c++ - 重载函数的调用 - 以继承类作为参数 - 是不明确的

Question

这个标题已被多次使用，但在搜索了大约 5-6 个示例后，我找不到与我的问题相匹配的任何内容:

我有一个简单的继承实践。

A 类是基类，B 和 C 类继承自它:

class A {

};

class B : public A { public:    int i; };

class C : public A { public:    int j; };

还有一个类 P 包含这样的重载函数:

class P
{
public:
    void change(B *b)
    {
        b->i =1;
    }

    void change(C *c)
    {
        c->j =1;
    }
};

当我使用如下函数时:

int main()
{
    A *b = new B();
    A *c = new C();
    P p;
    p.change(b);
    p.change(c);
    return 0;
}

它给出一个错误提示:

inherit2.cpp: In function ‘int main()’:
inherit2.cpp:37:12: error: call of overloaded ‘change(A*&)’ is ambiguous
inherit2.cpp:37:12: note: candidates are:
inherit2.cpp:21:7: note: void P::change(B*) <near match>
inherit2.cpp:21:7: note:   no known conversion for argument 1 from ‘A*’ to ‘B*’
inherit2.cpp:26:7: note: void P::change(C*) <near match>
inherit2.cpp:26:7: note:   no known conversion for argument 1 from ‘A*’ to ‘C*’
inherit2.cpp:38:12: error: call of overloaded ‘change(A*&)’ is ambiguous
inherit2.cpp:38:12: note: candidates are:
inherit2.cpp:21:7: note: void P::change(B*) <near match>
inherit2.cpp:21:7: note:   no known conversion for argument 1 from ‘A*’ to ‘B*’
inherit2.cpp:26:7: note: void P::change(C*) <near match>
inherit2.cpp:26:7: note:   no known conversion for argument 1 from ‘A*’ to ‘C*’

如果你能帮我解决这个问题，我将不胜感激。拉赫曼

Answer 1

Polymorphism is one answer

class A
{
public:
    virtual void set() = 0;
};


class B : public A
{
public:
    virtual void set() { i = 1; }
private:
    int i;
};

class C : public A
{
public:
    virtual void set() { j = 1; }
private:
    int j;
};

class P
{
public:
    void change(A *a)
    {
        a->set();
    }
};

int main()
{
    A *b = new B();
    A *c = new C();
    P p;
    p.change(b);
    p.change(c);
    return 0;
}

有了多态性，就不需要多个change方法。