C++ 继承具有不同默认参数值的函数

Question

我想继承一个成员函数而不重新定义它，但给它不同的默认值。我该怎么办？

class Base{
  public:
    void foo(int val){value=val;};
  protected:
    int value;
};

class Derived : public Base{
  public:
    void foo(int val=10);
};

class Derived2 : public Base{
  public:
    void foo(int val=20);
};

void main(){
   Derived a;
   a.foo();//set the value field of a to 10
   Derived2 b;
   b.foo();//set the value field of b to 20
}

Answer 1

不要使用默认值，使用重载:

class Base{
    public:
        virtual void foo() = 0;

    protected:
        void foo(int val) { value = val; }

    private:
        int value;
};

class Derived : public Base {
    public:
        void foo() override { Base::foo(10); }
};

class Derived2 : public Base {
    public:
        void foo() override { Base::foo(20); }
};

override 修饰符是 C++11。