The interface __read_chk() shall function in the same way as the interface read(), except that __read_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 buflen specifies the size of the buffer buf. If nbytes exceeds buflen, the function shall abort, and the program calling it shall exit.
The __read_chk() function is not in the source standard; it is only in the binary standard.