深入C++中構(gòu)造函數(shù)、拷貝構(gòu)造函數(shù)、賦值操作符、析構(gòu)函數(shù)的調(diào)用過程總結(jié)

來源：本站原創(chuàng)|時(shí)間：2020-01-10|欄目：C語言|點(diǎn)擊：次

1 . 用同一個(gè)類的源對(duì)象構(gòu)造一個(gè)目標(biāo)對(duì)象時(shí)，會(huì)調(diào)用拷貝構(gòu)造函數(shù)來構(gòu)造目標(biāo)對(duì)象，如果沒有定義拷貝構(gòu)造函數(shù)，將調(diào)用類的默認(rèn)拷貝函數(shù)來構(gòu)造目標(biāo)對(duì)象。
2 . 當(dāng)一個(gè)函數(shù)的返回值為一個(gè)類的對(duì)象時(shí)，如果在調(diào)用函數(shù)中，沒有定義一個(gè)對(duì)象來接收這個(gè)返回對(duì)象值，會(huì)用返回一個(gè)臨時(shí)對(duì)象保存返回對(duì)象的值。在被調(diào)用函數(shù)結(jié)束時(shí)，這個(gè)臨時(shí)對(duì)象被銷毀。而當(dāng)調(diào)用函數(shù)中有一個(gè)接受對(duì)象時(shí)，就將返回對(duì)象賦值給接收對(duì)象，這個(gè)返回對(duì)象在調(diào)用函數(shù)結(jié)束時(shí)調(diào)用析構(gòu)函數(shù)。
3. 當(dāng)類有一個(gè)帶有一個(gè)參數(shù)的構(gòu)造函數(shù)時(shí)，可以用這個(gè)參數(shù)同類型的數(shù)據(jù)初始化這個(gè)對(duì)象，默認(rèn)會(huì)調(diào)用這個(gè)構(gòu)造函數(shù)。

復(fù)制代碼代碼如下:

    #include "stdafx.h"  
    #include <iostream>  
    using namespace std;  
    class B  
    {  
    public:  
        B():data(0)    //默認(rèn)構(gòu)造函數(shù)  
        {   
            cout << "Default constructor is called." << endl;  
        }  
        B(int i):data(i) //帶參數(shù)的構(gòu)造函數(shù)  
        {  
            cout << "Constructor is called." << data << endl;  
        }  
        B(B &b)   // 復(fù)制（拷貝）構(gòu)造函數(shù)  
        {  
            data = b.data; cout << "Copy Constructor is called." << data << endl;  
        }  
        B& operator = (const B &b) //賦值運(yùn)算符的重載  
        {  
            this->data = b.data;  
            cout << "The operator \"= \" is called." << data << endl;  
            return *this;  
        }  
        ~B() //析構(gòu)函數(shù)  
        {  
            cout << "Destructor is called. " << data << endl;  
        }  
    private:  
        int data;  
    };  

    //函數(shù)，參數(shù)是一個(gè)B類型對(duì)象，返回值也是一個(gè)B類型的對(duì)象  
    B fun(B b)  
    {  
        return b;  
    }  

    //測試函數(shù)  
    int _tmain(int argc, _TCHAR* argv[])  
    {  
        fun(1);  
        cout << endl;  

        B t1 = fun(2);  
        cout << endl;  

        B t2;  
        t2 = fun(3);  

        return 0;  
    }  

復(fù)制代碼代碼如下:

輸出結(jié)果為：

復(fù)制代碼代碼如下:

    Constructor is called.1             //用1構(gòu)造參數(shù)b     
    Copy Constructor is called.1      //用b拷貝構(gòu)造一個(gè)臨時(shí)對(duì)象，因?yàn)榇藭r(shí)沒有對(duì)象來接受fun的返回值     
    Destructor is called. 1            //參數(shù)b被析構(gòu)     
    Destructor is called. 1             //臨時(shí)對(duì)象被析構(gòu)  
    Constructor is called.2                  //用2構(gòu)造參數(shù)b        
    Copy Constructor is called.2           //用b拷貝構(gòu)造t1，此時(shí)調(diào)用的是拷貝構(gòu)造函數(shù)     
    Destructor is called. 2                  //參數(shù)b被析構(gòu)  
    Default constructor is called.             //調(diào)用默認(rèn)的構(gòu)造函數(shù)構(gòu)造t2        
    Constructor is called.3                       //用3構(gòu)造參數(shù)b        
    Copy Constructor is called.3             //用b拷貝構(gòu)造一個(gè)臨時(shí)對(duì)象        
    Destructor is called. 3                        //參數(shù)b被析構(gòu)        
    The operator "= " is called.3              //調(diào)用=操作符初始化t2，此時(shí)調(diào)用的是賦值操作符     
    Destructor is called. 3                         //臨時(shí)對(duì)象被析構(gòu)        
    Destructor is called. 3                         //t2被析構(gòu)        
    Destructor is called. 2                         //t1被析構(gòu)        
    請(qǐng)按任意鍵繼續(xù). . .  