These routines convert between TUTF-8 and character representations using encodings such as standard UTF-8, UTF-16, ASCII, or Shift-JIS that might be expected by system interfaces or other software components. 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. TUTF-8 provides an intermediate staging ground for all the various encodings. In the example above, text would be translated into TUTF-8 from whatever file encoding the operating system is using. Then it would be translated from TUTF-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.
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_GetEncodingFromObj treats the string representation of objPtr as an encoding name, and finds an encoding with that name, just as Tcl_GetEncoding does. When an encoding is found, it is cached within the objPtr value for future reference, the Tcl_Encoding token is written to the storage pointed to by encodingPtr, and the value TCL_OK is returned. If no such encoding is found, the value TCL_ERROR is returned, and no writing to *encodingPtr takes place. Just as with Tcl_GetEncoding, the caller should call Tcl_FreeEncoding on the resulting encoding token when that token will no longer be used.
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_GetEncodingNulLength returns the length of the terminating nul byte sequence for strings in the specified encoding.
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_GetEncodingNameFromEnvironment retrieves the encoding name to use as the system encoding. On non-Windows platforms, this is derived from the nl_langinfo system call if available, and environment variables LC_ALL, LC_CTYPE or LANG otherwise. On Windows versions Windows 10 Build 18362 and later the returned value is always utf-8. On earlier Windows versions, it is derived from the user settings in the Windows registry. Tcl_GetEncodingNameForUser retrieves the encoding name based on the user settings for the current user and is derived in the same manner as Tcl_GetEncodingNameFromEnvironment on non-Windows platforms. On Windows, unlike Tcl_GetEncodingNameFromEnvironment, it returns the encoding name as per the Windows registry settings irrespective of the Windows version. Both functions accept bufPtr, a pointer to an uninitialized or freed Tcl_DString and write the encoding name to it. They return Tcl_DStringValue(bufPtr) which points to the stored name.
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_SetEncodingSearchPath. This procedure does not ensure that the dynamically-loadable encoding files contain valid data, but merely that they exist.
The flags parameter is a bitmask that controls operation of the conversion and should be a bitwise OR of zero or more of the following values:
The statePtr parameter is an opaque pointer to a location used by the encoding functions to store intermediate state when the data to be converted is passed in multiple chunks. The same location should be passed in statePtr for all related calls with the first chunk passed with the TCL_ENCODING_START flag set and the last with TCL_ENCODING_END set. If statePtr is passed as NULL, all data is presumed to all be contained in that single call and the functions behave as if TCL_ENCODING_START and TCL_ENCODING_END were both set in the flags parameter.
The srcReadPtr, dstWrotePtr and dstCharsPtr point to locations to hold the number of bytes in the source that were processed successfully, the number of bytes written to the output buffer (excluding terminating nulls), and the number of characters written to the output buffer (again excluding terminating nulls) respectively. All three are optional and may be passed as NULL. Further, in the case of the Tcl_ExternalToUtfEx function, the dstCharsPtr may be used with the TCL_ENCODING_CHAR_LIMIT flags to limit the number of characters processed as described earlier.
With the exceptions noted below, the counts returned in srcReadPtr, dstWrotePtr and dstCharsPtr are valid for all return codes listed below other than TCL_ERROR.
The functions Tcl_ExternalToUtf and Tcl_UtfToExternal are variants of Tcl_ExternalToUtfEx and Tcl_UtfToExternalEx. They differ in that their output counts have a limit of INT_MAX and therefore cannot handle the full string lengths supported by Tcl on 64-bit platforms. They will return TCL_ERROR in such cases.
The flags argument to the functions should be 0 or one of the profile selection flags described above to select the profile to use for conversion. The other flags should be cleared. The functions assume the entire source string to be converted is passed into the function.
On success, the function returns TCL_OK with the converted string stored in *dstPtr. For errors other than conversion errors, such as invalid flags, the function returns TCL_ERROR with an error message in interp if it is not NULL. For conversion errors, Tcl_ExternalToUtfDStringEx returns one of the TCL_CONVERT_* errors listed above. When one of these conversion errors is returned, an error message is stored in interp only if errorIdxPtr is NULL. Otherwise, no error message is stored as the function expects the caller is only interested the decoded data up to that point and not treating this as an immediate error condition. The index of the error location is stored in *errorIdxPtr.
Tcl_ExternalToUtfDString and Tcl_UtfToExternalDString are older, less flexible variants of the above functions that do not support profiles. The return value from the functions is a pointer to the value stored in the Tcl_DString. 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_UtfToExternalDString converts a source buffer src from TUTF-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, an encoding-specific default fallback character will be used.
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 TUTF-8. It is defined as follows:
typedef struct {
const char *encodingName;
Tcl_EncodingConvertProc *toUtfProc;
Tcl_EncodingConvertProc *fromUtfProc;
Tcl_EncodingFreeProc *freeProc;
void *clientData;
Tcl_Size 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 TUTF-8. The fromUtfProc refers to a callback procedure to invoke to convert text from TUTF-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(
void *clientData,
const char *src,
int srcLen,
int flags,
Tcl_EncodingState *statePtr,
char *dst,
int dstLen,
int *srcReadIntPtr,
int *dstWroteIntPtr,
int *dstCharsIntPtr);
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. The srcReadIntPtr, dstWroteIntPtr, and dstCharsIntPtr arguments will always be non-NULL, even if the corresponding argument to one of the high-level functions is NULL.
The callback procedure freeProc, if non-NULL, should match the type Tcl_EncodingFreeProc:
typedef void Tcl_EncodingFreeProc(
void *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_GetEncodingSearchPath and Tcl_SetEncodingSearchPath are called to access and set the list of filesystem directories searched for encoding data files.
The value returned by Tcl_GetEncodingSearchPath is the value stored by the last successful call to Tcl_SetEncodingSearchPath. If no calls to Tcl_SetEncodingSearchPath have occurred, Tcl will compute an initial value based on the environment. There is one encoding search path for the entire process, shared by all threads in the process.
Tcl_SetEncodingSearchPath stores searchPath and returns TCL_OK, unless searchPath is not a valid Tcl list, which causes TCL_ERROR to be returned. The elements of searchPath are not verified as existing readable filesystem directories. When searching for encoding data files takes place, and non-existent or non-readable filesystem directories on the searchPath are silently ignored.
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:
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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
The third line of the file is three numbers. The first number is the fallback character (in base 16) to use when converting from TUTF-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 does not 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 that Tcl searches for its script library. If the encoding file exists, but is malformed, an error message will be left in interp.
Tcl_GetEncodingSearchPath returns an object with a reference count of at least 1.
For details about profiles, see the PROFILES section in the documentation of the encoding command.