Which of the following function is used to find the first occurrence of a given string in another string?

The function strstr() Finds the first occurrence of a substring in another string

Declaration: char *strstr(const char *s1, const char *s2);

Return Value:
On success, strstr returns a pointer to the element in s1 where s2 begins (points to s2 in s1).
On error (if s2 does not occur in s1), strstr returns null.

Example:

#include <stdio.h>
#include <string.h>

int main(void)
{
   char *str1 = "CuriousTab", *str2 = "ia", *ptr;

   ptr = strstr(str1, str2);
   printf("The substring is: %s\n", ptr);
   return 0;
}

Output: The substring is: iaCURIOUSTAB