C++ 使用迭代器访问 vector 的指针元素

Question

使用下面显示的代码，我创建了 4 个类(3 个子类和一个父类(super class))，每个类都具有相同的 print_info() 函数。我已经从每个类创建了指针对象，并将它们插入到使用父类(super class)创建的 vector 中。

#include <iostream>
#include <string>
#include <vector>
#include <iterator>

using namespace std;

class Vehicle
{
    private:
        int wheels, max_speed;
        string model;
    public:
        virtual void print_info()
        {
             cout << "This is function print_info() in Vehicle (parent class)" << endl; 
        }
};

class Car: public Vehicle
{
    private:
        int doors, passengers;
    public:
        void print_info()
        {
             cout << "This is function print_info() in Car (child class)" << endl;
        }
};

class Bike: public Vehicle
{
    private:
        string owner;
        bool hasLights;
    public:
        string my_owner();
};

class Truck: public Vehicle
{
    private:
        float cargo_weight;
        int allowed_speed;
    public:
        void print_info()
        {
            cout << "This is function print_info() in Truck (child class)" << endl;
        }
};

int main()
{
    Vehicle *v1 = new Vehicle();
    Vehicle v2;
    Car c1;
    Car c2;
    Bike b1;
    Truck t1;
    Truck t2;

    vector <Vehicle> vvec;
    Vehicle *v = new Vehicle();
    Car *c = new Car();
    Bike *b = new Bike();
    Truck *t = new Truck();
    vvec.push_back(*v);
    vvec.push_back(*c);
    vvec.push_back(*b);
    vvec.push_back(*t);

    vector<Vehicle>::iterator iter = vvec.begin();
    while( iter != vvec.end()) 
    {
        iter->print_info();
        iter++;
    }

    v1 = &v2;
    v1->print_info();
    v1 = &c2;
    v1->print_info();
    v1 = &t2;
    v1->print_info();
    system("pause");

    return 0;
}

想要的输出是这样的:

这是Vehicle(父类)中的函数print_info

这是 Car(子类)中的函数 print_info

这是Vehicle(父类)中的函数print_info

这是 Truck(子类)中的函数 print_info

这是Vehicle(父类)中的函数print_info

这是 Car(子类)中的函数 print_info

这是 Truck(子类)中的函数 print_info

相反，我得到:

这是Vehicle(父类)中的函数print_info

这是Vehicle(父类)中的函数print_info

这是Vehicle(父类)中的函数print_info

这是Vehicle(父类)中的函数print_info

这是Vehicle(父类)中的函数print_info

这是 Car(子类)中的函数 print_info

这是 Truck(子类)中的函数 print_info

我认为这是由于早期绑定(bind)造成的，但我不知道如何解决!

Answer 1

您需要创建指针 vector vector <Vehicle*> vvec; , 当你 push_back 喜欢 vvec.push_back(*v);您按值传递元素并将其转换为 Vehicle , 因此不会存在多态性，因为 vector 的所有元素都只是简单的 Vehicle 对象，更改为:

//...
vector <Vehicle*> vvec;

Vehicle *v = new Vehicle();
Car *c = new Car();
Bike *b = new Bike();
Truck *t = new Truck();
vvec.push_back(v);
vvec.push_back(c);
vvec.push_back(b);
vvec.push_back(t);

vector<Vehicle*>::iterator iter = vvec.begin();
while( iter != vvec.end())
{
    (*iter)->print_info();
    iter++;
}
//...

你的输出将是:

This is function print_info() in Vehicle (parent class)
This is function print_info() in Car (child class)
This is function print_info() in Vehicle (parent class)
This is function print_info() in Truck (child class)
This is function print_info() in Vehicle (parent class)
This is function print_info() in Car (child class)
This is function print_info() in Truck (child class)