I would use the standard ISO C strstr instead of writing the function they are calling find.
Yes, we had strstr in 1994; it was in the 1989 ANSI C standard.
On a very small system, strstr will probably just be naively coded, to save space. On a big system, it might use Knuth-Morrison-Pratt or Boyer-Moore. I don't have to care; by using strstr, that decision is taken care of.