Tcl_GetEncoding(3) Tcl Library Procedures Tcl_GetEncoding(3)______________________________________________________________________________NAME
Tcl_GetEncoding, Tcl_FreeEncoding, Tcl_ExternalToUtfDString,
Tcl_ExternalToUtf, Tcl_UtfToExternalDString, Tcl_UtfToExternal,
Tcl_WinTCharToUtf, Tcl_WinUtfToTChar, Tcl_GetEncodingName, Tcl_SetSys‐
temEncoding, Tcl_GetEncodingNames, Tcl_CreateEncoding, Tcl_GetDefault‐
EncodingDir, 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 convert‐
ing 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 func‐
tions, 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 uninitial‐
ized or free Tcl_DString
in which the converted
result will be stored.
int flags (in) Various flag bits OR-ed
together. TCL_ENCOD‐
ING_START signifies that
the source buffer is the
first block in a (poten‐
tially multi-block) input
stream, telling the con‐
version routine to reset
to an initial state and
perform any initialization
that needs to occur before
the first byte is con‐
verted. 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 conver‐
sion routine should return
immediately upon reading a
source character that
doesn't exist in the tar‐
get encoding; otherwise a
default fallback character
will automatically be sub‐
stituted.
Tcl_EncodingState *statePtr (in/out) Used when converting a
(generally long or indefi‐
nite length) byte stream
in a piece by piece fash‐
ion. The conversion rou‐
tine 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 con‐
verted 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 orig‐
inal source length if
there was a problem con‐
verting some source char‐
acters. May be NULL.
int *dstWrotePtr (out) Filled with the number of
bytes that were actually
stored in the output buf‐
fer 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 buf‐
fer. 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 stag‐
ing ground for all the various encodings. In the example above, text
would be translated into UTF-8 from whatever file encoding the operat‐
ing system is using. Then it would be translated from UTF-8 into what‐
ever 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-inde‐
pendent 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 call‐
ing 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_FreeEn‐
coding, 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 with‐
out 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 speci‐
fied 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 con‐
verting, if any of the characters in the source buffer cannot be repre‐
sented 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 suc‐
cessfully converted from src and *dstWrotePtr is filled with the corre‐
sponding 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 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 for‐
merly 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 encod‐
ing method was misidentified.
TCL_CONVERT_UNKNOWN The source buffer contained a char‐
acter that could not be represented
in the target encoding and
TCL_ENCODING_STOPONERROR was speci‐
fied.
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 informa‐
tion 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 suc‐
cessfully converted from src and *dstWrotePtr is filled with the corre‐
sponding 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 repre‐
sented 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_UtfToExternalD‐
String 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 refer‐
ence 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 dynami‐
cally loaded, searching the encoding path specified by Tcl_SetDefault‐
EncodingDir. This procedure does not ensure that the dynamically-load‐
able encoding files contain valid data, but merely that they exist.
Tcl_CreateEncoding defines a new encoding and registers the C proce‐
dures 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_Cre‐
ateEncoding 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 con‐
vert 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 proce‐
dure 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 dif‐
ferent 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 pro‐
cedures 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 nega‐
tive, the value passed to the callback procedure will be the appropri‐
ate encoding-specific string length of src. If any of the srcReadPtr,
dstWrotePtr, or dstCharsPtr arguments to one of the high-level func‐
tions 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 addi‐
tional 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 repre‐
sent one character. Other bytes are not lead bytes and repre‐
sent 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 corre‐
sponding 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 actu‐
ally 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 col‐
umn 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 exam‐
ple, for instance, ``{}'' represents the empty string and ``\x1b'' rep‐
resents 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)
