c++ - STL 容器，从两个容器中删除对象

Question

假设我有两个容器，保存指向对象的指针，它们共享它们的一些元素。 从 http://www.cplusplus.com/reference/stl/list/erase/ 它说:

This effectively reduces the list size by the number of elements removed, calling each element's destructor before.

如何在不调用析构函数两次的情况下从两个容器中删除一个对象:

例子

#include <map>
#include <string>
using namespace std;
//to lazy to write a class 
struct myObj{
          string pkid;
          string data;
};
map<string,*myObj> container1;
map<string,*myObj> container2;

int main()
{
       myObj * object = new myObj();
       object->pkid="12345";
       object->data="someData";
       container1.insert(object->pkid,object);
       container2.insert(object->pkid,object);

       //removing object from container1
       container1.erase(object->pkid);
       //object descructor been called and container2 now hold invalid pointer

       //this will call try to deallocate an deallocated memory
       container2.erase(object->pkid);

}

请多多指教

Answer 1

如果您的容器持有指针，则不会调用这些对象的析构函数(STL 不会跟随这些指针并调用指针对象的析构函数)。

相反，如果您的容器本身包含全尺寸对象，那么将调用这些对象的析构函数。

您的 map 声明和插入语句中也有一些语法错误。尝试运行以下代码。请注意，析构函数仅被调用一次(对于删除语句)。 永远不会为删除语句调用析构函数。

#include <map>
#include <string>
#include <iostream>
using namespace std;
//to lazy to write a class 
struct myObj{
    ~myObj() {
        cout << "DESTRUCTION" << endl;
    }
          string pkid;
          string data;
};
map<string,myObj*> container1;
map<string,myObj*> container2;

int main()
{
       myObj * object = new myObj();
       object->pkid="12345";
       object->data="someData";
       container1.insert(pair<string,myObj*>(object->pkid,object));
       container2.insert(pair<string,myObj*>(object->pkid,object));

       //removing POINTER from container1
       container1.erase(object->pkid);
       //object's destructor has NOT been called yet

       //removing POINTER from container2
       container2.erase(object->pkid);
       //object's destructor STILL hasn't been called

       delete object;   // DESTRUCTION!
}