Different Methods to Reverse a String in C++

The reversing of a string is nothing but simply substituting the last element of a string to the 1st position of the string.

Different Methods to Reverse a String in C++ are:

• Making our own reverse function 
• Using ‘inbuilt’ reverse function 
• Using Constructor
• Using a temp file

1. Making a Custom Reverse Function For Swapping Characters

A. Using a first to last approach ‘for’ loop

CPP

// C++ program to reverse a string
// using first to last approach
// 'for' loop
#include <bits/stdc++.h>
using namespace std;

// Function to reverse a string
void reverseStr(string& str)
{
    int n = str.length();

    // Swap character starting from two
    // corners
    for (int i = 0; i < n / 2; i++)
        swap(str[i], str[n - i - 1]);
}

// Driver program
int main()
{
    string str = "geeksforgeeks";
    reverseStr(str);
    cout << str;
    return 0;
}

Output :

skeegrofskeeg

B. Using a Last to First Approach ‘for‘ Loop  

C++

// C++ program to demonstrate reverse
// of a string using Last to First
// Approach 'for' Loop
#include <bits/stdc++.h>
using namespace std;

// Function to reverse a string
void reverse(string str)
{
    for (int i = str.length() - 1; i >= 0; i--)
        cout << str[i];
}

// Driver code
int main(void)
{
    string s = "GeeksforGeeks";
    reverse(s);
    return (0);
}

Output:

skeegrofskeeG

2. Using the inbuilt “reverse” Function

There is a direct function in the “algorithm” header file for doing reverse that saves our time when programming.

// Reverses elements in [begin, end]
void reverse (BidirectionalIterator begin, 
BidirectionalIterator end);

CPP

// C++ program to illustrate the
// reversing of a string using
// reverse() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
    string str = "geeksforgeeks";

    // Reverse str[begin..end]
    reverse(str.begin(), str.end());

    cout << str;
    return 0;
}

Output:

skeegrofskeeg

3. Reverse a String Using the Constructor 

Passing reverse iterators to the constructor returns us a reversed string. 

CPP

// C++ program to reverse
// string using constructor
#include <bits/stdc++.h>
using namespace std;
int main()
{
    string str = "GeeksforGeeks";

    // Use of reverse iterators
    string rev = string(str.rbegin(), str.rend());

    cout << rev << endl;
    return 0;
}

Output:

skeeGrofskeeG

4. Using a Temporary String

CPP

// C++ program to demonstrate
// reversing of string
// using temporary string
#include <bits/stdc++.h>
using namespace std;
int main()
{

    string str = "GeeksforGeeks";
    int n = str.length();

    // Temporary string to store the reverse
    string rev;

    for (int i = n - 1; i >= 0; i--)
        rev.push_back(str[i]);

    cout << rev << endl;
    return 0;
}

Output:

skeeGrofskeeG

How could we get the reverse of a const string?

To get the reverse of a const string we have to first declare a ‘const string’ in a user-defined function following which we have declared then use the following algorithm for the calling of the desired objects.

“const reverseConstString = function(string) { return string.split("").reverse().join("")” 

Example: 

C++

// C++ program to get reverse of a const string
#include <bits/stdc++.h>
using namespace std;

// Function to reverse string and return
// reverse string pointer of that
char* reverseConstString(char const* str)
{
    // find length of string
    int n = strlen(str);

    // create a dynamic pointer char array
    char* rev = new char[n + 1];

    // copy of string to ptr array
    strcpy(rev, str);

    // Swap character starting from two
    // corners
    for (int i = 0, j = n - 1; i < j; i++, j--)
        swap(rev[i], rev[j]);

    // return pointer of the reversed string
    return rev;
}

// Driver code
int main(void)
{
    const char* s = "GeeksforGeeks";
    printf("%s", reverseConstString(s));
    return (0);
}

Output:

skeeGrofskeeG

This article is contributed by Priyam kakati, Ranju Kumari, Somesh Awasthi. If you like GeeksforGeeks and would like to contribute, you can also write an article at write.geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or if you want to share more information about the topic discussed above.