C String Functions - C strstr

strstr() function takes two strings as arguments and searches the first string for an occurrence of the second string.

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

Finds the first occurrence of the entire string str2 which appears in the string str1.

Returns a pointer to the first occurrence of str2 in str1.

If no match was found, then a null pointer is returned.

If str2 points to a string of zero length, then the argument str1 is returned.

Prototype

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

Parameter

This function has the following parameter.

str1: C string to be scanned.
str2: C string containing the sequence of characters to match.

Return

A pointer to the first occurrence in str1 of the characters specified in str2, or a null pointer if the sequence is not present in str1.

Example


#include <stdio.h>
#include <string.h>
/*from w  w  w .ja  v a 2 s. c  o m*/
int main (){
  char str[] ="This is a simple string";
  char * pch;
  pch = strstr (str,"simple");
  strncpy (pch,"sample",6);
  puts (str);
  return 0;
}

The code above generates the following result.

Example 2


#include <stdio.h> 
#include <string.h> 
main() { //w  w w .j  av a 2  s. co  m
   char *str1 = "this is a testing xyz"; 
   char *str2 = "ing"; 
   char *str3 = "xyz"; 

   printf("\nstr1 = %s\n", str1); 
   printf("\nstr2 = %s\n", str2); 
   printf("\nstr3 = %s\n", str3);  

   if ( strstr(str1, str2) != NULL ) 
     printf("\nstr2 was found in str1\n"); 
   else 
     printf("\nstr2 was not found in str1\n"); 

   if ( strstr(str1, str3) != NULL ) 
     printf("\nstr3 was found in str1\n"); 
   else 
     printf("\nstr3 was not found in str1\n"); 
}

The code above generates the following result.

Example 3


#include <string.h>
#include <stdio.h>
 /*from   w ww  . ja va  2s.com*/
void find_str(char const* str, char const* substr) {
    char* pos = strstr(str, substr);
    if(pos) {
        printf("found the string '%s' in '%s' at position: %ld\n", substr, str, pos - str);
    } else {
        printf("the string '%s' was not found in '%s'\n", substr, str);
    }
}
 
int main(void) 
{
    char* str = "one two three";
    find_str(str, "two");
    find_str(str, "");
    find_str(str, "java2s.com");
    find_str(str, "n");
    return 0;
}

The code above generates the following result.