C++赋值函数+移动赋值函数+移动构造函数详解

int a=10;
int* b=&a;// b为右值。
*b=20;// b为右值，*b为左值。

int a = 10;
&a = 40; //错误：赋值操作要求一个左值
int* b = &(a + 1); //错误：‘&'运算符要求一个左值，a为左值，但a+1为右值。
int* c = &a; //正确：var是左值

int global = 10;
int test()
{
return global;// 返回右值
}
int main()
{
test() = 20;// error，右值不可赋值！
cout << "test为："<<test();
return 0;
}

int global = 10;
int& test()
{
return global;// 返回左值
}
int main()
{
test() = 20;// 左值可赋值
cout << "test为："<<test();
return 0;
}

int a1=20; //非常量左值
const int a2=20; //常量左值
const int a3=20; //常量左值

//非常量左值引用
int &b1=a1; //正确，a1是一个非常量左值，可以被非常量左值引用绑定
int &b2=a2; //错误,a2是一个常量左值，不可以被非常量左值引用绑定
int &b3=20; //错误，10是一个非常量右值，不可以被非常量左值引用绑定
int &b4=a2+a3; //错误,（a2+a3）是一个常量右值，不可以被非常量左值引用绑定

//常量左值引用
const int &c1=a1; //正确，a1是一个非常量左值，可以被非常量右值引用绑定
const int &c2=a2; //正确,a2是一个常量左值，可以被非常量右值引用绑定
const int &c3=a1+a2; //正确，（a1+a2）是一个非常量右值，可以被常量右值引用绑定
const int &c4=a2+a3; //正确,（a2+a3）是一个常量右值，可以被非常量右值引用绑定

Dog(int age,string name) :m_age(new int(age)), m_name(name){}
Dog(Dog& d):m_age(d.m_age),m_name(d.m_name)
{
cout << "我是拷贝构造函数······" << endl;
}
Dog(Dog&& d) :m_age(d.m_age), m_name(d.m_name)
{
d.m_age = nullptr;
cout << "我是移动构造函数······" << endl;
}
int* m_age;
string m_name;#include<string>
#include<iostream>
using namespace std;
class Dog
{
public:
Dog(){};
Dog(int age,string name) :m_age(new int(age)), m_name(name){}
Dog(Dog& d):m_age(d.m_age),m_name(d.m_name)
{
cout << "我是拷贝构造函数······" << endl;
}
Dog(Dog&& d) :m_age(d.m_age), m_name(d.m_name)
{
d.m_age = nullptr;
cout << "我是移动构造函数······" << endl;
}
int* m_age;
string m_name;
};

#include"construct.h"
int main()
{
int age = 19;
string name = "小狗狗";
Dog d1(age, name);
cout << "d1:" <<* d1.m_age << d1.m_name << endl;
Dog d2(move(d1));
bool is = d1.m_age == nullptr;
cout << is << endl;
cout << "d2.age:" << *d2.m_age <<endl<< "d2.name:" <<d2.m_name << endl;
return 0;
}

#include<String>
using namespace std;
class Cat
{
public:
Cat(){}
Cat(int age ,string name):age(age),name(name) {}
Cat& operator=(Cat& c)
{
if (this!= &c)
{
age = c.age;
name = c.name;
}
return *this;
}
int age;
string name;
};

#include"assign.h"
class Dog
{
public:
Dog() {}
Dog(int age, string name) :age(new int(age)), name(name) {}

Dog& operator=(Dog&& c)
{
age = c.age;
name = c.name;
c.age = nullptr;
return *this;
}
int* age;
string name;
};

#include<iostream>
#include"moveAssign.h"
int main()
{
cout << "赋值函数" << endl;
Cat c1(18, "小猫咪");
Cat c2 ;
c2 = c1;
cout << "c1.age:" << c1.age << endl << "c1.name" << c1.name << endl;
cout << "c2.age:" << c2.age << endl << "c2.name" << c2.name << endl<<endl;;
cout << "移动赋值函数" << endl;
Dog d1(19,"小狗狗");
cout << "d1.age:" << *d1.age << endl << "d1.name" << d1.name << endl << endl;
Dog d2;
d2 = move(d1);
bool is = (d1.age == nullptr);
cout << "d1是否为空：" << is << endl;
cout << "d2.age:" << *d2.age << endl << "d2.name" << d2.name << endl;
return 0;
}