C++程序设计方法2：基本语法2

对象赋值-赋值运算符重载

赋值运算符函数是在类中定义的特殊的成员函数

典型的实现方式：

ClassName& operator=(const ClassName &right)
{
    if (this != &right)
    {
　　　　　　//将right的内容复制给当前的对象
    }
    return *this;
}

#include <iostream>
using namespace std;

class Test
{
    int id;
public:
    Test(int i) :id(i) { cout << "obj_" << id << "created\n"; }
    Test& operator= (const Test& right)
    {
        if (this == &right)
            cout << "same obj!" << endl;
        else
        {
            cout << "obj_" << id << "=obj_" << right.id << endl;
            this->id = right.id;
        }
        return *this;
    }
};

int main()
{
    Test a(), b();
    cout << "a = a:";
    a = a;
    cout << "a = b:";
    a = b;
    return ;
}

流运算符重载函数的声明

istream& operator>>(istream& in, Test& dst);

ostream& operator<<(ostream& out, const Test& src);

备注：

函数名为：
　　operaotor>>和operator<<

返回值为：
　　istream& 和ostream&,均为引用

参数分别：流对象的引用，目标对象的引用。对于输出流，目标对象还是常量

#include <iostream>
using namespace std;

class Test
{
    int id;
public:
    Test(int i) :id(i)
    {
        cout << "obj_" << id << "created\n";
    }
    friend istream& operator >> (istream& in, Test& dst);
    friend ostream& operator << (ostream& out, const Test& src);
};
//备注：以下两个流运算符重载函数可以直接访问私有成员，原因是其被声明成了友元函数
istream& operator >> (istream& in, Test& dst)
{
    in >> dst.id;
    return in;
}

ostream& operator << (ostream& out, const Test& src)
{
    out << src.id << endl;
    return out;
}

int main()
{
    Test obj();
    cout << obj;
    cin >> obj;
    cout << obj;
}