如何在C++中创建派生类

Question

我对如何处理C++中的继承感到困惑

我想在构造函数上传递参数。但是当我创建一个没有参数的类时，我只能运行这个。

这个小程序：

#include <iostream> 
using namespace std; 

// Base class 

class Shape { 
    protected: 

    int width, height; 

    public: 

    Shape(int w, int h) { 
    width = w; 
    height = h; 
    } 

    void setDimensions(int w, int h) { 
    width = w; 
    height = h; 
    } 

}; 

// New class Rectangle based on Shape class 

class Rectangle: public Shape { 
    public: 

    int getArea() { 
     return (width * height); 
    } 

}; 

当编译我得到的错误：

$ g++ inheritance.cpp -o inheritance -g -std=c++11 
inheritance.cpp:44:13: error: no matching constructor for initialization of 'Rectangle' 
    Rectangle r(3, 4) 
      ^~~~~ 
inheritance.cpp:33:7: note: candidate constructor (the implicit copy constructor) not viable: requires 1 argument, but 2 were provided 
class Rectangle: public Shape { 
    ^
inheritance.cpp:33:7: note: candidate constructor (the implicit move constructor) not viable: requires 1 argument, but 2 were provided 
inheritance.cpp:33:7: note: candidate constructor (the implicit default constructor) not viable: requires 0 arguments, but 2 were provided 

Answer 1

构造不会从Shape继承。你需要为Rectangle提供一个构造函数，可以利用这个参数签名：

Rectangle(int w, int h) : Shape(w,h) { }