Fast std::vector removal when order is not a priority

c++ tricks

fastVecErase.cpp

#include <iostream>
#include <memory>
#include <vector>
#include <chrono>
#include <ctime>
#include <algorithm>

 
struct Foo
{
    int i;
    std::string str;
    Foo(int _i, std::string _str) : i(_i), str(_str) {}
    Foo(Foo&& _other) : i(std::move(_other.i)), str(std::move(_other.str)) {}
    Foo operator=(Foo&& _other) {
        i = std::move(_other.i);
        str = std::move(_other.str);
        return std::move(*this);
    }
};

int main() {

    std::vector<Foo> vec1;
    std::vector<Foo> vec2;

    for(int i = 0; i < 2000; i++) {
        vec1.push_back(Foo(i%500, "blah"));
        vec2.push_back(Foo(i%500, "blah"));
    }

    auto start = std::clock();
    for(auto itr = vec1.begin(); itr != vec1.end(); ) {
        if(itr->i == 400) {
            //std::cout<<itr->i<<"\n";
            *itr = std::move(vec1[vec1.size()-1]);
            //std::cout<<itr->i<<"\n";
            vec1.pop_back();
        }
        itr++;
    }
    auto end = std::clock();

    for(auto itr = vec2.begin(); itr != vec2.end(); ) {
        if(itr->i == 400) {
            itr = vec2.erase(itr);
        } else {
            itr++;
        }
        
    }

    auto finish = std::clock();

    std::cout<<"sizeof vec1: "<<vec1.size()<<"\ttime used: "<<1000.0 * (end - start) / CLOCKS_PER_SEC<<"\n";
    std::cout<<"sizeof vec2: "<<vec2.size()<<"\ttime used: "<<1000.0 * (finish - end) / CLOCKS_PER_SEC;

    return 0;
}