`wcrtomb`

บทความ
02/09/2023

Convert a wide character into its multibyte character representation. A more secure version of this function is available; see wcrtomb_s.

Syntax

size_t wcrtomb(
   char *mbchar,
   wchar_t wchar,
   mbstate_t *mbstate
);
template <size_t size>
size_t wcrtomb(
   char (&mbchar)[size],
   wchar_t wchar,
   mbstate_t *mbstate
); // C++ only

Parameters

mbchar
The resulting multibyte converted character.

wchar
A wide character to convert.

mbstate
A pointer to an mbstate_t object.

Return value

Returns the number of bytes required to represent the converted multibyte character, otherwise a -1 if an error occurs.

Remarks

The wcrtomb function converts a wide character, beginning in the specified conversion state contained in mbstate, from the value contained in wchar, into the address represented by mbchar. The return value is the number of bytes required to represent the corresponding multibyte character, but it will not return more than MB_CUR_MAX bytes.

If mbstate is null, the internal mbstate_t object containing the conversion state of mbchar is used. If the character sequence wchar doesn't have a corresponding multibyte character representation, a -1 is returned, and the errno is set to EILSEQ.

The wcrtomb function differs from wctomb, _wctomb_l by its restartability. The conversion state is stored in mbstate for subsequent calls to the same or other restartable functions. Results are undefined when mixing the use of restartable and nonrestartable functions. For example, an application would use wcsrlen rather than wcsnlen, if a subsequent call to wcsrtombs were used instead of wcstombs.

In C++, this function has a template overload that invokes the newer, secure counterparts of this function. 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.

Exceptions

The wcrtomb function is multithread safe as long as no function in the current thread calls setlocale while this function is executing and while the mbstate is null.

Example

// crt_wcrtomb.c
// compile with: /W3
// This program converts a wide character
// to its corresponding multibyte character.

#include <string.h>
#include <stdio.h>
#include <wchar.h>

int main( void )
{
    size_t      sizeOfCovertion = 0;
    mbstate_t   mbstate;
    char        mbStr = 0;
    wchar_t*    wcStr = L"Q";

    // Reset to initial conversion state
    memset(&mbstate, 0, sizeof(mbstate));

    sizeOfCovertion = wcrtomb(&mbStr, *wcStr, &mbstate); // C4996
    // Note: wcrtomb is deprecated; consider using wcrtomb_s instead
    if (sizeOfCovertion > 0)
    {
        printf("The corresponding wide character \"");
        wprintf(L"%s\"", wcStr);
        printf(" was converted to the \"%c\" ", mbStr);
        printf("multibyte character.\n");
    }
    else
    {
        printf("No corresponding multibyte character "
               "was found.\n");
    }
}

The corresponding wide character "Q" was converted to the "Q" multibyte character.

Requirements

Routine	Required header
`wcrtomb`	<wchar.h>

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