如何在 C++ 中创建派生 class

Question

我对如何在 C++ 中处理继承感到困惑

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class时，我只得到了运行。

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);
    }

};

编译时出现错误：

$ 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

构造函数不是从 Shape 继承的。您需要为 Rectangle 提供构造函数，它可以采用此参数签名：

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

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