Convert a wide-character string to a multibyte string
#include <wchar.h> size_t wcsrtombs(char *dest, const wchar_t **src, size_t len, mbstate_t *ps);
If dest is not NULL, 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 null wide character (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 null byte ('\0'), 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 length limit exists.
In both of the above cases, if ps is NULL, a static anonymous state known only to the wcsrtombs() function is used instead.
The programmer must ensure that there is room for at least len bytes at dest.
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.
The behavior of wcsrtombs() depends on the LC_CTYPE category of the current locale.
Passing NULL as ps is not multithread safe.
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