如何在C++中創建派生類

Question

我對如何處理C++中的繼承感到困惑

我想在構造函數上傳遞參數。但是當我創建一個沒有參數的類時，我只能運行這個。

這個小程序：

#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); 
    } 

}; 

當編譯我得到的錯誤：

$ 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

構造不會從Shape繼承。你需要爲Rectangle提供一個構造函數，可以利用這個參數簽名：

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