c++ issue with function overloading in an inherite

问题:

This is possibly a noob question, sorry about that. I faced with a weird issue recently when trying to mess around with some high level stuff in c++, function overloading and inheritance.

I'll show a simple example, just to demonstrate the problem;

There are two classes, classA and classB, as below;

class classA{
    public:
        void func(char[]){};    
};

class classB:public classA{ 
    public:
        void func(int){};
};

According to what i know classB should now posses two func(..) functions, overloaded due to different arguments.

But when trying this in the main method;

int main(){
    int a;
    char b[20];
    classB objB;
    objB.func(a);    //this one is fine
    objB.func(b);    //here's the problem!
    return 0;
}

It gives errors as the method void func(char[]){}; which is in the super class, classA, is not visible int the derived class, classB.

How can I overcome this? isn't this how overloading works in c++? I'm new to c++ but in Java, i know I can make use of something like this.

Though I've already found this thread which asks about a similar issues, I think the two cases are different.

回答1:

All you need is a using:

class classB:public classA{ 
    public:
        using classA::func;
        void func(int){};
};

It doesn't search the base class for func because it already found one in the derived class. The using statement brings the other overload into the same scope so that it can participate in overload resolution.

回答2:

It is well explained for example in this question's answers:

Why should I use the "using" keyword to access my base class method?

In short, compiler will stop searching for matching methods from parent classes, when it finds matching method name in current class, even when that method is not compatible. I guess this allows some automatic type conversions to work more logically, without needing to override so many parent class methods.

回答3:

If you override one variant of a function in the derived class, you need to override all variants. You can either use what JLledo suggested or write the variant of the function in the derived class which simply calls the base class's function of same signature.

class classA{
    public:
        void func(char[]){};    
};

class classB:public classA{ 
    public:
        void func(int){};
        void func(char[]){};
};

void classB:func(char[] ch)
{
    classA::func(ch);
}

回答4:

You must pass the argument of type int in

objB.func(b);    //here's the problem!

bcs it has been overloaded with int argument