Remove elements from a vector that fulfill a predicate in C++

This post will discuss how to remove elements from a vector that fulfill a predicate in C++.

1. Using Erase-remove idiom

The standard solution to conditionally remove elements from a vector in C++ is using the Erase-remove idiom technique. The name goes after the erase() and remove() functions, since std::remove does not actually remove elements from the underlying container but expects a call to the std::vector::erase algorithm to actually remove elements. For example,

#include <iostream>

#include <vector>

#include <algorithm>

#include <iterator>

int main()

{

std::vector<int> v = {1, 2, 3, 4, 5};

// delete even elements from the vector

v.erase(std::remove_if(v.begin(), v.end(), [](const int& x) {

return x % 2 == 0;

}), v.end());

// print vector contents to std::cout

std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));

return 0;

}

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Output:

1 3 5

2. Using `std::erase_if`

Starting with C++20, we can use the std::erase_if algorithm that erases all elements from the vector satisfying the supplied predicate. It is defined in header <vector> and simplifies the Erase-remove idiom.