strstr() Function In C

strstr() Function In C

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C programming language provides the strstr() function which is used to search a string in a string. The first occurrence of the string location is returned as a pointer location. This operation is also called searching a needle in a haystack. The search operation ends with the end of the string which consists of \0 terminating characters. The strstr() function is provided via the <string.h> header.

strstr() Function Syntax

The syntax of the strstr() function syntax is like below. There are two parameters where the first parameter is the text we want to search the SEARCH_TERM inside it.

char *strstr(const char *STRING, const char *SEARCH_TERM)
  • *STRING is the string we want to search. It is a character pointer which is also called as string type.
  • *SEARCH_TERM is the term we will search in STRING.

The strstr() function returns the char pointer for the first match for the specified SEARCH_TERM. If there is no match a null pointer is returned.

Search String

We will search the string I like wisetut.com for the search term wise . As this string contains the search term a character pointer where the wise start will be returned.

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


int main () {
   const char str[] = "I like wisetut.com";
   const char search_term[] = "wise";
   char *result;

   result = strstr(str, search_term);

   printf("The substring is: %s\n", result);
   
   return(0);
}

The output is like below.

The substring is: wisetut.com

Search String At The End Of Line

The strstr() function can be used to search a string at the end of the line. A string can be consist of multiple lines and the end of line characters are \n . So in the following example, we will search the com at the end of the line.

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


int main () {
   const char str[] = "I like wisetut.com\nI like linuxtect.com\nI like pythotect.com";
   const char search_term[] = "com\n";
   char *result;

   result = strstr(str, search_term);

   printf("The substring is: %s\n", result);
   
   return(0);
}

Check If the Specified String Exist

The strstr() function can be used to check if the specified search term exists for the specified string. If the specified SEARCH_TERM does not exist a null pointer is returned which means the SEARCH_TERM does not exist in the specified STRING. We can check the return value if it is null or not for search term existace.

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


int main () {
   const char str[] = "I like wisetut.com\nI like linuxtect.com\nI like pythotect.com";
   const char search_term[] = "commm\n";
   char *result;

   result = strstr(str, search_term);

   if(result){
      printf("The substring is: %s\n", result);
   }else{
      printf("The specified search term does not exist");
   }
   
   return(0);
}

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