类和对象（13）—— 全局函数与成员函数

1、把全局函数转化成成员函数，通过this指针隐藏左操作数

Test add(Test &t1,Test &t2)    ===>Test add(Test &t2) 

2、把成员函数转换成全局函数，多了一个参数

void printAB() ===>void printAB(Test *pthis)

3、函数返回元素和返回引用

案例一：实现两个test相加

利用全局函数实现两个test相加

#include <iostream>
using namespace std;

class Test
{
public:
    Test(int a, int b)
    {
        this->a = a;
        this->b = b;
    }

    void printT()
    {
        cout << "a:" << this->a << ",b:" << this->b << endl;
    }

    int getA()
    {
        return this->a;
    }

    int getB()
    {
        return this->b;
    }
private:
    int a;
    int b;
};

//在全局提供一个两个test相加的函数
Test TestAdd(Test &t1, Test &t2)
{
    Test temp(t1.getA() + t2.getA(), t1.getB() + t2.getB());
    return temp;
}

int main(void)
{
    Test t1(10, 20);
    Test t2(100, 200);

    Test t3 = TestAdd(t1, t2);
    t3.printT();//a:110,b:220

    return 0;
}

利用成员函数实现两个test相加：

#include <iostream>
using namespace std;

class Test
{
public:
    Test(int a, int b)
    {
        this->a = a;
        this->b = b;
    }

    void printT()
    {
        cout << "a:" << this->a << ",b:" << this->b << endl;
    }

    int getA()
    {
        return this->a;
    }

    int getB()
    {
        return this->b;
    }

    //用成员方法实现两个test相加，函数返回元素
    Test TestAdd(Test &another)
    {
        Test temp(this->a + another.getA(), this->b + another.getB());
        return temp;
    }
private:
    int a;
    int b;
};

int main(void)
{
    Test t1(10, 20);
    Test t2(100, 200);

    Test t3 = t1.TestAdd(t2);
    t3.printT();//a:110,b:220

    return 0;
}

案例二：实现test的+=操作

#include <iostream>
using namespace std;

class Test
{
public:
    Test(int a, int b)
    {
        this->a = a;
        this->b = b;
    }

    void printT()
    {
        cout << "a:" << this->a << ",b:" << this->b << endl;
    }

    int getA()
    {
        return this->a;
    }

    int getB()
    {
        return this->b;
    }

　　//+=方法
    void TestAddEqual(Test &another)
    {
        this->a += another.a;
        this->b += another.b;
    }

private:
    int a;
    int b;
};

int main(void)
{
    Test t1(10, 20);
    Test t2(100, 200);

    t1.TestAddEqual(t2);
    t1.printT();

    return 0;
}

案例三：连加等

#include <iostream>
using namespace std;

class Test
{
public:
    Test(int a, int b)
    {
        this->a = a;
        this->b = b;
    }

    void printT()
    {
        cout << "a:" << this->a << ",b:" << this->b << endl;
    }

    int getA()
    {
        return this->a;
    }

    int getB()
    {
        return this->b;
    }

    //如果想对一个对象连续调用成员方法，每次都会改变对象本身，成员方法需要返回引用
    Test& TestAddEqual(Test &another)//函数返回引用
    {
        this->a += another.a;
        this->b += another.b;

        return *this;//如果想返回一个对象本身，在成员方法中，用*this返回
    }
private:
    int a;
    int b;
};

int main(void)
{
    Test t1(10, 20);
    Test t2(100, 200);

    t1.TestAddEqual(t2).TestAddEqual(t2);
    t1.printT();//a:210,b:420

    return 0;
}