WCSTOMBS(3) Linux Programmer's Manual WCSTOMBS(3)
wcstombs - convert a wide-character string to a multibyte string
size_t wcstombs(char *dest, const wchar_t *src, size_t n);
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
3. The wide-character string has been completely converted, including the terminating L'