wcsnrtombs is like wcsrtombs, except that the number of wide characters to be converted, starting at src, is limited to nwc.
If dest is not a NULL pointer, wcsnrtombs converts at most nwc wide characters from the wide-character string src to a multibyte string starting at dest. At most len bytes are written to dest. The state ps is updated.
The conversion is effectively performed by repeatedly calling:
wcrtomb(dest, *src, ps)
The conversion can stop for three reasons:
A wide character has been encountered that cannot be represented as a multibyte sequence (according to the current locale). In this case src is left pointing to the invalid wide character, (size_t)(-1) is returned, and errno is set to EILSEQ.
nws wide characters have been converted without encountering a L'\0', or the length limit forces a stop. In this case, src is left pointing to the next wide character to be converted, and the number bytes written to dest is returned.
The wide-character string has been completely converted, including the terminating L'\0' (which has the side effect of bringing back ps to the initial state). In this case, src is set to NULL, and the number of bytes written to dest, excluding the terminating '\0' byte, is returned.
If dest is NULL, len is ignored, and the conversion proceeds as above, except that the converted bytes are not written out to memory, and that no destination length limit exists.
In both of the above cases, if ps is a NULL pointer, a static anonymous state only known to wcsnrtombs is used instead.
The programmer must ensure that there is room for at least len bytes at dest.
wcsnrtombs returns the number of bytes that make up the converted part of multibyte sequence, not including the terminating NULL byte. If a wide character was encountered which could not be converted, (size_t)(-1) is returned, and the global variable errno set to EILSEQ.
The behavior of wcsnrtombs depends on the LC_CTYPE category of the current locale.
Passing NULL as ps is not multi-thread safe.