constructor1.cpp

ThinkingC++中文版

//: C06:Constructor1.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 2000
// Copyright notice in Copyright.txt
// Constructors & destructors
#include <iostream>
using namespace std;

class Tree {
  int height;
public:
  Tree(int initialHeight);  // Guaranteed initialization with the constructor.Like any function, the constructor can have arguments to allow you to specify how an object is created, give it initialization values, 
  ~Tree();  // Guaranteed cleanup with the destructor
  void grow(int years);
  void printsize();
};

Tree::Tree(int initialHeight) {
  height = initialHeight;
}

Tree::~Tree() {
  cout << "inside Tree destructor" << endl;
  printsize();
}

void Tree::grow(int years) {
  height += years;
}

void Tree::printsize() {
  cout << "Tree height is " << height << endl;
}

void main() {
  cout << "before opening brace" << endl;
  {
    Tree t(12);	//when the program reaches the sequence point (point of execution) where t is defined, the constructor is called automatically. 
    cout << "after Tree creation" << endl;
    t.printsize();
    t.grow(4);
    cout << "before closing brace" << endl;
  }
  cout << "after closing brace" << endl;
} ///:~

//You can see that the destructor is automatically called at the closing brace of the scope that encloses it.