function finds the start of the first occurrence
of the substring needle of length needlelen in the memory
area haystack of length haystacklen.
function returns a pointer to the beginning of the
substring, or NULL if the substring is not found.
This function is a GNU extension.
This function was broken in Linux libraries up to and including libc 5.0.9;
there the needle and haystack arguments were interchanged,
and a pointer to the end of the first occurrence of needle
Both old and new libc's have the bug that if needle is empty,
haystack-1 (instead of haystack) is returned.
And glibc 2.0 makes it worse, returning a pointer to the
last byte of haystack.
This is fixed in glibc 2.1.