wcsrtombs - Man Page

convert a wide-character string to a character string (restartable)


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 <wchar.h>

size_t wcsnrtombs(char *restrict dst, const wchar_t **restrict src,
    size_t nwc, size_t len, mbstate_t *restrict ps);
size_t wcsrtombs(char *restrict dst, const wchar_t **restrict src,
    size_t len, mbstate_t *restrict ps);


For wcsrtombs(): 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 wcsrtombs() function shall convert a sequence of wide characters from the array indirectly pointed to by src into a sequence of corresponding characters, beginning in the conversion state described by the object pointed to by ps. If dst is not a null pointer, the converted characters shall then be stored into the array pointed to by dst. Conversion continues up to and including a terminating null wide character, which shall also be stored. Conversion shall stop earlier in the following cases:


When a code is reached that does not correspond to a valid character


When the next character would exceed the limit of len total bytes to be stored in the array pointed to by dst (and dst is not a null pointer)

Each conversion shall take place as if by a call to the wcrtomb() function.

If dst is not a null pointer, the pointer object pointed to by src shall be assigned either a null pointer (if conversion stopped due to reaching a terminating null wide character) or the address just past the last wide character converted (if any). If conversion stopped due to reaching a terminating null wide character, the resulting state described shall be the initial conversion state.

If ps is a null pointer, the wcsrtombs() function shall use its own internal mbstate_t object, which is initialized at program start-up to the initial conversion state. Otherwise, the mbstate_t object pointed to by ps shall be used to completely describe the current conversion state of the associated character sequence.

The wcsnrtombs() and wcsrtombs() functions need not be thread-safe if called with a NULL ps argument.

The wcsnrtombs() function shall be equivalent to the wcsrtombs() function, except that the conversion is limited to the first nwc wide characters.

The wcsrtombs() function shall not change the setting of errno if successful.

The behavior of these functions shall be affected by the LC_CTYPE category of the current locale.

The implementation shall behave as if no function defined in System Interfaces volume of POSIX.1-2017 calls these functions.

Return Value

If conversion stops because a code is reached that does not correspond to a valid character, an encoding error occurs. In this case, these functions shall store the value of the macro [EILSEQ] in errno and return (size_t)-1; the conversion state is undefined. Otherwise, these functions shall return the number of bytes in the resulting character sequence, not including the terminating null (if any).


These functions shall fail if:


A wide-character code does not correspond to a valid character.

These functions may fail if:


ps points to an object that contains an invalid conversion state.

The following sections are informative.



Application Usage




Future Directions


See Also

mbsinit(), wcrtomb()

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

Referenced By

mbsinit(3p), wchar.h(0p), wcrtomb(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual