函数返回类对象的各种形式

来源：互联网发布：增值税税金计算器软件编辑：程序博客网时间：2024/06/05 20:53
/*参数都用引用，不会调用拷贝构造。返回引用不会调用拷贝构造。同时，拷贝构造深拷贝，赋值重载深拷贝。注意对象在栈上，有生命周期，拷贝栈上的对象，需要深拷贝。*/#define _CRT_SECURE_NO_WARNINGS#include<iostream>using namespace std;class MyString{public:char *p;int size;MyString() :size(0),p(nullptr){cout << "call MyString1" << endl;}MyString(char *str){cout << "call MyString2" << endl;p = new char[strlen(str) + 1];size = strlen(str) + 1;strcpy(p, str);}//MyString(MyString &my)//拷贝构造基于引用构造 ，浅拷贝//{//cout << "call 浅拷贝" << endl;//this->p = my.p;//this->size = my.size;//}MyString(MyString & my)//深拷贝{cout << "call 深拷贝" << endl;this->size = my.size;this->p = new char[this->size];strcpy(this->p, my.p);  //副本机制，返回值会调用拷贝构造}//加法重载 MyString operator +(MyString &my){MyString temp; //自动消亡，会调用析构函。temp.size = this->size + my.size;temp.p = new char[temp.size];strcpy(temp.p, this->p);strcat(temp.p, my.p);return temp;}void operator =(MyString &my){cout << "赋值重载" << endl;this->size = my.size;this->p = new char[this->size];strcpy(this->p, my.p);}~MyString(){cout << "call delete" << endl;delete[] p;}};void main(){MyString str1("123");//MyString str1 = "123";MyString str2 = "abc"; MyString temp = str1 + str2;//MyString temp = str1 + str2;分步解析 其中 “=”：为赋值重载//1：MyString temp：会调用构造//2:str1+str2:会调用重载（+）//3:重载时又有返回值，会调用拷由构造，因为拷贝构造有个临时对象所以有个栈的消亡cout << temp.p << endl;MyString temp2;temp2 = str1 + str2; //赋值重载，这时赋值重载也必须深拷贝...//重载 ：void operator =(MyString &my)函数。cout << temp2.p << "  " << temp2.size << endl;/*1：MyString temp = str1 + str2;  //先赋值重载，再拷贝构造2：MyString temp;temp = str1 + str2;//赋值重载*/cin.get();}
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