删除list c ++中的最后3个元素

Question

我有这个c ++代码可以正常删除列表的最后3个元素,但我想知道这是否是正确的方法来做这样的事情,因为我担心删除迭代器问题的元素.代码基本上采用6个元素"Groups"的列表,将其分为2个较小的列表"Group1"和"Group2",然后将不同的List"GroupToCompare"与"Group2"进行比较,如果它们相等,则删除最后一个"团体"的3个要素.

#include "pch.h"
#include <iostream>
#include <iostream>
#include <string>
#include <list>
using namespace std;

int main()
{
    std::list <string> Groups = {};
    Groups = { "Spike", "Jet", "Faye", "Edward", "Vincent", "Elektra" };
    std::list<string> Group1 = {};
    std::list<string> Group2 = {};
    std::list<string> GroupToCompare = {};
    GroupToCompare = { "Edward", "Vincent", "Elektra" };

    size_t half1 = Groups.size() / 2;
    std::list<std::string>::iterator ig = Groups.begin();
    advance(ig, half1);
    Group1.insert(Group1.end(), Groups.begin(), ig);
    Group2.insert(Group2.end(), ig, Groups.end());

    std::list<std::string>::iterator removeIt = Groups.begin();
    advance(removeIt, half1);

    cout << "List Elements 1: " << endl;
    std::list<string>::iterator itrofList = Group1.begin();
    string firstvar;
    for (itrofList = Group1.begin(); itrofList != Group1.end(); ++itrofList) {
        firstvar = *itrofList;
        cout << "Item: " << firstvar << endl;
    }

    cout << "List Elements 2: " << endl;
    std::list<string>::iterator itrofList1 = Group2.begin();
    string firstvar1;
    for (itrofList1 = Group2.begin(); itrofList1 != Group2.end(); ++itrofList1) {
        firstvar1 = *itrofList1;

        cout << "Item: " << firstvar1 << endl;
    }

    if (Group2 == GroupToCompare) {
        removeIt = Groups.erase(removeIt);
        removeIt = Groups.erase(removeIt);
        removeIt = Groups.erase(removeIt);
    }

    cout << "List Elements of Groups after removing the last 3 elements: " << endl;
    std::list<string>::iterator itrofList2 = Groups.begin();
    string firstvar2;
    for (itrofList2 = Groups.begin(); itrofList2 != Groups.end(); ++itrofList2) {
        firstvar2 = *itrofList2;

        cout << "Item: " << firstvar2 << endl;
    }


}

有没有更正确的方法,以防我想删除列表末尾的更多元素,并避免删除迭代器的问题？提前致谢!

Answer 1

即使std::list::erase()多次使用返回的位置调用,调用正确的重载也有助于提高可读性和性能:

iterator erase( iterator first, iterator last );

例:

std::list<int> l{1, 2, 3, 4, 5};
l.erase(std::prev(l.end(), 3), l.end());
// l is {1, 2}

注意:原样,如果l大小不是3 ,则此代码会显示未定义的行为.