WinTCharToUtf(tsrc, srcLen, dstPtr)
TCHAR *
Tcl_WinUtfToTChar(src, srcLen, dstPtr)
CONST char *
Tcl_GetEncodingName(encoding)
int
Tcl_SetSystemEncoding(interp, name)
void
Tcl_GetEncodingNames(interp)
Tcl_Encoding
Tcl_CreateEncoding(typePtr)
CONST char *
Tcl_GetDefaultEncodingDir(void)
void
Tcl_SetDefaultEncodingDir(path)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter to use for error reporting, or NULL if no error
reporting is desired.
CONST char *name (in) Name of encoding to load.
Tcl_Encoding encoding (in) The encoding to query, free, or use for converting text. If
encoding is NULL, the current system encoding is used.
CONST char *src (in) For the Tcl_ExternalToUtf functions, an array of bytes in
the specified encoding that are to be converted to UTF-8.
For the Tcl_UtfToExternal and Tcl_WinUtfToTChar functions,
an array of UTF-8 characters to be converted to the
specified encoding.
CONST TCHAR *tsrc (in) An array of Windows TCHAR characters to convert to UTF-8.
int srcLen (in) Length of src or tsrc in bytes. If the length is negative,
the encoding-specific length of the string is used.
Tcl_DString *dstPtr (out) Pointer to an uninitialized or free Tcl_DString in which the
converted result will be stored.
int flags (in) Various flag bits OR-ed together. TCL_ENCODING_START
signifies that the source buffer is the first block in a
(potentially multi-block) input stream, telling the
conversion routine to reset to an initial state and perform
any initialization that needs to occur before the first byte
is converted. TCL_ENCODING_END signifies that the source
buffer is the last block in a (potentially multi-block)
input stream, telling the conversion routine to perform any
finalization that needs to occur after the last byte is
converted and then to reset to an initial state.
TCL_ENCODING_STOPONERROR signifies that the conversion
routine should return immediately upon reading a source
character that doesn't exist in the target encoding;
otherwise a default fallback character will automatically be
substituted.
Tcl_EncodingState *statePtr (in/out) Used when converting a (generally long or indefinite length)
byte stream in a piece by piece fashion. The conversion
routine stores its current state in *statePtr after src (the
buffer containing the current piece) has been converted;
that state information must be passed back when converting
the next piece of the stream so the conversion routine knows
what state it was in when it left off at the end of the last
piece. May be NULL, in which case the value specified for
flags is ignored and the source buffer is assumed to contain
the complete string to convert.
char *dst (out) Buffer in which the converted result will be stored. No
more than dstLen bytes will be stored in dst.
int dstLen (in) The maximum length of the output buffer dst in bytes.
int *srcReadPtr (out) Filled with the number of bytes from src that were actually
converted. This may be less than the original source length
if there was a problem converting some source characters.
May be NULL.
int *dstWrotePtr (out) Filled with the number of bytes that were actually stored in
the output buffer as a result of the conversion. May be
NULL.
int *dstCharsPtr (out) Filled with the number of characters that correspond to the
number of bytes stored in the output buffer. May be NULL.
Tcl_EncodingType *typePtr (in) Structure that defines a new type of encoding.
CONST char *path (in) A path to the location of the encoding file.
_________________________________________________________________
INTRODUCTION
These routines convert between Tcl's internal character representation, UTF-8, and character
representations used by various operating systems or file systems, such as Unicode, ASCII, or Shift-JIS.
When operating on strings, such as such as obtaining the names of files or displaying characters using
international fonts, the strings must be translated into one or possibly multiple formats that the
various system calls can use. For instance, on a Japanese Unix workstation, a user might obtain a
filename represented in the EUC-JP file encoding and then translate the characters to the jisx0208 font
encoding in order to display the filename in a Tk widget. The purpose of the encoding package is to help
bridge the translation gap. UTF-8 provides an intermediate staging ground for all the various encodings.
In the example above, text would be translated into UTF-8 from whatever file encoding the operating
system is using. Then it would be translated from UTF-8 into whatever font encoding the display routines
require.
Some basic encodings are compiled into Tcl. Others can be defined by the user or dynamically loaded from
encoding files in a platform-independent manner.
DESCRIPTION
Tcl_GetEncoding finds an encoding given its name. The name may refer to a builtin Tcl encoding, a user-
defined encoding registered by calling Tcl_CreateEncoding, or a dynamically-loadable encoding file. The
return value is a token that represents the encoding and can be used in subsequent calls to procedures
such as Tcl_GetEncodingName, Tcl_FreeEncoding, and Tcl_UtfToExternal. If the name did not refer to any
known or loadable encoding, NULL is returned and an error message is returned in interp.
The encoding package maintains a database of all encodings currently in use. The first time name is
seen, Tcl_GetEncoding returns an encoding with a reference count of 1. If the same name is requested
further times, then the reference count for that encoding is incremented without the overhead of
allocating a new encoding and all its associated data structures.
When an encoding is no longer needed, Tcl_FreeEncoding should be called to release it. When an encoding
is no longer in use anywhere (i.e., it has been freed as many times as it has been gotten)
Tcl_FreeEncoding will release all storage the encoding was using and delete it from the database.
Tcl_ExternalToUtfDString converts a source buffer src from the specified encoding into UTF-8. The
converted bytes are stored in dstPtr, which is then null-terminated. The caller should eventually call
Tcl_DStringFree to free any information stored in dstPtr. When converting, if any of the characters in
the source buffer cannot be represented in the target encoding, a default fallback character will be
used. The return value is a pointer to the value stored in the DString.
Tcl_ExternalToUtf converts a source buffer src from the specified encoding into UTF-8. Up to srcLen
bytes are converted from the source buffer and up to dstLen converted bytes are stored in dst. In all
cases, *srcReadPtr is filled with the number of bytes that were successfully converted from src and
*dstWrotePtr is filled with the corresponding number of bytes that were stored in dst. The return value
is one of the following:
TCL_OK All bytes of src were converted.
TCL_CONVERT_NOSPACE The destination buffer was not large enough for all of the converted
data; as many characters as could fit were converted though.
TCL_CONVERT_MULTIBYTE The last fews bytes in the source buffer were the beginning of a
multibyte sequence, but more bytes were needed to complete this
sequence. A subsequent call to the conversion routine should pass a
buffer containing the unconverted bytes that remained in src plus
some further bytes from the source stream to properly convert the
formerly split-up multibyte sequence.
TCL_CONVERT_SYNTAX The source buffer contained an invalid character sequence. This may
occur if the input stream has been damaged or if the input encoding
method was misidentified.
TCL_CONVERT_UNKNOWN The source buffer contained a character that could not be represented
in the target encoding and TCL_ENCODING_STOPONERROR was specified.
Tcl_UtfToExternalDString converts a source buffer src from UTF-8 into the specified encoding. The
converted bytes are stored in dstPtr, which is then terminated with the appropriate encoding-specific
null. The caller should eventually call Tcl_DStringFree to free any information stored in dstPtr. When
converting, if any of the characters in the source buffer cannot be represented in the target encoding, a
default fallback character will be used. The return value is a pointer to the value stored in the
DString.
Tcl_UtfToExternal converts a source buffer src from UTF-8 into the specified encoding. Up to srcLen
bytes are converted from the source buffer and up to dstLen converted bytes are stored in dst. In all
cases, *srcReadPtr is filled with the number of bytes that were successfully converted from src and
*dstWrotePtr is filled with the corresponding number of bytes that were stored in dst. The return values
are the same as the return values for Tcl_ExternalToUtf.
Tcl_WinUtfToTChar and Tcl_WinTCharToUtf are Windows-only convenience functions for converting between
UTF-8 and Windows strings. On Windows 95 (as with the Macintosh and Unix operating systems), all strings
exchanged between Tcl and the operating system are "char" based. On Windows NT, some strings exchanged
between Tcl and the operating system are "char" oriented while others are in Unicode. By convention, in
Windows a TCHAR is a character in the ANSI code page on Windows 95 and a Unicode character on Windows NT.
If you planned to use the same "char" based interfaces on both Windows 95 and Windows NT, you could use
Tcl_UtfToExternal and Tcl_ExternalToUtf (or their Tcl_DString equivalents) with an encoding of NULL (the
current system encoding). On the other hand, if you planned to use the Unicode interface when running on
Windows NT and the "char" interfaces when running on Windows 95, you would have to perform the following
type of test over and over in your program (as represented in pseudo-code):
if (running NT) {
encoding <- Tcl_GetEncoding("unicode");
nativeBuffer <- Tcl_UtfToExternal(encoding, utfBuffer);
Tcl_FreeEncoding(encoding);
} else {
nativeBuffer <- Tcl_UtfToExternal(NULL, utfBuffer);
Tcl_WinUtfToTChar and Tcl_WinTCharToUtf automatically handle this test and use the proper encoding based
on the current operating system. Tcl_WinUtfToTChar returns a pointer to a TCHAR string, and
Tcl_WinTCharToUtf expects a TCHAR string pointer as the src string. Otherwise, these functions behave
identically to Tcl_UtfToExternalDString and Tcl_ExternalToUtfDString.
Tcl_GetEncodingName is roughly the inverse of Tcl_GetEncoding. Given an encoding, the return value is
the name argument that was used to create the encoding. The string returned by Tcl_GetEncodingName is
only guaranteed to persist until the encoding is deleted. The caller must not modify this string.
Tcl_SetSystemEncoding sets the default encoding that should be used whenever the user passes a NULL value
for the encoding argument to any of the other encoding functions. If name is NULL, the system encoding
is reset to the default system encoding, binary. If the name did not refer to any known or loadable
encoding, TCL_ERROR is returned and an error message is left in interp. Otherwise, this procedure
increments the reference count of the new system encoding, decrements the reference count of the old
system encoding, and returns TCL_OK.
Tcl_GetEncodingNames sets the interp result to a list consisting of the names of all the encodings that
are currently defined or can be dynamically loaded, searching the encoding path specified by
Tcl_SetDefaultEncodingDir. This procedure does not ensure that the dynamically-loadable encoding files
contain valid data, but merely that they exist.
Tcl_CreateEncoding defines a new encoding and registers the C procedures that are called back to convert
between the encoding and UTF-8. Encodings created by Tcl_CreateEncoding are thereafter visible in the
database used by Tcl_GetEncoding. Just as with the Tcl_GetEncoding procedure, the return value is a
token that represents the encoding and can be used in subsequent calls to other encoding functions.
Tcl_CreateEncoding returns an encoding with a reference count of 1. If an encoding with the specified
name already exists, then its entry in the database is replaced with the new encoding; the token for the
old encoding will remain valid and continue to behave as before, but users of the new token will now call
the new encoding procedures.
The typePtr argument to Tcl_CreateEncoding contains information about the name of the encoding and the
procedures that will be called to convert between this encoding and UTF-8. It is defined as follows:
typedef struct Tcl_EncodingType {
CONST char *encodingName;
Tcl_EncodingConvertProc *toUtfProc;
Tcl_EncodingConvertProc *fromUtfProc;
Tcl_EncodingFreeProc *freeProc;
ClientData clientData;
int nullSize;
} Tcl_EncodingType;
The encodingName provides a string name for the encoding, by which it can be referred in other procedures
such as Tcl_GetEncoding. The toUtfProc refers to a callback procedure to invoke to convert text from
this encoding into UTF-8. The fromUtfProc refers to a callback procedure to invoke to convert text from
UTF-8 into this encoding. The freeProc refers to a callback procedure to invoke when this encoding is
deleted. The freeProc field may be NULL. The clientData contains an arbitrary one-word value passed to
toUtfProc, fromUtfProc, and freeProc whenever they are called. Typically, this is a pointer to a data
structure containing encoding-specific information that can be used by the callback procedures. For
instance, two very similar encodings such as ascii and macRoman may use the same callback procedure, but
use different values of clientData to control its behavior. The nullSize specifies the number of zero
bytes that signify end-of-string in this encoding. It must be 1 (for single-byte or multi-byte encodings
like ASCII or Shift-JIS) or 2 (for double-byte encodings like Unicode). Constant-sized encodings with 3
or more bytes per character (such as CNS11643) are not accepted.
The callback procedures toUtfProc and fromUtfProc should match the type Tcl_EncodingConvertProc:
typedef int Tcl_EncodingConvertProc(
ClientData clientData,
CONST char *src,
int srcLen,
int flags,
Tcl_Encoding *statePtr,
char *dst,
int dstLen,
int *srcReadPtr,
int *dstWrotePtr,
int *dstCharsPtr);
The toUtfProc and fromUtfProc procedures are called by the Tcl_ExternalToUtf or Tcl_UtfToExternal family
of functions to perform the actual conversion. The clientData parameter to these procedures is the same
as the clientData field specified to Tcl_CreateEncoding when the encoding was created. The remaining
arguments to the callback procedures are the same as the arguments, documented at the top, to
Tcl_ExternalToUtf or Tcl_UtfToExternal, with the following exceptions. If the srcLen argument to one of
those high-level functions is negative, the value passed to the callback procedure will be the
appropriate encoding-specific string length of src. If any of the srcReadPtr, dstWrotePtr, or
dstCharsPtr arguments to one of the high-level functions is NULL, the corresponding value passed to the
callback procedure will be a non-NULL location.
The callback procedure freeProc, if non-NULL, should match the type Tcl_EncodingFreeProc:
typedef void Tcl_EncodingFreeProc(
ClientData clientData);
This freeProc function is called when the encoding is deleted. The clientData parameter is the same as
the clientData field specified to Tcl_CreateEncoding when the encoding was created.
Tcl_GetDefaultEncodingDir and Tcl_SetDefaultEncodingDir access and set the directory to use when locating
the default encoding files. If this value is not NULL, the TclpInitLibraryPath routine appends the path
to the head of the search path, and uses this path as the first place to look into when trying to locate
the encoding file.
ENCODING FILES
Space would prohibit precompiling into Tcl every possible encoding algorithm, so many encodings are
stored on disk as dynamically-loadable encoding files. This behavior also allows the user to create
additional encoding files that can be loaded using the same mechanism. These encoding files contain
information about the tables and/or escape sequences used to map between an external encoding and
Unicode. The external encoding may consist of single-byte, multi-byte, or double-byte characters.
Each dynamically-loadable encoding is represented as a text file. The initial line of the file,
beginning with a ``#'' symbol, is a comment that provides a human-readable description of the file. The
next line identifies the type of encoding file. It can be one of the following letters:
[1] S
A single-byte encoding, where one character is always one byte long in the encoding. An example
is iso8859-1, used by many European languages.
[2] D
A double-byte encoding, where one character is always two bytes long in the encoding. An example
is big5, used for Chinese text.
[3] M
A multi-byte encoding, where one character may be either one or two bytes long. Certain bytes are
a lead bytes, indicating that another byte must follow and that together the two bytes represent
one character. Other bytes are not lead bytes and represent themselves. An example is shiftjis,
used by many Japanese computers.
[4] E
An escape-sequence encoding, specifying that certain sequences of bytes do not represent
characters, but commands that describe how following bytes should be interpreted.
The rest of the lines in the file depend on the type.
Cases [1], [2], and [3] are collectively referred to as table-based encoding files. The lines in a
table-based encoding file are in the same format as this example taken from the shiftjis encoding (this
is not the complete file):
# Encoding file: shiftjis, multi-byte
M
003F 0 40
00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0000000000000000000000000000000000000000000000000000000000000000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 third line of the file is three numbers. The first number is the fallback character (in base 16) to
use when converting from UTF-8 to this encoding. The second number is a 1 if this file represents the
encoding for a symbol font, or 0 otherwise. The last number (in base 10) is how many pages of data
follow.
Subsequent lines in the example above are pages that describe how to map from the encoding into 2-byte
Unicode. The first line in a page identifies the page number. Following it are 256 double-byte numbers,
arranged as 16 rows of 16 numbers. Given a character in the encoding, the high byte of that character is
used to select which page, and the low byte of that character is used as an index to select one of the
double-byte numbers in that page - the value obtained being the corresponding Unicode character. By
examination of the example above, one can see that the characters 0x7E and 0x8163 in shiftjis map to 203E
and 2026 in Unicode, respectively.
Following the first page will be all the other pages, each in the same format as the first: one number
identifying the page followed by 256 double-byte Unicode characters. If a character in the encoding maps
to the Unicode character 0000, it means that the character doesn't actually exist. If all characters on
a page would map to 0000, that page can be omitted.
Case [4] is the escape-sequence encoding file. The lines in an this type of file are in the same format
as this example taken from the iso2022-jp encoding:
# Encoding file: iso2022-jp, escape-driven
E
init {}
final {}
iso8859-1 \x1b(B
jis0201 \x1b(J
jis0208 \x1b$@
jis0208 \x1b$B
jis0212 \x1b$(D
gb2312 \x1b$A
ksc5601 \x1b$(C
In the file, the first column represents an option and the second column is the associated value. init
is a string to emit or expect before the first character is converted, while final is a string to emit or
expect after the last character. All other options are names of table-based encodings; the associated
value is the escape-sequence that marks that encoding. Tcl syntax is used for the values; in the above
example, for instance, ``{}'' represents the empty string and ``\x1b'' represents character 27.
When Tcl_GetEncoding encounters an encoding name that has not been loaded, it attempts to load an
encoding file called name.enc from the encoding subdirectory of each directory specified in the library
path $tcl_libPath. If the encoding file exists, but is malformed, an error message will be left in
interp.
KEYWORDS
utf, encoding, convert