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What is strstr() Function in C language?
The C library function char *strstr(const char *haystack, const char *needle) function finds the first occurrence of the substring needle in the string haystack. The terminating '\0' characters are not compared.
An array of characters is called a string.
Declaration
The syntax for declaring an array is as follows −
char stringname [size];
For example − char string[50]; string of length 50 characters
Initialization
- Using single character constant −
char string[10] = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’ ,‘\0’}- Using string constants −
char string[10] = "Hello":;
Accessing − There is a control string "%s" used for accessing the string till it encounters ‘\0’.
The strstr() Function
It is used to search whether a substring is present in the main string or not.
It returns pointer to first occurrence of s2 in s1.
Syntax
The syntax for strstr() function is as follows −
strstr(mainsring,substring);
Example
The following program shows the usage of strstr() function.
#include<stdio.h>
void main(){
char a[30],b[30];
char *found;
printf("Enter a string:
");
gets(a);
printf("Enter the string to be searched for:
");
gets(b);
found=strstr(a,b);
if(found)
printf("%s is found in %s in %d position",a,b,found-a);
else
printf("-1 since the string is not found");
}Output
When the above program is executed, it produces the following result −
Enter a string: how are you Enter the string to be searched for: you you is found in 8 position
Example 2
Let’s see another program on strstr() function.
Given below is a C program to find, if a string is present in another string as substring by using strstr library function −
#include<stdio.h>
#include<string.h>
void main(){
//Declaring two strings//
char mainstring[50],substring[50];
char *exists;
//Reading strings//
printf("Enter the main string :
");
gets(mainstring);
printf("Enter the sub string you would want to check if exists in main string :");
gets(substring);
//Searching for sub string in main string using library function//
exists = strstr(mainstring,substring);
//Conditions//
if(exists){
printf("%s exists in %s ",substring,mainstring);
} else {
printf("'%s' is not present in '%s'",substring,mainstring);
}
}Output
When the above program is executed, it produces the following result −
Enter the main string : TutorialsPoint c Programming Enter the sub string you would want to check if exists in main string :Programming Programming exists in TutorialsPoint c Programming
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