mbstowcs - Man Page

convert a character string to a wide-character string


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <stdlib.h>

size_t mbstowcs(wchar_t *restrict pwcs, const char *restrict s,
    size_t n);


The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.

The mbstowcs() function shall convert a sequence of characters that begins in the initial shift state from the array pointed to by s into a sequence of corresponding wide-character codes and shall store not more than n wide-character codes into the array pointed to by pwcs. No characters that follow a null byte (which is converted into a wide-character code with value 0) shall be examined or converted. Each character shall be converted as if by a call to mbtowc(), except that the shift state of mbtowc() is not affected.

No more than n elements shall be modified in the array pointed to by pwcs. If copying takes place between objects that overlap, the behavior is undefined.

The behavior of this function shall be affected by the LC_CTYPE category of the current locale. If pwcs is a null pointer, mbstowcs() shall return the length required to convert the entire array regardless of the value of n, but no values are stored.

Return Value

If an invalid character is encountered, mbstowcs() shall return (size_t)-1 and shall set errno to indicate the error.

Otherwise, mbstowcs() shall return the number of the array elements modified (or required if pwcs is null), not including a terminating 0 code, if any. The array shall not be zero-terminated if the value returned is n.


The mbstowcs() function shall fail if:


An invalid character sequence is detected. In the POSIX locale an [EILSEQ] error cannot occur since all byte values are valid characters.

The following sections are informative.



Application Usage




Future Directions


See Also

mblen(), mbtowc(), wctomb(), wcstombs()

The Base Definitions volume of POSIX.1-2017, <stdlib.h>

Referenced By

ctype.h(0p), mblen(3p), mbtowc(3p), setlocale(3p), stdlib.h(0p), wcstombs(3p), wctomb(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual