set容器运用迭代器删除数据

Question

#include<set>
#include<algorithm>
#include<iostream>
using namespace std;

void myPrint(char c)
{
    cout << c << " ";
}
int main()
{
    set<char>s1;
    for (int i = 97; i < 107; i++)
    {
        s1.insert((char)i);
    }
    if (!s1.empty())
    {
        cout << "容器不为空" << endl;
        cout << "容器的大小是" << endl << s1.size() << endl;
        for_each(s1.begin(), s1.end(), myPrint); cout << endl;
    }
    else
        cout << "容器为空" << endl;

    set<char>s2;
    for (int i = 65; i < 73; i++)
    {
        s2.insert((char)i);
    }


    cout << "容器交换前" << endl;
    for_each(s1.begin(), s1.end(), myPrint); cout << endl;
    for_each(s2.begin(), s2.end(), myPrint); cout << endl;

    cout << "容器交换后" << endl;
    s1.swap(s2);
    for_each(s1.begin(), s1.end(), myPrint); cout << endl;
    for_each(s2.begin(), s2.end(), myPrint); cout << endl;

        s1.swap(s2);
    cout << "删除第二个元素b" << endl;
    s1.erase(++s1.begin());
    for_each(s1.begin(), s1.end(), myPrint); cout << endl;

    cout << "删除第三、四个元素de" << endl;
    //为啥这么写没什么效果
    set<char>::iterator it1=++(++s1.begin()) ;
    set<char>::iterator it2=++(it1) ;
    s1.erase(it1,it2);
    for_each(s1.begin(), s1.end(), myPrint); cout << endl;

    cout << "删除j" << endl;
    s1.erase('j');
    for_each(s1.begin(), s1.end(), myPrint); cout << endl;

    cout << "清空" << endl;
    s1.clear();
    for_each(s1.begin(), s1.end(), myPrint); cout << endl;
}

Answer 1

因为

set<char>::iterator it2=++(it1);

it1 本身也在自增，这时候 it2 = it1，所以没变化

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如果有用麻烦点个采纳，谢谢~