wcstombs_s, _wcstombs_s_l

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

#define BUFFER_SIZE 100

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

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

    // Conversion
    wcstombs_s(&i, pMBBuffer, (size_t)BUFFER_SIZE, 
               pWCBuffer, (size_t)BUFFER_SIZE );

    // Output
    printf("   Characters converted: %u\n", i);
    printf("    Multibyte character: %s\n\n",
     pMBBuffer );

    // Free multibyte character buffer
    if (pMBBuffer)
    {
    free(pMBBuffer);
    }
}