Reverse a string in-place in C++

This post provides an overview of some of the available alternatives to reverse a string in-place in C++ using simple for-loop, iterators, and std::reverse algorithm.

1. Using simple for-loop

A simple solution is to loop through the first half of the given string using a simple for-loop and swap the current character with the corresponding character on the other half of the string using STL’s std::swap algorithm.

#include <iostream>

#include <string>

#include <algorithm>

using namespace std;

// Function to reverse a string in-place in C++

void reverse(string &s)

{

int n = s.length();

for (int i = 0; i < n/2; i++) {

std::swap(s[i], s[n-i-1]);

}

int main()

{

std::string s("Reverse a string in C++");

reverse(s);

cout << s;

return 0;

}

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2. Using Iterators

We can avoid iterating with indices with the help of iterators. The reverse algorithm can be implemented as follows using iterators:

#include <iostream>

#include <string>

#include <algorithm>

using namespace std;

// Function to reverse a string in-place in C++

void reverse(string &s)

{

int n = s.length();

std::string::iterator start = s.begin();

std::string::iterator end = s.end();

while (std::distance(start, end) > 0) {

std::swap(*(start++), *(--end));

}

int main()

{

std::string s("Reverse a string in C++");

reverse(s);

cout << s;

return 0;

}

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3. Using `std::reverse` function

Finally, the recommended option is to use the standard algorithm std::reverse from the C++ Standard Library, which can in-place reverse a range of a string or the whole string.

#include <iostream>

#include <string>

#include <algorithm>

using namespace std;

// Function to reverse a string in-place in C++

void reverse(string &s) {

reverse(s.begin(), s.end());

}

int main()

{

std::string s("Reverse a string in C++");

reverse(s);

cout << s;

return 0;

}

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That’s all about reversing a string in-place in C++.

Reverse a string in-place in C++

1. Using simple for-loop

2. Using Iterators

3. Using std::reverse function

3. Using `std::reverse` function