Code Conversion(3m17n)

NAME
m17nConv - Code Conversion: Coding system objects and API for them.

  Data Structures
struct MConverter
Structure to be used in code conversion.
struct MCodingInfoISO2022
Structure for a coding system of type MCODING_TYPE_ISO_2022.
struct MCodingInfoUTF
Structure for extra information about a coding system of type MCODING_TYPE_UTF.

  Variables: Symbols representing coding systems
MSymbol Mcoding_us_ascii
Symbol for the coding system US-ASCII.
MSymbol Mcoding_iso_8859_1
Symbol for the coding system ISO-8859-1.
MSymbol Mcoding_utf_8
Symbol for the coding system UTF-8.
MSymbol Mcoding_utf_8_full
Symbol for the coding system UTF-8-FULL.
MSymbol Mcoding_utf_16
Symbol for the coding system UTF-16.
MSymbol Mcoding_utf_16be
Symbol for the coding system UTF-16BE.
MSymbol Mcoding_utf_16le
Symbol for the coding system UTF-16LE.
MSymbol Mcoding_utf_32
Symbol for the coding system UTF-32.
MSymbol Mcoding_utf_32be
Symbol for the coding system UTF-32BE.
MSymbol Mcoding_utf_32le
Symbol for the coding system UTF-32LE.
MSymbol Mcoding_sjis
Symbol for the coding system SJIS.

  Variables: Parameter keys for mconv_define_coding().
MSymbol Mtype
MSymbol Mcharsets
MSymbol Mflags
MSymbol Mdesignation
MSymbol Minvocation
MSymbol Mcode_unit
MSymbol Mbom
MSymbol Mlittle_endian

  Variables: Symbols representing coding system types.
MSymbol Mutf
MSymbol Miso_2022

  Variables: Symbols appearing in the value of #Mflags parameter.
MSymbol Mreset_at_eol
MSymbol Mreset_at_cntl
MSymbol Meight_bit
MSymbol Mlong_form
MSymbol Mdesignation_g0
MSymbol Mdesignation_g1
MSymbol Mdesignation_ctext
MSymbol Mdesignation_ctext_ext
MSymbol Mlocking_shift
MSymbol Msingle_shift
MSymbol Msingle_shift_7
MSymbol Meuc_tw_shift
MSymbol Miso_6429
MSymbol Mrevision_number
MSymbol Mfull_support

  Variables: etc
Remaining variables.
MSymbol Mmaybe
Symbol whose name is 'maybe'.
MSymbol Mcoding
The symbol Mcoding.

  Enumerations
enum MConversionResult { MCONVERSION_RESULT_SUCCESS, MCONVERSION_RESULT_INVALID_BYTE, MCONVERSION_RESULT_INVALID_CHAR, MCONVERSION_RESULT_INSUFFICIENT_SRC, MCONVERSION_RESULT_INSUFFICIENT_DST, MCONVERSION_RESULT_IO_ERROR }
Codes that represent the result of code conversion.
enum MCodingType { MCODING_TYPE_CHARSET, MCODING_TYPE_UTF, MCODING_TYPE_ISO_2022, MCODING_TYPE_MISC }
Types of coding system.
enum MCodingFlagISO2022 { MCODING_ISO_RESET_AT_EOL = 0x1, MCODING_ISO_RESET_AT_CNTL = 0x2, MCODING_ISO_EIGHT_BIT = 0x4, MCODING_ISO_LONG_FORM = 0x8, MCODING_ISO_DESIGNATION_G0 = 0x10, MCODING_ISO_DESIGNATION_G1 = 0x20, MCODING_ISO_DESIGNATION_CTEXT = 0x40, MCODING_ISO_DESIGNATION_CTEXT_EXT = 0x80, MCODING_ISO_LOCKING_SHIFT = 0x100, MCODING_ISO_SINGLE_SHIFT = 0x200, MCODING_ISO_SINGLE_SHIFT_7 = 0x400, MCODING_ISO_EUC_TW_SHIFT = 0x800, MCODING_ISO_ISO6429 = 0x1000, MCODING_ISO_REVISION_NUMBER = 0x2000, MCODING_ISO_FULL_SUPPORT = 0x3000, MCODING_ISO_FLAG_MAX }
Bit-masks to specify the detail of coding system whose type is MCODING_TYPE_ISO_2022.

  Functions
MSymbol mconv_define_coding (const char *name, MPlist *plist, int(*resetter)(MConverter *), int(*decoder)(const unsigned char *, int, MText *, MConverter *), int(*encoder)(MText *, int, int, unsigned char *, int, MConverter *), void *extra_info)
Define a coding system.
MSymbol mconv_resolve_coding (MSymbol symbol)
Resolve coding system name.
int mconv_list_codings (MSymbol **symbols)
List symbols representing coding systems.
MConverter * mconv_buffer_converter (MSymbol name, const unsigned char *buf, int n)
Create a code converter bound to a buffer.
MConverter * mconv_stream_converter (MSymbol name, FILE *fp)
Create a code converter bound to a stream.
int mconv_reset_converter (MConverter *converter)
Reset a code converter.
void mconv_free_converter (MConverter *converter)
Free a code converter.
MConverter * mconv_rebind_buffer (MConverter *converter, const unsigned char *buf, int n)
Bind a buffer to a code converter.
MConverter * mconv_rebind_stream (MConverter *converter, FILE *fp)
Bind a stream to a code converter.
MText * mconv_decode (MConverter *converter, MText *mt)
Decode a byte sequence into an M-text.
MText * mconv_decode_buffer (MSymbol name, const unsigned char *buf, int n)
Decode a buffer area based on a coding system.
MText * mconv_decode_stream (MSymbol name, FILE *fp)
Decode a stream input based on a coding system.
int mconv_encode (MConverter *converter, MText *mt)
Encode an M-text into a byte sequence.
int mconv_encode_range (MConverter *converter, MText *mt, int from, int to)
Encode a part of an M-text.
int mconv_encode_buffer (MSymbol name, MText *mt, unsigned char *buf, int n)
Encode an M-text into a buffer area.
int mconv_encode_stream (MSymbol name, MText *mt, FILE *fp)
Encode an M-text to write to a stream.
int mconv_getc (MConverter *converter)
Read a character via a code converter.
int mconv_ungetc (MConverter *converter, int c)
Push a character back to a code converter.
int mconv_putc (MConverter *converter, int c)
Write a character via a code converter.
MText * mconv_gets (MConverter *converter, MText *mt)
Read a line using a code converter.

Detailed Description

Coding system objects and API for them.

The m17n library represents a character encoding scheme (CES) of coded character sets (CCS) as an object called coding system. Application programs can add original coding systems.

To encode means converting code-points to character codes and to decode means converting character codes back to code-points.

Application programs can decode a byte sequence with a specified coding system into an M-text, and inversely, can encode an M-text into a byte sequence.

Data Structure Documentation

  MConverter

Structure to be used in code conversion.

FIELD DOCUMENTATION:

int MConverter::lenient

Set the value to nonzero if the conversion should be lenient. By default, the conversion is strict (i.e. not lenient).

If the conversion is strict, the converter stops at the first invalid byte (on decoding) or at the first character not supported by the coding system (on encoding). If this happens, MConverter->result is set to MCONVERSION_RESULT_INVALID_BYTE or MCONVERSION_RESULT_INVALID_CHAR accordingly.

If the conversion is lenient, on decoding, an invalid byte is kept per se, and on encoding, an invalid character is replaced with '<U+XXXX>' (if the character is a Unicode character) or with '<M+XXXXXX>' (otherwise).

int MConverter::last_block

Set the value to nonzero before decoding or encoding the last block of the byte sequence or the character sequence respectively. The value influences the conversion as below.

On decoding, in the case that the last few bytes are too short to form a valid byte sequence:

If the value is nonzero, the conversion terminates by error (MCONVERSION_RESULT_INVALID_BYTE) at the first byte of the sequence.

If the value is zero, the conversion terminates successfully. Those bytes are stored in the converter as carryover and are prepended to the byte sequence of the further conversion.

On encoding, in the case that the coding system is context dependent:

If the value is nonzero, the conversion may produce a byte sequence at the end to reset the context to the initial state even if the source characters are zero.

If the value is zero, the conversion never produce such a byte sequence at the end.

unsigned MConverter::at_most

If the value is nonzero, it specifies at most how many characters to convert.

int MConverter::nchars

The following three members are to report the result of the conversion.

Number of characters most recently decoded or encoded.

int MConverter::nbytes

Number of bytes recently decoded or encoded.

enum MConversionResult MConverter::result

Result code of the conversion.

union { ... } MConverter::status

Various information about the status of code conversion. The contents depend on the type of coding system. It is assured that status is aligned so that any type of casting is safe and at least 256 bytes of memory space can be used.

void* MConverter::internal_info

This member is for internally use only. An application program should never touch it.

  MCodingInfoISO2022

Structure for a coding system of type MCODING_TYPE_ISO_2022.

FIELD DOCUMENTATION:

int MCodingInfoISO2022::initial_invocation[2]

Table of numbers of an ISO2022 code extension element invoked to each graphic plane (Graphic Left and Graphic Right). -1 means no code extension element is invoked to that plane.

char MCodingInfoISO2022::designations[32]

Table of code extension elements. The Nth element corresponds to the Nth charset in charset_names, which is an argument given to the mconv_define_coding() function.

If an element value is 0..3, it specifies a graphic register number to designate the corresponds charset. In addition, the charset is initially designated to that graphic register.

If the value is -4..-1, it specifies a graphic register number 0..3 respectively to designate the corresponds charset. Initially, the charset is not designated to any graphic register.

unsigned MCodingInfoISO2022::flags

Bitwise OR of enum MCodingFlagISO2022 .

  MCodingInfoUTF

Structure for extra information about a coding system of type MCODING_TYPE_UTF.

FIELD DOCUMENTATION:

int MCodingInfoUTF::code_unit_bits

Specify bits of a code unit. The value must be 8, 16, or 32.

int MCodingInfoUTF::bom

Specify how to handle the heading BOM (byte order mark). The value must be 0, 1, or 2. The meanings are as follows:

0: On decoding, check the first two byte. If they are BOM, decide endian by them. If not, decide endian by the member endian. On encoding, produce byte sequence according to endian with heading BOM.

1: On decoding, do not handle the first two bytes as BOM, and decide endian by endian. On encoding, produce byte sequence according to endian without BOM.

2: On decoding, handle the first two bytes as BOM and decide ending by them. On encoding, produce byte sequence according to endian with heading BOM.

If <code_unit_bits> is 8, the value has no meaning.

int MCodingInfoUTF::endian

Specify the endian type. The value must be 0 or 1. 0 means little endian, and 1 means big endian.

If <code_unit_bits> is 8, the value has no meaning.

Enumeration Type Documentation

  enum MCodingFlagISO2022

Bit-masks to specify the detail of coding system whose type is MCODING_TYPE_ISO_2022.

Enumerator:

MCODING_ISO_RESET_AT_EOL
    On encoding, reset the invocation and designation status to initial at end of line.

MCODING_ISO_RESET_AT_CNTL
    On encoding, reset the invocation and designation status to initial before any control codes.

MCODING_ISO_EIGHT_BIT
    Use the right graphic plane.

MCODING_ISO_LONG_FORM
    Use the non-standard 4 bytes format for designation sequence for charsets JISX0208-1978, GB2312, and JISX0208-1983.

MCODING_ISO_DESIGNATION_G0
    On encoding, unless explicitly specified, designate charsets to G0.

MCODING_ISO_DESIGNATION_G1
    On encoding, unless explicitly specified, designate charsets except for ASCII to G1.

MCODING_ISO_DESIGNATION_CTEXT
    On encoding, unless explicitly specified, designate 94-chars charsets to G0, 96-chars charsets to G1.

MCODING_ISO_DESIGNATION_CTEXT_EXT
    On encoding, encode such charsets not conforming to ISO-2022 by ESC % / ..., and encode non-supported Unicode characters by ESC % G ... ESC % @ . On decoding, handle those escape sequences.

MCODING_ISO_LOCKING_SHIFT
    Use locking shift.

MCODING_ISO_SINGLE_SHIFT
    Use single shift (SS2 (0x8E or ESC N), SS3 (0x8F or ESC O)).

MCODING_ISO_SINGLE_SHIFT_7
    Use 7-bit single shift 2 (SS2 (0x19)).

MCODING_ISO_EUC_TW_SHIFT
    Use EUC-TW like special shifting.

MCODING_ISO_ISO6429
    Use ISO-6429 escape sequences to indicate direction. Not yet implemented.

MCODING_ISO_REVISION_NUMBER
    On encoding, if a charset has revision number, produce escape sequences to specify the number.

MCODING_ISO_FULL_SUPPORT
    Support all ISO-2022 charsets.

  enum MCodingType

Types of coding system.

Enumerator:

MCODING_TYPE_CHARSET
    A coding system of this type supports charsets directly. The dimension of each charset defines the length of bytes to represent a single character of the charset, and a byte sequence directly represents the code-point of a character. The m17n library provides the default decoding and encoding routines of this type.

MCODING_TYPE_UTF
    A coding system of this type supports byte sequences of a UTF (UTF-8, UTF-16, UTF-32) like structure. The m17n library provides the default decoding and encoding routines of this type.

MCODING_TYPE_ISO_2022
    A coding system of this type supports byte sequences of an ISO-2022 like structure. The details of each structure are specified by MCodingInfoISO2022. The m17n library provides decoding and encoding routines of this type.

MCODING_TYPE_MISC
    A coding system of this type is for byte sequences of miscellaneous structures. The m17n library does not provide decoding and encoding routines of this type. They must be provided by the application program.

  enum MConversionResult

Codes that represent the result of code conversion.

One of these values is set in MConverter->result.

Enumerator:

MCONVERSION_RESULT_SUCCESS
    Code conversion is successful.

MCONVERSION_RESULT_INVALID_BYTE
    On decoding, the source contains an invalid byte.

MCONVERSION_RESULT_INVALID_CHAR
    On encoding, the source contains a character that cannot be encoded by the specified coding system.

MCONVERSION_RESULT_INSUFFICIENT_SRC
    On decoding, the source ends with an incomplete byte sequence.

MCONVERSION_RESULT_INSUFFICIENT_DST
    On encoding, the destination is too short to store the result.

MCONVERSION_RESULT_IO_ERROR
    An I/O error occurred in the conversion.

Variable Documentation

  MSymbol Mcoding

The symbol Mcoding.

Any decoded M-text has a text property whose key is the predefined symbol Mcoding. The name of Mcoding is 'coding'.

  MSymbol Mcoding_iso_8859_1

Symbol for the coding system ISO-8859-1.

The symbol Mcoding_iso_8859_1 has name 'iso-8859-1' and represents a coding system for the CES ISO-8859-1.

  MSymbol Mcoding_sjis

Symbol for the coding system SJIS.

The symbol Mcoding_sjis has name 'sjis' and represents a coding system for the CES Shift-JIS.

  MSymbol Mcoding_us_ascii

Symbol for the coding system US-ASCII.

The symbol Mcoding_us_ascii has name 'us-ascii' and represents a coding system for the CES US-ASCII.

  MSymbol Mcoding_utf_16

Symbol for the coding system UTF-16.

The symbol Mcoding_utf_16 has name 'utf-16' and represents a coding system for the CES UTF-16 (RFC 2279).

  MSymbol Mcoding_utf_16be

Symbol for the coding system UTF-16BE.

The symbol Mcoding_utf_16be has name 'utf-16be' and represents a coding system for the CES UTF-16BE (RFC 2279).

  MSymbol Mcoding_utf_16le

Symbol for the coding system UTF-16LE.

The symbol Mcoding_utf_16le has name 'utf-16le' and represents a coding system for the CES UTF-16LE (RFC 2279).

  MSymbol Mcoding_utf_32

Symbol for the coding system UTF-32.

The symbol Mcoding_utf_32 has name 'utf-32' and represents a coding system for the CES UTF-32 (RFC 2279).

  MSymbol Mcoding_utf_32be

Symbol for the coding system UTF-32BE.

The symbol Mcoding_utf_32be has name 'utf-32be' and represents a coding system for the CES UTF-32BE (RFC 2279).

  MSymbol Mcoding_utf_32le

Symbol for the coding system UTF-32LE.

The symbol Mcoding_utf_32le has name 'utf-32le' and represents a coding system for the CES UTF-32LE (RFC 2279).

  MSymbol Mcoding_utf_8

Symbol for the coding system UTF-8.

The symbol Mcoding_utf_8 has name 'utf-8' and represents a coding system for the CES UTF-8.

  MSymbol Mcoding_utf_8_full

Symbol for the coding system UTF-8-FULL.

The symbol Mcoding_utf_8_full has name 'utf-8-full' and represents a coding system that is a extension of UTF-8. This coding system uses the same encoding algorithm as UTF-8 but is not limited to the Unicode characters. It can encode all characters supported by the m17n library.

  MSymbol Mmaybe

Symbol whose name is 'maybe'.

The variable Mmaybe is a symbol of name 'maybe'. It is used a value of Mbom parameter of the function mconv_define_coding() (which see).

  MSymbol Mreset_at_eol

Symbols that can be a value of the Mflags parameter of a coding system used in an argument to the mconv_define_coding() function (which see).

  MSymbol Mtype

Parameter key for mconv_define_coding() (which see).

  MSymbol Mutf

Symbol that can be a value of the Mtype parameter of a coding system used in an argument to the mconv_define_coding() function (which see).

COPYRIGHT
Copyright (C) 2001 Information-technology Promotion Agency (IPA)
Copyright (C) 2001-2008 National Institute of Advanced Industrial Science and Technology (AIST)
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License <http://www.gnu.org/licenses/fdl.html>.