The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
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wcsrtombs - convert a wide-character string to a character string (restartable)


#include <wchar.h>

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


[CX] [Option Start] 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 IEEE Std 1003.1-2001 defers to the ISO C standard. [Option End]

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:

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 implementation shall behave as if no function defined in this volume of IEEE Std 1003.1-2001 calls wcsrtombs().

[CX] [Option Start] If the application uses any of the _POSIX_THREAD_SAFE_FUNCTIONS or _POSIX_THREADS functions, the application shall ensure that the wcsrtombs() function is called with a non-NULL ps argument. [Option End]

The behavior of this function shall be affected by the LC_CTYPE category of the current locale.


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


The wcsrtombs() function may fail if:

[CX] [Option Start] ps points to an object that contains an invalid conversion state. [Option End]
A wide-character code does not correspond to a valid character.

The following sections are informative.










mbsinit(), wcrtomb(), the Base Definitions volume of IEEE Std 1003.1-2001, <wchar.h>


First released in Issue 5. Included for alignment with ISO/IEC 9899:1990/Amendment 1:1995 (E).

Issue 6

In the DESCRIPTION, a note on using this function in a threaded application is added.

Extensions beyond the ISO C standard are marked.

The DESCRIPTION is updated to avoid use of the term "must" for application requirements.

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

End of informative text.

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