Tcl_GetEncoding(3) Tcl Library Procedures Tcl_GetEncoding(3)
____________________________________________________________________________________________________________
NAME
Tcl_GetEncoding, Tcl_FreeEncoding, Tcl_ExternalToUtfDString, Tcl_ExternalToUtf, Tcl_UtfToExternalD-String, Tcl_UtfToExternalDString,
String, Tcl_UtfToExternal, Tcl_WinTCharToUtf, Tcl_WinUtfToTChar, Tcl_GetEncodingName, Tcl_SetSyste-mEncoding, Tcl_SetSystemEncoding,
mEncoding, Tcl_GetEncodingNames, Tcl_CreateEncoding, Tcl_GetDefaultEncodingDir, Tcl_SetDefaultEncod-ingDir Tcl_SetDefaultEncodingDir
ingDir - 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 nega-tive, negative,
tive, 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 con-version conversion
version 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) multiblock)
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 con-version conversion
version routine should return immediately upon reading a
source character that doesn't exist in the target encod-ing; encoding;
ing; otherwise a default fallback character will auto-matically automatically
matically 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 actu-ally actually
ally 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 conver-sion. conversion.
sion. 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 repre-sentations representations
sentations 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 char-acters characters
acters in the source buffer cannot be represented in the target encoding, a default fallback charac-ter character
ter 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 con-verted converted
verted 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 repre-sented represented
sented 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 char-acter character
acter 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_GetEncoding-
Name 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 con-vert convert
vert 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 fol-lows: follows:
lows:
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 proce-dures procedures
dures 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 con-vert convert
vert 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 oneword
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 null-Size nullSize
Size 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 argu-ment argument
ment 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, dst-WrotePtr, dstWrotePtr,
WrotePtr, 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 exam-ple example
ple 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 char-acters, characters,
acters, 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 doublebyte
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 num-ber number
ber 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'' repre-sents represents
sents 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
Tcl 8.1 Tcl_GetEncoding(3)
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