北大C++课后记录：自增、自减运算符重载的小Demo

news2024/10/7 4:25:24

前言

自增、自减运算符有前置（++x）和后置（x++）之分，为了对其进行区分，C++规定：

前置运算符作为一元运算符进行重载：（注意T1对象和T2对象是有差异的）
后置运算符作为二元运算符重载，多写一个没用的参数：

Code

#include <iostream>
#include <algorithm>
#include <cstring>
#include <string.h>
using namespace std;

class CDemo{
    private:
    int n;
    public:
    CDemo(int i = 0): n(i) {}
    ~CDemo(){}
    CDemo(){}
    operator int (){ return n; }        //为能将对象直接传递给构造函数而不调用复制构造函数，省去开销

    //写在class体内时：参数个数 = 运算符目数 - 1
    CDemo& operator ++ ();          //重载前置++
    CDemo operator ++(int);         //重载后置++
    //--写在外面（本质一样）
    friend CDemo& operator -- (CDemo&);
    friend CDemo operator -- (CDemo&, int);
};

CDemo& CDemo :: operator ++ (){
    n += 1;
    return *this;
}

CDemo CDemo :: operator++(int){
    CDemo tmp(*this);
    n += 1;
    return tmp;
}

CDemo& operator -- (CDemo &a){
    a.n -= 1;
    return a;
}

CDemo operator -- (CDemo &a, int){
    CDemo tmp(a);
    a.n -= 1;
    return tmp;
}

int main(){
    CDemo d(5);
    cout << d ++ << ",";
    cout << d << ",";
    cout << ++ d << ",";
    cout << d << endl;
    cout << d -- << ",";
    cout << d << ",";
    cout << -- d << ",";
    cout << d << endl;
    return 0;
}