c++ - 如何删除 C++ 映射中的键值对？

Question

我正在从事一个需要唯一键和值的项目，因此我决定使用 map 。对于有人可能想要更改键值的情况，一切正常。我不确定为什么，但它会导致碎片错误。我不能这样做吗？

void Journal::set_id(int id){               // journal class
    if(join.count(id)){                     // join is: static map <int,string> join
        cout<<"Journal ID is already being used. Try again."<<endl;
    }
    else {
        join.erase (join.find(id));
        join.insert(pair<int,string>(id,name));
    }
}

Answer 1

你的逻辑有问题。

void Journal::set_id(int id){
    if(join.count(id)){
        cout<<"Journal ID is already being used. Try again."<<endl;
    }
    else {
        // When you hit this block of the code, there is nothing
        // in the map corresponding to 'id'.
        // join.find(id) returns the same iterator as join.end()
        // Calling erase() with that iterator is causing you the
        // problem.

        // Don't call erase. Just insert the new item.
        // join.erase (join.find(id));
        join.insert(pair<int,string>(id,name));
    }
}