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