C++繼承特性

1. 子類不聲明構造函數

#include <iostream>
class Uncopyable {
public:
  Uncopyable();
  ~Uncopyable() {}
  Uncopyable(const Uncopyable&);
  Uncopyable& operator=(const Uncopyable&);
};

Uncopyable::Uncopyable() {
  std::cout << "inherit default constructor\n";
} 

Uncopyable::Uncopyable(const Uncopyable&) {
  std::cout << "inherit copy constructor\n";
}

Uncopyable& Uncopyable::operator=(const Uncopyable&) {
  std::cout << "inherit copy asigment\n";
  return *this;
}

class HomeForSale: private Uncopyable {
};

int main() {
  HomeForSale s1;
  HomeForSale s2(s1);
}

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輸出

inherit default constructor
inherit copy constructor
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子類調用相應的父類構造函數（counterpart）

2.子類聲明構造函數

#include <iostream>
class Uncopyable {
public:
  Uncopyable();
  ~Uncopyable() {}
  Uncopyable(const Uncopyable&);
  Uncopyable& operator=(const Uncopyable&);
};

Uncopyable::Uncopyable() {
  std::cout << "inherit default constructor\n";
} 

Uncopyable::Uncopyable(const Uncopyable&) {
  std::cout << "inherit copy constructor\n";
}

Uncopyable& Uncopyable::operator=(const Uncopyable&) {
  std::cout << "inherit copy asigment\n";
  return *this;
}

class HomeForSale: private Uncopyable {
  public:
  HomeForSale();
  HomeForSale(const HomeForSale&);
};

HomeForSale::HomeForSale() {
  std::cout << "HomeForSale default constructor\n";
}

HomeForSale::HomeForSale(const HomeForSale&) {
  std::cout << "HomeForSale copy constructor\n";
}

int main() {
  HomeForSale s1;
  HomeForSale s2(s1);
}

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輸出

inherit default constructor
HomeForSale default constructor
inherit default constructor
HomeForSale copy constructor
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子類調用父類默認構造函數