The interface __wmempcpy_chk() shall function in the same way as the interface wmempcpy(), except that __wmempcpy_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 ns1 specifies the size of the object pointed to by s1. If n exceeds ns1, the function shall abort and the program calling it shall exit.
The __wmempcpy_chk() function is not in the source standard; it is only in the binary standard.