C/string.h/strstr
strstr: Returns a pointer to the first occurrence of *str2 in *str1 or a null pointer if there str2 is not part of str1
//Declaration: char *strstr(const char *str1, const char *str2);
//Return: It returns a null pointer if no match is found.
#include <string.h>
#include <stdio.h>
int main(void)
{
char *p;
p = strstr("this is a test", "is");
printf(p);
return 0;
}
/*
is is a test*/