_mbclen, mblen, _mblen_l

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

Important note Important

This API cannot be used in applications that execute in the Windows Runtime. For more information, see CRT functions not supported with /ZW.

size_t _mbclen(
   const unsigned char *c 
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.

_mbclen returns 1 or 2, according to whether the multibyte character c is 1 or 2 bytes long. There is no error return for _mbclen. If mbstr is not NULL, mblen returns the length, in bytes, of the multibyte character. If mbstr is NULL or it points to the wide-character null character, mblen returns 0. If the object that mbstr points to does not form a valid multibyte character within the first count characters, mblen returns –1.

The _mbclen function returns the length, in bytes, of the multibyte character c. If c does not 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 is a valid multibyte character and 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 setting of the LC_CTYPE category setting of the locale; see setlocale for more information. The versions of these functions without the _l suffix use the current locale for this locale-dependent behavior; the versions with the _l suffix are identical except that they use the locale parameter passed in instead. For more information, see Locale.

Generic-Text Routine Mappings

Tchar.h routine

_UNICODE and _MBCS not defined

_MBCS defined

_UNICODE defined


Maps to macro or inline function


Maps to macro or inline function


Required header







For more compatibility information, see Compatibility in the Introduction.

// 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

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.