The interface __wcsrtombs_chk() shall function in the same way as the interface wcsrtombs(), except that __wcsrtombs_chk() shall check for buffer overflow before computing a result. If an overflow is anticipated, the function shall abort and the program calling it shall exit.
The parameter destlen specifies the size of the object pointed to by dest. If len exceeds destlen, the function shall abort and the program calling it shall exit.
The __wcsrtombs_chk() function is not in the source standard; it is only in the binary standard.