strstr in C

Purpose of strstr()

strstr() is one of the inbuilt string function in c programming which is used to return the first occurrence of the substring str2 in a string str1.

How strstr() Works

The following diagram clearly illustrate the working principle of strstr() inbuilt string function in C.

In the above diagram strstr() takes two strings as a parameters. Here strstr() will search for a string str2 in str1. If it presents it returns str1 starting for str2. If not it returns null.

Syntax - strstr()

• strstr() accepts two parameters.
• Both parameters are string.
• To use strstr() inbuilt string function in C, we need to declare #include<string.h> header file.

strstr(str1, str2);

C Program - strstr()

Let us work through strstr() function, In the following program we will find the first occurrence of the substring str2 in a string str1

#include <stdio.h>
#include<string.h>
int main()
{
char str1[30] = "Learning C is awesome";
char str2 [15] = "C";
char *st;
st = strstr(str1, str2);
printf("%s", st);
return 0;
}

C is awesome

C Program - Without strstr()

Let us find the first occurrence of the substring str2 in a string str1 without using strstr() inbuilt string function.

#include <stdio.h>
#include<string.h>
int main()
{
char str1[30] = "Learing C is awesome";
char str2 [15] = "C";
int i, j, k, m, count = 0;
for(i = 0; str2[i] !='\0'; i++)
{
// to find the length of str2
}
for(j = 0 ; str1[j]!='\0'; j++)
{
if(str1[j] == str2[0])
{
for(k = 0 ; k < i;k++)
{
if(str1[j]==str2[k]){
j++;
count++;
}
}
if(count == i)
{
for(m=j-i; str1[m]!='\0'; m++)
printf("%c",str1[m]);
}
}
}
return 0;
}

C is awesome

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