If dest is not a NULL pointer, the wcsrtombs function converts the
wide-character string *src to a multibyte string starting at
dest. At most len bytes are written to dest. The shift
state *ps is updated. The conversion is effectively performed by
repeatedly calling wcrtomb( dest,*src,ps), as long as
this call succeeds, and then incrementing dest by the number of bytes
written and *src by one. The conversion can stop for three reasons:
1. A wide character has been encountered that can not 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.
2. The length limit forces a stop. In this case *src is left pointing to
the next wide character to be converted, and the number of bytes written to
dest is returned.
3. 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
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 length limit exists.
In both of the above cases, if ps is a NULL pointer, a static anonymous
state only known to the wcsrtombs function is used instead.
The programmer must ensure that there is room for at least len bytes at
The wcsrtombs function 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 errno set to EILSEQ.