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man pages section 3: Basic Library Functions

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Updated: July 2017



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,
     size_t len, mbstate_t *restrict ps);


The mbsrtowcs() function converts 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 are stored into the array pointed to by dst. Conversion continues up to and including a terminating null character, which is also stored. Conversion stops early in either of the following cases:

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

  • When len codes have been stored into the array pointed to by dst (and dst is not a null pointer).

Each conversion takes place as if by a call to the mbrtowc() function.

If dst is not a null pointer, the pointer object pointed to by src is 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 is the initial conversion state.

If ps is a null pointer, the mbsrtowcs() function uses its own internal mbstate_t object, which is initialized at program startup to the initial conversion state. Otherwise, the mbstate_t object pointed to by ps is used to completely describe the current conversion state of the associated character sequence. Solaris will behave as if no function defined in the Solaris Reference Manual calls mbsrtowcs().

The behavior of this function is affected by the LC_CTYPE category of the current locale. See environ(5).

Return Values

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 returns (size_t)−1 ; the conversion state is undefined. Otherwise, it returns the number of characters successfully converted, not including the terminating null (if any).


The mbsrtowcs() function may fail if:


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


Invalid character sequence is detected.


See attributes(5) for descriptions of the following attributes:

Interface Stability
See NOTES below

See Also

mbrtowc(3C), mbsinit(3C), setlocale(3C), attributes(5), environ(5), standards(5)


If ps is not a null pointer, mbsrtowcs() uses the mbstate_t object pointed to by ps and the function can be used safely in multithreaded applications, as long as setlocale(3C) is not being called to change the locale. If ps is a null pointer, mbsrtowcs() uses its internal mbstate_t object and the function is Unsafe in multithreaded applications.