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.
A newer edition of this document exists here


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


#include <wchar.h>

size_t mbsrtowcs(wchar_t *restrict
dst, const char **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 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:

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 implementation behaves as if no function defined in this volume of IEEE Std 1003.1-2001 calls mbsrtowcs().

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


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


The mbsrtowcs() function may fail if:

[CX] [Option Start] ps points to an object that contains an invalid conversion state. [Option End]
Invalid character sequence is detected.

The following sections are informative.










mbsinit(), mbrtowc(), 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

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

The [EINVAL] error condition is marked CX.

End of informative text.

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