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`strstr'--find string segment

     #include <string.h>
     char *strstr(const char *S1, const char *S2);
Locates the first occurence in the string pointed to by S1 of the
sequence of characters in the string pointed to by S2 (excluding the
terminating null  character).
Returns a pointer to the located string segment, or a null pointer if
the string S2 is not found. If S2 points to a string with zero length,
the S1 is returned.
`strstr' is ANSI C.
   `strstr' requires no supporting OS subroutines.