`mbrlen`

Artikel
12/02/2022

Determine the number of bytes that are required to complete a multibyte character in the current locale, with the capability of restarting in the middle of a multibyte character.

Syntax

size_t mbrlen(
   const char * str,
   size_t count,
   mbstate_t * mbstate
);

Parameters

str
Pointer to the next byte to inspect in a multibyte character string.

count
The maximum number of bytes to inspect.

mbstate
Pointer to the current shift state of the initial byte of str.

Return value

One of the following values:

Value	Description
0	The next `count` or fewer bytes complete the multibyte character that represents the wide null character.
1 to `count`, inclusive	The next `count` or fewer bytes complete a valid multibyte character. The value returned is the number of bytes that complete the multibyte character.
(size_t)(-2)	The next `count` bytes contribute to an incomplete but potentially valid multibyte character and all `count` bytes have been processed.
(size_t)(-1)	An encoding error occurred. The next `count` or fewer bytes don't contribute to a complete and valid multibyte character. In this case, `errno` is set to EILSEQ and the conversion state in `mbstate` is unspecified.

Remarks

The mbrlen function inspects at most count bytes starting with the byte pointed to by str to determine the number of bytes that are required to complete the next multibyte character, including any shift sequences. It's equivalent to the call mbrtowc(NULL, str, count, &mbstate) where mbstate is either a user-provided mbstate_t object, or a static internal object provided by the library.

The mbrlen function saves and uses the shift state of an incomplete multibyte character in the mbstate parameter. It's why **mbrlen**can restart in the middle of a multibyte character, if needed, and examine at most count bytes. If mbstate is a null pointer, mbrlen uses an internal, static mbstate_t object to store the shift state. Because the internal mbstate_t object isn't thread-safe, we recommend that you always allocate and pass your own mbstate parameter.

The mbrlen function differs from _mbclen, mblen, _mblen_l by its restartability. The shift state is stored in mbstate for subsequent calls to the same or other restartable functions. Results are undefined when mixing the use of restartable and nonrestartable functions. For example, an application should use wcsrlen instead of wcslen if a subsequent call to wcsrtombs is used instead of wcstombs.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Generic-text routine mappings

TCHAR.H routine	`_UNICODE` and `_MBCS` not defined	`_MBCS` defined	`_UNICODE` defined
not applicable	not applicable	`mbrlen`	not applicable

Requirements

Routine	Required header
`mbrlen`	<wchar.h>

For more compatibility information, see Compatibility.

Example

This example shows how the interpretation of multibyte characters depends on the current code page, and demonstrates the resuming capability of mbrlen.

// crt_mbrlen.c
// Compile by using: cl crt_mbrlen.c
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <locale.h>
#include <wchar.h>

size_t Example(const char * pStr)
{
    size_t      charLen = 0;
    size_t      charCount = 0;
    mbstate_t   mbState = {0};

    while ((charLen = mbrlen(pStr++, 1, &mbState)) != 0 &&
            charLen != (size_t)-1)
    {
        if (charLen != (size_t)-2) // if complete mbcs char,
        {
            charCount++;
        }
    }
    return (charCount);
}

int main( void )
{
    int         cp;
    size_t      charCount = 0;
    const char  *pSample =
        "\x82\xD0\x82\xE7\x82\xAA\x82\xC8: Shift-jis hiragana.";

    cp = _getmbcp();
    charCount = Example(pSample);
    printf("\nCode page: %d\n%s\nCharacter count: %d\n",
        cp, pSample, charCount);

    setlocale(LC_ALL, "ja-JP"); // Set Japanese locale
    _setmbcp(932); // and Japanese multibyte code page
    cp = _getmbcp();
    charCount = Example(pSample);
    printf("\nCode page: %d\n%s\nCharacter count: %d\n",
        cp, pSample, charCount);
}


Code page: 0
é╨éτé¬é╚: Shift-jis hiragana.
Character count: 29

Code page: 932
????: Shift-jis hiragana.
Character count: 25

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