wcstombs, _wcstombs_l

Converts a sequence of wide characters to a corresponding sequence of multibyte characters. More secure versions of these functions are available; see wcstombs_s, _wcstombs_s_l.

Syntax

size_t wcstombs(
   char *mbstr,
   const wchar_t *wcstr,
   size_t count
);
size_t _wcstombs_l(
   char *mbstr,
   const wchar_t *wcstr,
   size_t count,
   _locale_t locale
);
template <size_t size>
size_t wcstombs(
   char (&mbstr)[size],
   const wchar_t *wcstr,
   size_t count
); // C++ only
template <size_t size>
size_t _wcstombs_l(
   char (&mbstr)[size],
   const wchar_t *wcstr,
   size_t count,
   _locale_t locale
); // C++ only

Parameters

mbstr
The address of a sequence of multibyte characters.

wcstr
The address of a sequence of wide characters.

count
The maximum number of bytes that can be stored in the multibyte output string.

locale
The locale to use.

Return value

If wcstombs successfully converts the multibyte string, it returns the number of bytes written into the multibyte output string, excluding the terminating NULL (if any). If the mbstr argument is NULL, wcstombs returns the required size in bytes of the destination string. If wcstombs encounters a wide character it can't convert to a multibyte character, it returns -1 cast to type size_t and sets errno to EILSEQ.

Remarks

The wcstombs function converts the wide-character string pointed to by wcstr to the corresponding multibyte characters and stores the results in the mbstr array. The count parameter indicates the maximum number of bytes that can be stored in the multibyte output string (that is, the size of mbstr). In general, it isn't known how many bytes will be required when converting a wide-character string. Some wide characters will require only a single byte in the output string; others require 2 bytes. If there are 2 bytes in the multibyte output string for every wide character in the input string (including the wide character NULL), the result is guaranteed to fit.

Starting in Windows 10 version 1803 (10.0.17134.0), the Universal C Runtime supports using a UTF-8 code page. Use wcstombs(NULL, wcstr, 0) to get the correct size that you'll need for the conversion because assuming that you'll need two bytes for every wide character may not be enough. For more information about UTF-8 support, see UTF-8 support

If wcstombs encounters the wide-character NULL character (L'\0') either before or when count occurs, it converts it to an 8-bit 0 and stops. Thus, the multibyte character string at mbstr is null-terminated only if wcstombs encounters a wide-character NULL character during conversion. If the sequences pointed to by wcstr and mbstr overlap, the behavior of wcstombs is undefined.

If the mbstr argument is NULL, wcstombs returns the required size in bytes of the destination string.

wcstombs validates its parameters. If wcstr is NULL, or if count is greater than INT_MAX, this function invokes the invalid parameter handler, as described in Parameter validation. If execution is allowed to continue, the function sets errno to EINVAL and returns -1.

wcstombs uses the current locale for any locale-dependent behavior; _wcstombs_l is identical except that it uses the locale passed in instead. For more information, see Locale.

In C++, these functions have template overloads that invoke the newer, secure counterparts of these functions. For more information, see Secure template overloads.

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

Requirements

Routine	Required header
wcstombs	<stdlib.h>
_wcstombs_l	<stdlib.h>

For more compatibility information, see Compatibility.

Example

This program illustrates the behavior of the wcstombs function.

// crt_wcstombs.c
// compile with: /W3
// This example demonstrates the use
// of wcstombs, which converts a string
// of wide characters to a string of
// multibyte characters.

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

#define BUFFER_SIZE 100

int main( void )
{
    size_t  count;
    char    *pMBBuffer = (char *)malloc( BUFFER_SIZE );
    wchar_t *pWCBuffer = L"Hello, world.";

    printf("Convert wide-character string:\n" );

    count = wcstombs(pMBBuffer, pWCBuffer, BUFFER_SIZE ); // C4996
    // Note: wcstombs is deprecated; consider using wcstombs_s instead
    printf("   Characters converted: %u\n",
            count );
    printf("    Multibyte character: %s\n\n",
           pMBBuffer );

    free(pMBBuffer);
}

Convert wide-character string:
   Characters converted: 13
    Multibyte character: Hello, world.

See also

Data conversion
Locale
_mbclen, mblen, _mblen_l
mbstowcs, _mbstowcs_l
mbtowc, _mbtowc_l
wctomb, _wctomb_l
WideCharToMultiByte