C library - strstr() function

---

---

The C library strstr() function returns a pointer to the first index of a specified substring in another string. The main goal of strstr() is to search for a substring within a larger string and it helps to find the first occurrence of a specified substring.

Syntax

Following is the syntax of the C library strstr() function −

 char *strstr (const char *str_1, const char *str_2); 

Parameters

This function takes two parameters −

• str_1 − This is a main string.

• str_2 − The substring to be searched in main string i.e. str_1.

Return Value

The function return the value based on following conditions −

• The function returns a pointer to the first characters of str_2 in str_1 or null pointer if str_2 is not found in str_1.

• If str_2 is found as an empty string, str_1 is returned.

Example 1

Following is the C library program that demonstrates the substring presence within a main string using the function strstr().

 #include <stdio.h> #include <string.h> int main () { const char str[20] = "TutorialsPoint"; const char substr[10] = "Point"; char *ret; // strstr(main_string, substring) ret = strstr(str, substr); // Display the output printf("The substring is: %s\n", ret); return(0); } 

Output

On execution of code, we get the following result −

 The substring is: Point 

Example 2

Here, we demonstrate how to search the substring within a main string using the strstr() function.

 #include <stdio.h> #include <string.h> int main() { char str_1[100] = "Welcome to Tutorialspoint"; char *str_2; str_2 = strstr(str_1, "ials"); printf("\nSubstring is: %s", str_2); return 0; } 

Output

The above code produces the following result −

 Substring is: ialspoint 

Here, first four characters represents substring from a given string.

Example 3

Below the example set the if-else condition to check whether the substring present in the main string or not.

 #include <stdio.h> #include <string.h> int main(){ char str[] = "It is better to live one day as a King"; char target[] = "live"; char *p = strstr(str, target); if (p) printf("'%s' is present in the given string \"%s\" at position %ld", target, str, p-str); else printf("%s is not present \"%s\"", target, str); return 0; } 

Output

After executing the code, we get the following result −

 'live' is present in the given string "It is better to live one day as a King" at position 16