--- name: "Encoding" section: "3tcl" platform: "linux" package: "tcl8.3-doc" version: "8.3.5-13" release: "Debian 5.0 (Lenny)" platforms: ["linux"] url: "https://new.carta.tech/Encoding/3tcl" --- # Encoding(3tcl) procedures for creating and using encodings. ``` ``` ## 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 #include /* Tcl_Win* functions only */ 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) char * Tcl_GetEncodingName(encoding) int Tcl_SetSystemEncoding(interp, name) void Tcl_GetEncodingNames(interp) Tcl_Encoding Tcl_CreateEncoding(typePtr) 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. - 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 psuedo-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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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 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