Question

我有两个父类P，派生类D和函数show（）。此外，我有一个P对象的数组，并在该数组中我分配从P派生的对象，如D.和我从数组调用show（）函数。但它似乎只调用P空函数，而不是派生重写函数。

我的代码：

//parent.h    

class P
{
public:
    P(){ }
    ~P(){ }

    virtual void show(){ }
};

//derived.h

#include "parent.h"

class D : public P
{
public:
    D(){ }
    ~D(){ }

    void show();
};

//derived.cpp

#include "derived.h"

void D::show()
{
    std::cout<<"Showing Derived Function\n";
}

// main.cpp中

#include "derived.h"
#include <vector>

int main()
{
    vector<P> objectz;

    for(int i=0; i<8; i++)
    {
        D derp;
        objectz.insert(objectz.begin(), derp);
    }

    for(int i=0; i<8; i++)
    {
        objectz[i].show(); //Call it Here !!
    }

    return 0;
}

Answer 1

这可能是因为您没有将数组声明为P指针数组。确保您的数组声明为：

P* elements[ N ];

以下是一些显示多态性的示例代码：

#include <iostream>
#include <cstddef>

struct P
{
    virtual void func() { std::cout << "Parent" << std::endl; }
};

struct D : P
{
    void func() override { std::cout << "Derived" << std::endl; }
};

int main()
{
    const std::size_t N( 2 );

    P* elements[ N ];

    P parent;
    D derived;

    elements[ 0 ] = &parent;
    elements[ 1 ] = &derived;

    for ( std::size_t i( 0 ); i < N; ++i )
        elements[ i ]->func();

    std::cout << "Enter a character to exit: "; char c; std::cin >> c;
    return 0;
}

使用std :: vector：

#include <iostream>
#include <cstddef>
#include <vector>

... // same P and D definitions as in the previous example.

int main()
{
    std::vector<P*> elements; 

    elements.push_back( &P() ); // &P(): create an instance of P and return its address.
    elements.push_back( &D() ); // &D(): create an instance of D and return its address.

    for ( std::vector<P*>::size_type i( 0 ), sz( elements.size() ); i < sz; ++i )
        elements[ i ]->func();

    std::cout << "Enter a character to exit: "; char c; std::cin >> c;
    return 0;
}

从父级调用派生类覆盖函数。 C ++

1 个答案: