C++ cstring strstr() Function

The C++ cstring strstr() Function is used to find the first occurrence of a sub-string in the current string.

This is similar to the strchr(), but the difference is that strchr() finds the first occurrence of a character in a string whereas, the strstr() function finds the first occurrence of a substring in a string.

Now, let's take an example where you have a DSA question and you need to find the first occurrence of the word 'question' in the string. In this case, you can use the strstr() function.

Syntax

Following is the syntax of the strstr() function −

char *strstr(const char *str1, const char *str2);

Parameters

Parameters of the strstr() function are as follows −

• str1: This is the pointer to the string where the search is performed.
• str2: This is the pointer to the substring to be located.

Return Value

The strstr() function returns a pointer to the first occurrence of the substring str2 in the string str1, or a null pointer if the substring is not found.

Example 1

Following example demonstrates the basic usage of the C++ cstring strstr() function −

Here, we will take a string str and then search for the first occurrence of the substring 'point' in the string using the strstr() function.

#include <iostream>
#include <cstring>
using namespace std;

int main() {
   char str[] = "tutorialspoint";
   char substr[] = "point";
   char *ret;

   ret = strstr(str, substr);

   if(ret) {
      cout << "Substring found: " << ret << endl;
   } else {
      cout << "Substring not found" << endl;
   }
   return 0;
}

Output

Following is the output of the above C++ program:

Substring found: point

Example 2

Now, let's take another example where we will search for the substring that is not present in the string.

For this, we will take a string str and then search for the first occurrence of the substring 'xyz' in the string using the strstr() function.

#include <iostream>
#include <cstring>
using namespace std;

int main() {
   char str[] = "tutorialspoint";
   char substr[] = "xyz";
   char *ret;

   ret = strstr(str, substr);

   if(ret) {
      cout << "Substring found: " << ret << endl;
   }else {
      cout << "Substring not found" << endl;
   }
   return 0;
}

Output

Following is the output of the above C++ program −

Substring not found