操作符重载的概念

复数计算第一种形式(自定义复数类):

#include <stdio.h>

class Complex 
{
    int a;
    int b;
public:
    Complex(int a = 0, int b = 0)
    {
        this->a = a;
        this->b = b;
    }
    
    int getA()
    {
        return a;
    }
    
    int getB()
    {
        return b;
    }
    
    friend Complex Add(const Complex& p1, const Complex& p2);
};

Complex Add(const Complex& p1, const Complex& p2)
{
    Complex ret;
    
    ret.a = p1.a + p2.a;
    ret.b = p1.b + p2.b;
    
    return ret;
}

int main()
{

    Complex c1(1, 2);
    Complex c2(3, 4);
    Complex c3 = Add(c1, c2); // c1 + c2
    
    printf("c3.a = %d, c3.b = %d
", c3.getA(), c3.getB());
    
    return 0;
}

Question:

Add 函数可以解决Complex对象相加的问题;

但是Complex是现实世界的确定存在的复数;

并且复数的地位在数学中的地位与普通的实数地位i相同;

为什么不能+操作符也支持复数相加呢?

操作符重载:

C++中的operator关键字可以定义特殊的函数

operator的本质是通过函数重载操作符;

#include <stdio.h>

class Complex 
{
    int a;
    int b;
public:
    Complex(int a = 0, int b = 0)
    {
        this->a = a;
        this->b = b;
    }
    
    int getA()
    {
        return a;
    }
    
    int getB()
    {
        return b;
    }
    
    friend Complex operator + (const Complex& p1, const Complex& p2);
};

Complex operator + (const Complex& p1, const Complex& p2)
{
    Complex ret;
    
    ret.a = p1.a + p2.a;
    ret.b = p1.b + p2.b;
    
    return ret;
}

int main()
{

    Complex c1(1, 2);
    Complex c2(3, 4);
    Complex c3 = c1 + c2; // operator + (c1, c2)
    
    printf("c3.a = %d, c3.b = %d
", c3.getA(), c3.getB());
    
    return 0;
}

操作符重载的本质就是函数重载.

那还有什么深度挖掘的地方呢?上面的例子我们使用了友元,而友元是我们尽量避免的,那我们可以怎样修改呢?

-可以将操作符重载函数定义为类中的　　成员函数.

　　-比全局操作符重载函数少一个参数(左操作数)

　　-不需要依赖友元就可以完成操作符重载;

　　-编译器优先在成员函数中寻找操作符操作函数;

实例代码分析3:

#include <stdio.h>

class Complex 
{
    int a;
    int b;
public:
    Complex(int a = 0, int b = 0)
    {
        this->a = a;
        this->b = b;
    }
    
    int getA()
    {
        return a;
    }
    
    int getB()
    {
        return b;
    }
    
    Complex operator + (const Complex& p)
    {
        Complex ret;
        printf("Complex operator + (const Complex& p)
");
        ret.a = this->a + p.a;
        ret.b = this->b + p.b;
        
        return ret;
    }
    
    friend Complex operator + (const Complex& p1, const Complex& p2);
};

Complex operator + (const Complex& p1, const Complex& p2)
{
    Complex ret;
    printf("Complex operator + (const Complex& p1, const Complex& p2)
");
    ret.a = p1.a + p2.a;
    ret.b = p1.b + p2.b;
    
    return ret;
}

int main()
{

    Complex c1(1, 2);
    Complex c2(3, 4);
    Complex c3 = c1 + c2; // c1.operator + (c2)
    
    printf("c3.a = %d, c3.b = %d
", c3.getA(), c3.getB());
    
    return 0;
}

小结:

操作符重载是C++的强大特性之一;

操作符重载的本质是通过函数扩展操作符的功能;

operator关键字是实现操作符重载的关键

操作符重载遵循相同的函数重载规则

全局函数和成员函数都可以实现对操作符的重载.