_mbclen, mblen, _mblen_l, _mbclen_l

Gets the length and determines the validity of a multibyte character.


This API cannot be used in applications that execute in the Windows Runtime. For more information, see CRT functions not supported in Universal Windows Platform apps.


size_t _mbclen(
   const unsigned char *c
size_t _mbclen_l(
   unsigned char const* c,
   _locale_t locale
int mblen(
   const char *mbstr,
   size_t count
int _mblen_l(
   const char *mbstr,
   size_t count,
   _locale_t locale


Multibyte character.

Address of a multibyte-character byte sequence.

Number of bytes to check.

Locale to use.

Return Value

_mbclen and _mbclen_l return 1 or 2, according to the length of the multibyte character c. The functions always return 1 for UTF-8, whether c is multibyte or not. There's no error return for _mbclen.

If mbstr isn't NULL, mblen and _mblen_l return the length, in bytes, of the multibyte character. The mblen and _mblen_l functions work correctly on UTF-8, and may return a value between 1 and 3. When mbstr is NULL (or it points to the wide-character null character), mblen and _mblen_l return 0. The object that mbstr points to must form a valid multibyte character within the first count characters, or mblen and _mblen_l return -1.


The _mbclen function returns the length, in bytes, of the multibyte character c. If c doesn't point to the lead byte of a multibyte character (as determined by an implicit call to _ismbblead, the result of _mbclen is unpredictable.

mblen returns the length in bytes of mbstr if it's a valid multibyte character. It also determines multibyte-character validity associated with the code page. mblen examines count or fewer bytes contained in mbstr, but not more than MB_CUR_MAX bytes.

The output value is affected by the LC_CTYPE category setting of the locale. The versions of these functions without the _l suffix use the current locale for this locale-dependent behavior. The _l suffixed versions behave the same, but they use the locale parameter passed in instead. For more information, see setlocale and Locale.

_mbclen, _mblen_l, and _mbclen_l are Microsoft-specific, not part of the Standard C library. We don't recommend you use them where you want portable code. For Standard C compatibility, use mblen or mbrlen instead.

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

Generic-Text Routine Mappings

Tchar.h routine _UNICODE and _MBCS not defined _MBCS defined _UNICODE defined
_tclen Maps to macro or inline function _mbclen Maps to macro or inline function


Routine Required header
_mbclen <mbstring.h>
mblen <stdlib.h>
_mblen_l <stdlib.h>

For more compatibility information, see Compatibility.


// crt_mblen.c
/* illustrates the behavior of the mblen function

#include <stdlib.h>
#include <stdio.h>

int main( void )
    int      i;
    char    *pmbc = (char *)malloc( sizeof( char ) );
    wchar_t  wc   = L'a';

    printf( "Convert wide character to multibyte character:\n" );
    wctomb_s( &i, pmbc, sizeof(char), wc );
    printf( "   Characters converted: %u\n", i );
    printf( "   Multibyte character: %x\n\n", *pmbc );

    i = mblen( pmbc, MB_CUR_MAX );
    printf( "Length in bytes of multibyte character %x: %u\n", *pmbc, i );

    pmbc = NULL;
    i = mblen( pmbc, MB_CUR_MAX );
    printf( "Length in bytes of NULL multibyte character %x: %u\n", pmbc, i );
Convert wide character to multibyte character:
   Characters converted: 1
   Multibyte character: 61

Length in bytes of multibyte character 61: 1
Length in bytes of NULL multibyte character 0: 0

See also

Character Classification
Interpretation of Multibyte-Character Sequences
_mbccpy, _mbccpy_l
strlen, wcslen, _mbslen, _mbslen_l, _mbstrlen, _mbstrlen_l