C ++纯虚方法 [英] C++ pure virtual methods

问题描述

请考虑此演示程序：

#include <stdio.h>

class Base
{
public:
    virtual int f(int) =0;
    virtual int f(){ return f(0); }

    virtual ~Base(){ }
};

class Derived : public Base
{
public:
    int f(int i)
    {
        return (10 + i);
    }
};

int main(void)
{
    Derived obj;
    printf("%d\n", obj.f(1));  // This works, and returns 11
    printf("%d\n", obj.f());   // Adding this line gives me the error listed below
}

编译错误：

virtualfunc.cpp: In function ‘int main()’:
virtualfunc.cpp:25:26: error: no matching function for call to ‘Derived::f()’
virtualfunc.cpp:15:9: note: candidate is: virtual int Derived::f(int)

我希望调用 obj.f（）在调用 Base :: obj.f（），因为派生类没有定义它，这将导致调用 Derived :: obj.f（0）根据Base类中的定义。

My hope was that a call to obj.f() would result in a call to Base::obj.f() since the derived class doesn't define it, which would then result in a call to Derived::obj.f(0) per the definition in class Base.

我在这里做错了什么？有办法做到这一点吗？具体来说，我想调用 obj.f（）返回10。

What am I doing wrong here? Is there a way to accomplish this? Specifically, I'd like the call to obj.f() to return 10.

我认为我可以使用默认参数来解决这个问题，但是这个代码只是一个简单的例子，所以请不要告诉我使用默认参数。）

(Also please note that I realize I could use a default argument to solve this, but this code is simply a concise example of my issue, so please don't tell me to use default arguments.)

感谢。

推荐答案

原因是定义的 f （ Derived ） hides f Base 类。解决方案是使用添加。像这样：

The reason is, that the defined f (in Derived ) hides the f functions from the Base class. The solution is to add using. Like this:

class Derived : public Base
{
public:
    int f(int i)
    {
        return (10 + i);
    }

//  vvvvvvvvvvvvvv
    using Base::f;
};

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