mbsrtowcs man page

mbsnrtowcs, mbsrtowcs — convert a character string to a wide-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 mbsnrtowcs(wchar_t *restrict dst, const char **restrict src,
    size_t nmc, size_t len, mbstate_t *restrict ps);
size_t mbsrtowcs(wchar_t *restrict dst, const char **restrict src,
    size_t len, mbstate_t *restrict ps);


For mbsrtowcs(): 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.1-2008 defers to the ISO C standard.

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


A sequence of bytes is encountered that does not form a valid character.


len codes have been stored into 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 mbrtowc() 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 character) or the address just past the last character converted (if any). If conversion stopped due to reaching a terminating null character, and if dst is not a null pointer, the resulting state described shall be the initial conversion state.

If ps is a null pointer, the mbsrtowcs() 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 mbsnrtowcs() function shall be equivalent to the mbsrtowcs() function, except that the conversion of characters pointed to by src is limited to at most nmc bytes (the size of the input buffer).

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 this volume of POSIX.1-2008 calls these functions.

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

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

Return Value

If the input conversion encounters a sequence of bytes that do not form a valid character, an encoding error occurs. In this case, these functions shall store the value of the macro [EILSEQ] in errno and shall return (size_t)-1; the conversion state is undefined. Otherwise, these functions shall return the number of characters successfully converted, not including the terminating null (if any).


These functions shall fail if:


An invalid character sequence is detected.

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

iconv(), mbrtowc(), mbsinit()

The Base Definitions volume of POSIX.1-2008, <wchar.h>

Referenced By

iconv(3p), mbrtowc(3p), mbsinit(3p), wchar.h(0p).

2013 IEEE/The Open Group POSIX Programmer's Manual