运算符重载（前置/后置++、前置/后置--和+=/-=/-/+/=)

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特殊运算符
=, [], () 和 -> 操作符只能通过成员函数进行重载
<< 和 >> 操作符最好通过友元函数进行重载
不要重载 && 和 || 操作符，因为无法实现短路规则
这里写图片描述

#include <stdlib.h>#include <iostream>using namespace std;class Student{public:    Student(const char *name,int age)    {        /*若name为NULL字符串，则申请一个char内存空间，直接赋予0即可*/        if(NULL == name)        {            m_Pname = new char[1];            m_Pname[0] = '\0';        }        /*若name不为NULL，则申请一段内存空间来存储m_Pname*/        m_Pname = new char[strlen(m_Pname) + 1];        strcpy(this->m_Pname,name);        this->m_age = age;    }    Student(){}    ~Student()    {        if (this->m_Pname != NULL)        {            delete[] this->m_Pname;            this->m_Pname = NULL;        }    }private:    char *m_Pname;    int m_age;};void test(){    Student s1("lixiaogang",24);    Student s2;    /*赋值操作*/    s2 = s1;}int main(){    test();    system("pause");    return 0;}

运行代码后会出现严重bug 导致程序直接死掉；原因是因为涉及到了动态内存空间的申请，因此利用C++提供的简单赋值函数不能解决问题，的自己定义一个赋值函数；

I. 重载赋值运算符

#include <stdlib.h>#include <iostream>using namespace std;class Student{public:    Student(const char *name,int age)    {        /*若name为NULL字符串，则申请一个char内存空间，直接赋予0即可*/        if(NULL == name)        {            m_Pname = new char[1];            m_Pname[0] = '\0';        }        /*若name不为NULL，则申请一段内存空间来存储m_Pname*/        m_Pname = new char[strlen(name) + 1];        strcpy(this->m_Pname,name);        this->m_age = age;    }    Student(const Student& s);    Student(){}    ~Student()    {        if (this->m_Pname != NULL)        {            delete[] this->m_Pname;            this->m_Pname = NULL;        }    }public:    void display()    {        cout<<"m_Pname = "<<this->m_Pname<<endl;        cout<<"m_age = "<<this->m_age <<endl;    }    Student& operator=(const Student& s);private:    char *m_Pname;    int m_age;};Student::Student(const Student& s){    m_Pname = new char[strlen(s.m_Pname) + 1];    strcpy(this->m_Pname,s.m_Pname);    this->m_age = s.m_age;}/**** 重载赋值运算符 ****/Student& Student::operator=(const Student& s){    /*1步：若原来的对象有值不为NULL，则先将其内存空间释放掉*/    if (this->m_Pname != NULL)    {        delete[] this->m_Pname;        this->m_Pname = NULL;    }    /*2步：为对象重新分配s.m_Pname大小的内存空间*/    /*内存大小为strlen(s.n_Pname)+1,要为字符串结束符分配一字节的空间*/    this->m_Pname = new char[strlen(s.m_Pname) + 1];    /*3步：为对象赋值*/    strcpy(this->m_Pname,s.m_Pname);    this->m_age = s.m_age;    return *this;}void test(){    Student s1("lixiaogang",24);    Student s2("hello",22);    /*赋值操作*/    s2 = s1;    s1.display();    puts("------------");    s2.display();}int main(){    test();    system("pause");    return 0;}

打印结果：

m_Pname = lixiaogangm_age = 24---------------m_Pname = lixiaogangm_age = 24

注意：下列代码中若Student s2("hello",22); 改为Student s2;然后再执行：s2 = s1;会出现程序死掉的现象；原因在于我的默认构造函数中为空，没有做任何的操作，因此执行赋值操作的时候相当于操作一个野指针，这时去释放一个野指针就会出现错误了。

Student s1("lixiaogang",24);    Student s2("hello",22);    /*赋值操作*/    s2 = s1;

解决方案是修改默认的构造函数：

Student(){this->m_Pname = NULL;this->m_age = 0;}让其不再执行一个随机的内存空间，这样就不会出现野指针操作的情况。

void test(){    Student s1("lixiaogang",24);    Student s2;    /*赋值操作*/    s2 = s1;   //ok 不会出现问题    s1.display();    puts("------------");    s2.display();}

II.重载前置/后置++、前置/后置 - -

示例代码：

#include <stdlib.h>#include <iostream>using namespace std;class Student{public:    //重载运算符<<    friend ostream& operator<<(ostream& os,const Student& s);    //重载运算符>>    friend istream& operator>>(istream& in,Student& s);    //重载运算符++(前置)    Student& operator++();    //重载运算符++（后置）    Student operator++(int);    //重载运算符--（前置）    Student& operator--();    //重载运算符--（后置）    Student operator--(int);    //重载运算符+=    Student& operator+=(const Student& s);    //重载运算符-=    Student& operator-=(const Student& s);    //重载运算符+    Student operator+(const Student& s);    //重载运算符-    Student operator-(const Student& s);    //普通成员函数    void display();public:    //构造函数；初始化列表    Student(int age,int salary):m_age(10),m_salary(salary){}    //无参数构造函数    Student(){m_age = 0;m_salary = 1000;}    //析构函数    ~Student(){}private:    int m_age;    int m_salary;}; ostream& operator<<(ostream& os,const Student& s) {     os<<"s.m_age = "<<s.m_age<<endl;     os<<"s.m_salary = "<<s.m_salary<<endl;     return os; } istream& operator>>(istream& in,Student& s) {     in>>s.m_age>>s.m_salary;     return in; }Student& Student:: operator++(){    ++this->m_age;    ++this->m_salary;    return *this;}//**************************后置++为了区分前置++与后置++的区别，c++规定了后置++/——操作时，再operator++/operator--后面的括号里加上一个int占位符；用以区别前置与后置的差异；如：operator++（int）;operator--(int)//**************************Student  Student::operator++(int){    /*     Student s_temp;     s_temp.m_age = this->m_age;     s_temp.m_salary = this->m_salary;     m_age++;     m_salary++;     return s_temp;*/    //和上面代码等价    Student s_temp(*this);    this->m_age++;    this->m_salary++;    return s_temp;}Student&  Student::operator--(){    --this->m_age;    --this->m_salary;    return *this;}Student  Student::operator--(int){    Student s_temp;    s_temp.m_age = m_age;    s_temp.m_salary = m_salary;    m_age--;    m_salary--;    return s_temp;    //和下面代码等价    /*Student s_temp(*this);    m_age--;    m_salary--;    return s_temp;*/}Student&  Student::operator+=(const Student& s){    this->m_age+=s.m_age;    this->m_salary+=s.m_salary;    return *this;}Student&  Student::operator-=(const Student& s){    this->m_age -= s.m_age;    this->m_salary -= s.m_salary;    return *this;}Student Student::operator+(const Student& s){    this->m_age += s.m_age;    this->m_salary += s.m_salary;    return *this;}Student Student::operator-(const Student& s){    /*Student s_temp = *this;    s_temp.m_age = this->m_age - s.m_age;    s_temp.m_salary = this->m_salary - s.m_salary;    return s_temp;*/    //等价    this->m_age -= s.m_age;    this->m_salary -= s.m_salary;    return *this;}void Student::display(){    cout<<"m_age = "<<m_age<<endl;    cout<<"m_salary = "<<m_salary<<endl;}void test(){    Student s1(22,1000);    Student s2(11,2000);    s2.display();    puts("-----------");    ++s2;    s2.display();    puts("-----------");    cout<<s2++<<endl;    puts("-----------");}int main(){    test();    system("pause");    return 0;}

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