操作符重载的概念

我们先来看下面这个例子是否能编译通过
实现复数的相加

#include <stdio.h>
class Complex
{
  public:
  int a;
  int b;
};
int main()
{
   Complex c1 = {1,2};
   Complex c2 = {3,4};
   Complex c3 = c1 + c2;
   return 0;
}

结果:

sice@sice:~$ g++ c.cpp 
c.cpp: 在函数‘int main()’中:
c.cpp:12:22: 错误： ‘operator+’在‘c1 + c2’中没有匹配

显然C++不支持这样对象直接相加
改进(1):

#include <stdio.h>
class Complex
{
  private:
  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(Complex &p1,Complex &p2);
};
Complex Add(Complex &p1,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\n", c3.getA(), c3.getB());
    
    return 0;
}

结果:

sice@sice:~$ ./a.out 
c3.a = 4, c3.b = 6

缺点:但是还是感觉过于复杂,希望能直接使用+进行操作,这次改进不算成功,
升级:所以这里就引入了操作符重载

操作符重载
C++中的重载能够扩展操作符的功能
操作符的重载以函数的方式进行
本质:
用特殊形式的函数扩展操作符的功能

改进(2):

#include <stdio.h>
class Complex
{
  private:
  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 +(Complex &p1,Complex &p2);
};
Complex operator +(Complex &p1,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; // c1 + c2
    
    printf("c3.a = %d, c3.b = %d\n", c3.getA(), c3.getB());
    
    return 0;
}

结果:
输出一致,当执行到c1+c2的时候,编译器就去找有没有+操作符的重载呢,发现找到该函数体,让+的左操作数和右操作数与函数参数列表比较是否匹配,匹配的话执行函数
缺点:
使用了友元,破坏了封装性
升级:
可以将操作符重载函数定义为类的成员函数,隐藏的this指针作为左操作数,对于操作符重载函数而言,成员函数优先级大于全局函数

改进(3):

#include <stdio.h>
class Complex
{
  private:
  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 +(Complex &p2)
 {
    Complex ret;    
    ret.a = this->a + p2.a;
    ret.b = this->b + p2.b; 
    return ret;
 }
};
/*Complex operator +(Complex &p1,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; // c1 + c2
    
    printf("c3.a = %d, c3.b = %d\n", c3.getA(), c3.getB());
    
    return 0;
}

最后我们来实现一个完整的复数类

来源：CSDN

作者：勇士后卫头盔哥

链接：https://blog.csdn.net/qq_41936794/article/details/104654574