C++ 逻辑非(!) 运算符重载 - C++ 基础教程

逻辑非(!) 运算符是一元运算符，出现在它们所操作对象的左边 !obj

逻辑非(!) 运算符运算符返回的类型为 bool 类型

当对象为真值时，逻辑非(!) 运算符返回假
当对象为假值时，逻辑非(!) 运算符返回真

/**
 * file: main.cpp
 * author: 简单教程(www.twle.cn)
 *
 * Copyright © 2015-2065 www.twle.cn. All rights reserved.
 */

#include <iostream>

class Rect
{
private:
    int width;             
    int height;          


public:

    Rect(){
        width = 0;
        height = 0;
    }


    Rect( int a, int b ) {
        width = a;
        height = b;
    }

    int area () {

        return width * height;
    }

    // 当 width 或者 height 有一个小于 0 则返回 true

    bool operator!() {
        if ( width <= 0 || height <= 0 ) {
            return true;
        }

        return false;
    }
};


int main()
{
    Rect r1, r2(-1,1), r3(-1,-1), r4(1,1);

    if (!r1)
        std::cout << "r1 is not a rectangle\n";
    else
        std::cout << "r1 is a rectangle\n";

    if (!r2)
        std::cout << "r2 is not a rectangle\n";
    else
        std::cout << "r2 is a rectangle\n";

    if (!r3)
        std::cout << "r3 is not a rectangle\n";
    else
        std::cout << "r3 is a rectangle\n";

    if (!r4)
        std::cout << "r4 is not a rectangle\n";
    else
        std::cout << "r4 is a rectangle\n";


   return 0;
}

使用 g++ main.cpp && ./a.out 命令编译和运行以上范例，输出结果如下：

r1 is not a rectangle
r2 is not a rectangle
r3 is not a rectangle
r4 is a rectangle