strchr() function in C++ and its applications

In C++, strchr() is a predefined function used for finding the occurrence of a character in a string. It is present in cstring header file.

Syntax:

// Returns pointer to the first occurrence
// of c in str[]
char *strchr(const char *str, int c) 

Note that c is passed as its int promotion, but it is internally treated as char.
Application
Given a string in c++, we need to find the first occurrence of a character, let’s say ‘a’. 

Examples: 

Input : str[] = ‘This is a string’
Output : 9

Input : str[] = ‘My name is Ayush’
Output : 5

Algorithm:
1. Pass the given string in the strchr() function and mention the character you need to point. 
2. The function returns a value, and print the value.

Below is the implementation of the above algorithm:

CPP

// CPP program to find position of a character
// in a given string.
#include <iostream>
#include <cstring>
using namespace std;

int main()
{
    char str[] = "My name is Ayush";
    char* ch = strchr(str, 'a');
    cout << ch - str + 1;
    return 0;
}

Output

5

strchr() function can also be used to check the presence of a character in a string. The input consists of a character we want to check, if it exists in the string. 
Example:  Let’s check if the characters A and z are present in the string – “My name is Ayush” 

Input : str[] = ‘My name is Ayush’, 
        ch1 = ‘A’, ch2 = ‘z’
Output : A is present in the string
         z is not present in the string

Algorithm
1. Pass the given string in the strchr() function with the character as the second parameter and check if the value returned is not null 
2. If the function returns a NULL value, this means that the string does not contain the character, so, print the required statement. 
3. Else if the function does not returns a NULL value, this means that the string contains the character, so, print the required statement.

Below is the implementation of the above algorithm:

CPP

// CPP program to demonstrate working of strchr()
#include <iostream>
#include <cstring>
using namespace std;
// Driver code
int main()
{
    char str[] = "My name is Ayush";
    char ch = 'A', ch2 = 'z';
    if (strchr(str, ch) != NULL)
        cout << ch << " "
             << "is present in string" << endl;
    else
        cout << ch << " "
             << "is not present in string" << endl;
    if (strchr(str, ch2) != NULL)
        cout << ch2 << " "
             << "is present in string" << endl;
    else
        cout << ch2 << " "
             << "is not present in string" << endl;
    return 0;
}

Output

A is present in string
z is not present in string

strrchr() in C++

The strrchr() function is a similar function to strchr() but this function returns the pointer to the last occurrence of the given character in the string.

Applications:

Some of the application of strrchr() is:

strchr() function can be used to find absolute directory path for Linux: (Contributed by Ekta_nehwal)

Examples:

Input : /home/test/sample
Output : /home/test

Algorithm:

1. Find the position of last “/” in the directory path by using strrchr.
2. Replace the occurrence with the NULL character.

Below is the implementation of the above algorithm, basically we are finding the position of / and then changing it to \0(null).

C

// C program to find directory path
#include <string.h>
#include<stdio.h>

int main()
{
   char string[]={"/home/test/sample"};
   int len;

    //position of last char
    char* pos;

    // save length of string
    len = strlen(string);

    // Find the last character with
    pos = strrchr(string,'/') ;
    printf("%s\n",string);

    // replace last occurrence of / with NULL character.
    *pos='\0';
    printf("%s\n",string);

    return 0;
}

Output

/home/test/sample
/home/test

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