##### Synopsis

    #include <string.h>
    char *strstr(const char *s1, const char *s2);

##### Description

strstr locates the first occurrence in the string pointed to by s1 of the sequence of characters (excluding the terminating null character) in the string pointed to by s2.
strstr returns a pointer to the located string, or a null pointer if the string is not found. If s2 points to a string with zero length, strstr returns s1.

##### Portability

strstr conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).