wctomb_s, _wctomb_s_l

Converts a wide character to the corresponding multibyte character. A version of wctomb, _wctomb_l with security enhancements as described in Security Enhancements in the CRT.

errno_t wctomb_s(
   int *pRetValue,
   char *mbchar,
   size_t sizeInBytes,
   wchar_t wchar 
errno_t _wctomb_s_l(
   int *pRetValue,
   char *mbchar,
   size_t sizeInBytes,
   wchar_t wchar,
   _locale_t locale

[out] pRetValue

The number of bytes, or a code indicating the result.

[out] mbchar

The address of a multibyte character.

[in] sizeInBytes

Size of the buffer mbchar.

[in] wchar

A wide character.

[in] locale

The locale to use.

Zero if successful, an error code on failure.

Error Conditions



Return value





not modified




not modified


too small


not modified

If any of the above error conditions occurs, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, wctomb returns EINVAL and sets errno to EINVAL.

The wctomb_s function converts its wchar argument to the corresponding multibyte character and stores the result at mbchar. You can call the function from any point in any program.

If wctomb_s converts the wide character to a multibyte character, it puts the number of bytes (which is never greater than MB_CUR_MAX) in the wide character into the integer pointed to by pRetValue. If wchar is the wide-character null character (L'\0'), wctomb_s fills pRetValue with 1. If the target pointer mbchar is NULL, wctomb_s puts 0 in pRetValue. If the conversion is not possible in the current locale, wctomb_s puts –1 in pRetValue.

wctomb_s uses the current locale for locale-dependent information; _wctomb_s_l is identical except that it uses the locale passed in instead. For more information, see Locale.


Required header





For additional compatibility information, see Compatibility in the Introduction.

This program illustrates the behavior of the wctomb function.

// crt_wctomb_s.cpp
#include <stdio.h>
#include <stdlib.h>

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

    printf_s( "Convert a wide character:\n" );
    wctomb_s( &i, pmb, MB_CUR_MAX, wc );
    printf_s( "   Characters converted: %u\n", i );
    printf_s( "   Multibyte character: %.1s\n\n", pmb );
Convert a wide character:
   Characters converted: 1
   Multibyte character: a

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

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