Replace all occurrences of a character in string in C++

This post will discuss how to replace all occurrences of a character in a string with another character in C++.

1. Using `std::string::replace` function

The string class doesn’t provide any function to replace all occurrences of a character in a string with another character. The best you can do is repeatedly call std::string::replace until all matching characters are replaced with the help of std::string::find, as shown below:

#include <iostream>

#include <string>

int main()

{

std::string s = "C**";

std::string x = "*", y = "+";

size_t pos;

while ((pos = s.find(x)) != std::string::npos) {

s.replace(pos, 1, y);

}

std::cout << s;

return 0;

}

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Output:

C++

This solution is recommended only if the total number of characters to be replaced m are minimal compared to the length of the string n, i.e., m << n.

The worst-case time complexity of this approach is O(n²), where n is the length of the string. The worst-case happens when all characters in the string are the same as the specified character and the find() function executes n times. The best case O(n) happens when the input string doesn’t have a single occurrence of the given character.

2. Using `std::replace` function

The recommended solution is to use the standard algorithm std::replace from the <algorithm> header. It does one linear scan of the string and in-place replaces all the matching characters.

#include <iostream>

#include <algorithm>

#include <string>

int main()

{

std::string s = "C**";

const char x = '*';

const char y = '+';

std::replace(s.begin(), s.end(), x, y);

std::cout << s;

return 0;

}

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Output:

C++

3. Using Boost Library

If you’re using the boost in your project, you can go with the boost::replace_all algorithm, as shown below:

#include <iostream>

#include <string>

#include <boost/algorithm/string/replace.hpp>

int main()

{

std::string s = "C**";

std::string x = "*", y = "+";

boost::replace_all(s, x, y);

std::cout << s;

return 0;

}

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Output:

C++

That’s all about replacing all occurrences of a character in string in C++.

Replace all occurrences of a character in string in C++

1. Using std::string::replace function

2. Using std::replace function

3. Using Boost Library

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1. Using `std::string::replace` function

2. Using `std::replace` function