构造函数、拷贝构造函数、赋值函数、析构函数的调用顺序

例1 

#include "stdafx.h"#include <iostream>#include <assert.h>using namespace std;class B{public:B(){cout<<"default constructor\n";}~B(){cout<<"destructed\n";}B(int i):data(i){cout<<"constructed by parameter"<<data<<endl;}B(B &b){cout<<"copy constructor\n";data=b.data;}protected:private:int data;};B play(B b){return b;}int _tmain(int argc, _TCHAR* argv[]){B t1=play(5);B t2=play(t1);system("pause");return 0;}

输出结果：

 constructed by parameter 5
 copy constructor
 destructed
 copy constructor
 copy constructor
 destructed
 destructed
 destructed

 

分析：

 constructed by parameter 5        调用带参数的构造函数在play内产生临时对象
 copy constructor      调用复制构造函数把临时对象复制到t1
 destructed         play内的临时对象析构
 copy constructor     调用复制构造函数在play内产生临时对象
 copy constructor   调用复制构造函数把临时对象复制到t2
 destructed     play内的临时对象析构
 destructed    t2析构
 destructed   t1析构

 

 

 

例2

 

#include "stdafx.h"#include <iostream>#include <assert.h>using namespace std;class B{public:B(){cout<<"default constructor\n";}~B(){cout<<"destructed\n";}B(int i):data(i){cout<<"constructed by parameter"<<data<<endl;}B(B &b){cout<<"copy constructor\n";data=b.data;}protected:private:int data;};B play(B b){return b;}int _tmain(int argc, _TCHAR* argv[]){B t1=play(5);B t2=play(10);system("pause");return 0;}

输出结果：

constructed by parameter 5
 copy constructor
 destructed
 constructed by parameter 10
 copy constructor
 destructed
 destructed
 destructed

分析：

constructed by parameter 5     调用带参数的构造函数play内产生临时对象
 copy constructor      调用复制构造函数把临时对象复制到t1
 destructed            play内临时对象析构
 constructed by parameter 10       调用带参数的构造函数play内产生临时对象
 copy constructor        调用复制构造函数把临时对象复制到t2
 destructed       play内临时对象析构
 destructed     t2析构
 destructed    t1析构

 

例3

#include "stdafx.h"#include <iostream>#include <assert.h>using namespace std;class B{public:B(){cout<<"default constructor\n";}~B(){cout<<"destructed\n";getchar();}B(int i){cout<<"constructed by parameter"<<endl;}B(B &b){cout<<"copy constructor\n";getchar();}B& operator =(const B&b){cout<<"This is an assigment function\n";return *this;}protected:private:};B play(){B b;return b;}int _tmain(int argc, _TCHAR* argv[]){B b;b=play();return 0;}

输出：

default constructor
 default constructor
 copy constructor
 destructed
 This is an assigment function
 destructed
 destructed

 

分析：

default constructor  main()函数中的对象a通过默认构造函数创建
 default constructor    play()函数中的对象a通过默认构造函数创建
 copy constructor   play()返回时生成临时对象是由复制构造函数生成的
 destructed           play()函数中的a对象析构
 This is an assigment function   临时对象赋给a使用赋值函数
 destructed     临时对象析构
 destructed   main()函数中的对象a析构