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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022



wcrtomb - convert a wide-character code to a character (restartable)


#include <stdio.h>

size_t wcrtomb(char *restrict s, wchar_t wc, mbstate_t *restrict ps);


If s is a null pointer, the wcrtomb() function is equivalent to the call:

wcrtomb(buf, L'\0', ps)

where buf is an internal buffer.

If s is not a null pointer, the wcrtomb() function determines the number of bytes needed to represent the character that corresponds to the wide-character given by wc (including any shift sequences), and stores the resulting bytes in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If wc is a null wide-character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state. The resulting state described is the initial conversion state.

If ps is a null pointer, the wcrtomb() 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 wcrtomb().

The behavior of this function is affected by the LC_CTYPE category of the current locale. See environ(7).

Return Values

The wcrtomb() function returns the number of bytes stored in the array object (including any shift sequences). When wc is not a valid wide-character, an encoding error occurs. In this case, the function stores the value of the macros EILSEQ in errno and returns (size_t)−1; the conversion state is undefined.


The wcrtomb() function may fail if:


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


Invalid wide-character code is detected.


If ps is not a null pointer, wcrtomb() 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, wcrtomb() uses its internal mbstate_t object and the function is Unsafe in multithreaded applications.


See attributes(7) for descriptions of the following attributes:

Interface Stability
See NOTES below

See Also

mbsinit(3C), setlocale(3C), attributes(7), environ(7), standards(7)