Null-terminated multibyte strings
A null-terminated multibyte string (NTMBS), or "multibyte string", is a sequence of nonzero bytes followed by a byte with value zero (the terminating null character).
Each character stored in the string may occupy more than one byte. The encoding used to represent characters in a multibyte character string is locale-specific: it may be UTF-8, GB18030, EUC-JP, Shift-JIS, etc. For example, the char array {'\xe4','\xbd','\xa0','\xe5','\xa5','\xbd','\0'} is an NTMBS holding the string "你好" in UTF-8 multibyte encoding: the first three bytes encode the character 你, the next three bytes encode the character 好. The same string encoded in GB18030 is the char array {'\xc4', '\xe3', '\xba', '\xc3', '\0'}, where each of the two characters is encoded as a two-byte sequence.
In some multibyte encodings, any given multibyte character sequence may represent different characters depending on the previous byte sequences, known as "shift sequences". Such encodings are known as state-dependent: knowledge of the current shift state is required to interpret each character. An NTMBS is only valid if it begins and ends in the initial shift state: if a shift sequence was used, the corresponding unshift sequence has to be present before the terminating null character. Examples of such encodings are BOCU-1 and SCSU.
A multibyte character string is layout-compatible with null-terminated byte string (NTBS), that is, can be stored, copied, and examined using the same facilities, except for calculating the number of characters. If the correct locale is in effect, I/O functions also handle multibyte strings. Multibyte strings can be converted to and from wide strings using the following locale-dependent conversion functions:
Multibyte/wide character conversions
| Defined in header
<stdlib.h> | |
| returns the number of bytes in the next multibyte character (function) | |
| converts the next multibyte character to wide character (function) | |
| (哋它亢11) |
converts a wide character to its multibyte representation (function) |
| (哋它亢11) |
converts a narrow multibyte character string to wide string (function) |
| (哋它亢11) |
converts a wide string to narrow multibyte character string (function) |
| Defined in header
<wchar.h> | |
| (哋它亢95) |
checks if the mbstate_t object represents initial shift state (function) |
| (哋它亢95) |
widens a single-byte narrow character to wide character, if possible (function) |
| (哋它亢95) |
narrows a wide character to a single-byte narrow character, if possible (function) |
| (哋它亢95) |
returns the number of bytes in the next multibyte character, given state (function) |
| (哋它亢95) |
converts the next multibyte character to wide character, given state (function) |
| (哋它亢95)(哋它亢11) |
converts a wide character to its multibyte representation, given state (function) |
| (哋它亢95)(哋它亢11) |
converts a narrow multibyte character string to wide string, given state (function) |
| (哋它亢95)(哋它亢11) |
converts a wide string to narrow multibyte character string, given state (function) |
| Defined in header
<uchar.h> | |
| (哋它亢23) |
converts a narrow multibyte character to UTF-8 encoding (function) |
| (哋它亢23) |
converts UTF-8 string to narrow multibyte encoding (function) |
| (哋它亢11) |
generates the next 16-bit wide character from a narrow multibyte string (function) |
| (哋它亢11) |
converts a 16-bit wide character to narrow multibyte string (function) |
| (哋它亢11) |
generates the next 32-bit wide character from a narrow multibyte string (function) |
| (哋它亢11) |
converts a 32-bit wide character to narrow multibyte string (function) |
Types
| Defined in header
<wchar.h> | |
| (哋它亢95) |
conversion state information necessary to iterate multibyte character strings (class) |
| Defined in header
<uchar.h> | |
| (哋它亢23) |
UTF-8 character type, an alias for unsigned char (typedef) |
| (哋它亢11) |
16-bit wide character type (typedef) |
| (哋它亢11) |
32-bit wide character type (typedef) |
Macros
| Defined in header
<limits.h> | |
| MB_LEN_MAX |
maximum number of bytes in a multibyte character, for any supported locale (macro constant) |
| Defined in header
<stdlib.h> | |
| MB_CUR_MAX |
maximum number of bytes in a multibyte character, in the current locale (macro variable) |
References
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 7.10 Sizes of integer types <limits.h> (p: 222)
- 7.22 General utilities <stdlib.h> (p: 340-360)
- 7.28 Unicode utilities <uchar.h> (p: 398-401)
- 7.29 Extended multibyte and wide character utilities <wchar.h> (p: 402-446)
- 7.31.12 General utilities <stdlib.h> (p: 456)
- 7.31.16 Extended multibyte and wide character utilities <wchar.h> (p: 456)
- K.3.6 General utilities <stdlib.h> (p: 604-614)
- K.3.9 Extended multibyte and wide character utilities <wchar.h> (p: 627-651)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 7.10 Sizes of integer types <limits.h> (p: 203)
- 7.20 General utilities <stdlib.h> (p: 306-324)
- 7.24 Extended multibyte and wide character utilities <wchar.h> (p: 348-392)
- 7.26.10 General utilities <stdlib.h> (p: 402)
- 7.26.12 Extended multibyte and wide character utilities <wchar.h> (p: 402)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 4.1.4 Limits <float.h> and <limits.h>
- 4.10 GENERAL UTILITIES <stdlib.h>
- 4.13.7 General utilities <stdlib.h>