NAME

mbstowcs — convert a character string to a wide-character string

SYNOPSIS

#include <stdlib.h>

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


DESCRIPTION

^[CX] 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.1-2024 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. ^[XSI]  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 ^[CX]  and shall set errno to indicate the error.

Otherwise, mbstowcs() shall return the number of the array elements modified ^[XSI]  (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.

ERRORS

The mbstowcs() function shall fail if:

[EILSEQ]

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

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

mblen, mbtowc, wctomb, wcstombs

XBD <stdlib.h>

CHANGE HISTORY

First released in Issue 4. Aligned with the ISO C standard.

Issue 6

The mbstowcs() prototype is updated for alignment with the ISO/IEC 9899:1999 standard.

Extensions beyond the ISO C standard are marked.

Issue 7

Austin Group Interpretation 1003.1-2001 #170 is applied.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0371 [195] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0208 [663,674] is applied.