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关于隐藏 (hidden)
假如继承以后，子类出现父类同名函数， 即使参数的形式不同， 也会导致父类的函数隐藏， 不参与函数匹配，不能使用。
这个链接讲的不错。https://zhuanlan.zhihu.com/p/575423511

#include <iostream>
using namespace std;
class Vehicle {
public:void accelerate() { cout << "Increasing speed: "; }
};
class Aeroplane : public Vehicle {public:void accelerate(int height) {cout << "Accelerating at a height of: " << height;}
};int main() {Aeroplane plane;plane.accelerate(1000);plane.accelerate();  //这里出错！main.cpp:17:25: error: no matching function for call to ‘Aeroplane::accelerate()’cout << endl;
}

如果子类的instance就是想调用父类的同名不同参的函数呢？方法有两个。

1. 显式调用父类版本的函数
   b.A::func(); // 显式指定父类版本，合法
   #include
   using namespace std;
   class Vehicle {
   public:
   void accelerate() { cout << "Increasing speed: "; }
   };
   class Aeroplane : public Vehicle {
   public:
   void accelerate(int height) {
   cout << "Accelerating at a height of: " << height;
   }
   };

int main() {
Aeroplane plane;
plane.accelerate(1000);
plane.Vehicle::accelerate();
cout << endl;
}

2. 用using
   using A::func; // 解开父类重载函数的默认隐藏。

#include <iostream>
using namespace std;
class Vehicle {
public:void accelerate() { cout << "Increasing speed: "; }
};
class Aeroplane : public Vehicle {public:using Vehicle::accelerate;void accelerate(int height) {cout << "Accelerating at a height of: " << height;}
};int main() {Aeroplane plane;plane.accelerate(1000);plane.accelerate();cout << endl;
}

3. 当然也可以直接在子类的函数里面调用

class Aeroplane : public Vehicle {public:void accelerate(int height) {Vehicle::accelerate();  cout << "Accelerating at a height of: " << height;}
};

关于overload

关于override
如果不用virtual，怎么实现多态呢？可以用cast。但是对不同子类的object都要cast到对应的子类类型，显然很不方便。
static_cast<Circle *>(s)->draw();

#include <iostream>
#include <vector>using namespace std;class Shape {
public:void draw() { cout << "Drawing a generic shape...\n"; }
};class Circle: public Shape {
public:void draw() { cout << "Drawing a circle...\n"; }
};int main() {vector<Shape *> shapes;      // Vector of pointers to Shape instances// Create a pointer to a child class of Shape and append it to the vector shapes.push_back(new Circle);for (auto s: shapes)static_cast<Circle *>(s)->draw();      for (auto s : shapes)       // Release allocated memorydelete s;
}