Remove certain characters from a string in C++

This post will discuss how to remove certain characters from a string in C++.

1. Using `std::remove` function

The recommended approach is to use the std::remove algorithm that takes iterators at the beginning and end of the container and the value to be removed.

#include <iostream>

#include <string>

#include <algorithm>

int main()

{

std::string s = "#Hello #World!!";

std::string chars = "#!";

for (char c: chars) {

s.erase(std::remove(s.begin(), s.end(), c), s.end());

}

std::cout << s;

return 0;

}

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Output:

Hello World

Notice that the Erase-remove idiom technique is used since the std::remove algorithm does not actually remove characters from the string and expects a call to the std::erase algorithm.

2. Using `std::remove_if` function

The above solution makes multiple calls to the std::remove algorithm, one for each given character. Another feasible solution is to use the std::remove_if algorithm that takes a predicate to do the filtering.

#include <iostream>

#include <string>

#include <algorithm>

int main()

{

std::string s = "#Hello #World!!";

std::string chars = "#!";

s.erase(remove_if(s.begin(), s.end(),

[&chars](const char &c) {

return chars.find(c) != std::string::npos;

}),

s.end());

std::cout << s;

return 0;

}

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Output:

Hello World

The above solution calls the string::find function for every character in the given string. Since each call to find() takes linear time, the efficient solution is to insert characters to be removed into a std::unordered_set and call unordered_set::find instead.

That’s all about removing certain characters from a string in C++.

Remove certain characters from a string in C++

1. Using std::remove function

2. Using std::remove_if function

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1. Using `std::remove` function

2. Using `std::remove_if` function