将元素添加到抽象类的std :: vector

问题描述：

我想将从一个公共接口（抽象类）派生的类的对象存储在该抽象类的std :: vector中。这个向量应该在循环中填充，通常我会调用类的构造函数并将创建的对象推入向量。

I want to store objects of classes derived from a common interface (abstract class) in a std::vector of that abstract class. This vector should be filled in a loop and usually I would call the constructor of a class and push the created object into the vector.

据我了解，抽象类我只能存储指向该类的指针，因此需要派生类的push_back指针。但是，我不确定这些新创建对象的范围。

As I understand, in case of an abstract class I can only store pointers to that class, so I need to push_back pointers of the derived classes. However, I am not sure about the scope of these newly created objects.

请查看下面的代码。这段代码可以编译并正常工作，但是我的问题是：

Please, have a look at the code below. This code compiles and works fine but my questions are:

a）是否保证对象存在于主函数的第二个for循环中？还是它们会在创建循环的范围之外停止存在？

a) Are the objects guaranteed to exist in the second for-loop in the main function? Or might they cease existing beyond the scope of the loop in which they are created?

b）是否调用了所有对象的析构函数，否则可能会发生内存泄漏？

b) Are all objects' destructors called or might there be memory leaks?

#include<vector>
#include<iostream>
class Interface {
    public:
    Interface( int y ) : x(y) {}
    virtual ~Interface() {}
    virtual void f() = 0;
    int x;  
};

class Derived_A : public Interface {
    public:
    Derived_A( int y ) : Interface(y) {}
    void f(){ return; }
};

class Derived_B : public Interface {
    public:
    Derived_B( int y ) : Interface(y) {}
    void f(){ return; }
};


int main()
{
    std::vector<Interface*> abstractObjects;
    int N = 5;
    for(int ii = 0; ii < N; ii++ )
    {
        abstractObjects.push_back( new Derived_A(ii) );
        abstractObjects.push_back( new Derived_B(ii) );
    }

    for(int ii = 0; ii < abstractObjects.size(); ii++ )
    {
        abstractObjects[ii]->f();
        std::cout << abstractObjects[ii]->x << '\t' << std::endl;
    }


    for(int ii = 0; ii < abstractObjects.size(); ii++ )
    {
        delete abstractObjects[ii];
    }

    return 0;
}

答

智能指针。您可以将指针存储在 unique_ptr 中是RAII类型。当 unique_ptr 超出范围时，它将自动为您删除内存。

This is a perfect case for smart pointers. You can store the pointers in a unique_ptr which is a RAII type. When the unique_ptr goes out of scope it will autmaticlly delete the memory for you.

    //...
    std::vector<std::unique_ptr<Interface>> abstractObjects;
    int N = 5;
    for(int ii = 0; ii < N; ii++ )
    {
        abstractObjects.push_back( std::make_unique<Derived_A>(ii) );
        abstractObjects.push_back( std::make_unique<Derived_B>(ii) );
    }

    for(auto & e : abstractObjects)  // ranged based for loop
    {
        e->f();
        std::cout << e->x << '\t' << std::endl;
    }
    // no need to do anything here.  the vector will get rid of each unique_ptr and each unique_ptr will delete each pointer
    return 0;
}

将元素添加到抽象类的std :: vector

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