If dest is not a NULL pointer, the wcstombs function converts the
wide-character string src to a multibyte string starting at
dest. At most n bytes are written to dest. The conversion
starts in the initial state. 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
(size_t)(-1) is returned.
2. The length limit forces a stop. In this case the number of bytes written to
dest is returned, but the shift state at this point is lost.
3. The wide-character string has been completely converted, including the
terminating L'\0'. In this case the conversion ends in the initial state. The
number of bytes written to dest, excluding the terminating '\0' byte,
The programmer must ensure that there is room for at least n bytes at
If dest is NULL, n 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 order to avoid the case 2 above, the programmer should make sure n is
greater or equal to wcstombs(NULL,src,0)+1.
The wcstombs 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)