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。
- 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;
}
- 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;
}
- 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 memory
delete s;
}