运算符重载

1.+重载

#include<iostream>  using namespace std;  class Brass  {  int length;  public:  Brass(int _length=0):length(_length){}  Brass(Brass& brass){length=brass.length;}Brass operator+(Brass& brass)//基类普通重载----#1  {  return Brass(length+brass.length);  }  //改变length的值，即length+n  Brass operator+(int n)//基类普通重载-----#2   {  return Brass(length+n);  }  friend Brass operator+(int n,Brass& brass)//基类友元重载------#3  {  return Brass(n+brass.length);  }  virtual void show(){cout<<length;}};  class BrassPlus:public Brass{int width;public:BrassPlus(int _length=0,int _width=0):Brass(_length),width(_width){}BrassPlus(Brass& brass,int _width=0):Brass(brass),width(_width){}friend BrassPlus operator+(BrassPlus& brassplus,int n)//派生类友元重载{Brass brass=(Brass&)brassplus+n;//强制转换去掉后会进入函数自己的死循环//这里的强制转换是引用，而不是(Brass)brassplus，//这样可以在函数无意修改值得话，brassplus的值也会随之改变return BrassPlus(brass,n+brassplus.width);}virtual void show(){Brass::show();cout<<" "<<width<<endl;}};int main()  {  //测试基类Brass one;  Brass two;  Brass add;  int n=2;  add=one+two;//use Brass operator+(Brass& brass)  add=one+n;//use Brass operator+(int n)如果#3的代码没写，那么add=n+one；这样的写法就是错的  add=n+one;//use friend Brass operator+(int n,Brass& brass)  //如果要为类重载运算符，并将非类的项作为第一个操作数，则可以用友元函数来反转操作数的顺序。  //就像#2和#3的搭配  //测试派生类BrassPlus bone;BrassPlus btwo=bone+2;btwo.show();//--->2 2return 0;  }  

2.<<重载

<<的重载只能用友元函数。为什么呢？因为假如是这样的语句，cout<<brass;

第一个操作数是cout,即ostream类对象

如果使用普通的成员函数来重载，那么第一个操作数就一定是Brass类对象。

#include<iostream>  using namespace std;  class Brass  {  int length;  public:  Brass(int _length=0):length(_length){}  Brass(Brass& brass){length=brass.length;}friend ostream& operator<<(ostream& os,Brass& brass)//基类友元重载{os<<brass.length;return os;}};  class BrassPlus:public Brass{int width;public:BrassPlus(int _length=0,int _width=0):Brass(_length),width(_width){}BrassPlus(Brass& brass,int _width=0):Brass(brass),width(_width){}friend ostream& operator<<(ostream& os,BrassPlus& brassplus)//派生类友元重载{os<<(Brass&)brassplus<<" ";os<<brassplus.width<<endl;return os;}};int main()  {  Brass one(21);cout<<one<<endl;//-->21BrassPlus bone(21,2121);cout<<bone<<endl;//-->21 2121/*由于友元函数并非类成员，因此不能继承。然而您可能希望派生类的友元函数可以使用基类的友元函数。为此，可以通过强制类型转换实现。*/return 0;  }  

3.负号-重载，减号的重载和加号的重载一样，不作讲述

#include<iostream>using namespace std;class Brass{int length;public:Brass(int _length=0):length(_length){}Brass operator-();//符号重载friend ostream& operator<<(ostream& os, Brass& brass);};Brass Brass::operator-(){return Brass(-length);}ostream& operator<<(ostream& os, Brass& brass){os << brass.length << endl;return os;}int main(){Brass one(5);one = -one;cout << one;//---->-5return 0;}

4.[ ]重载

#define _CRT_SECURE_NO_DEPRECATE//#define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES 1#include<iostream> #include<string>using namespace std;class String{char *str;int length;public:String(char *_str = "null", int _length = 4):length(_length){str = new char[5];strcpy(str, _str);}char &operator[](int i){return str[i];}};int main(){String one("ZhangSan", 8);cout << one[0] << endl;//Zcout << one[2] << endl;//areturn 0;}

5.=重载（主要是深度复制方面）

#define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES 1  #include<iostream>#include<string.h>using namespace std;class Base{char *ch;public:Base(char *_ch = "null"){ch = new char[strlen(_ch) + 1];strcpy(ch, _ch);}virtual ~Base(){delete []ch;}Base & operator=(const Base & base){if (this == &base)return *this;delete[]ch;ch = new char[strlen(base.ch) + 1];strcpy(ch, base.ch);return *this;}};class BasePlus :public Base{char *s;public:BasePlus(char *_ch = "null", char *_s = "null"):Base(_ch){s = new char[strlen(_s) + 1];strcpy(s, _s);}virtual ~BasePlus(){delete []s;}BasePlus & operator=(const BasePlus& basePlus){if (this == &basePlus)return *this;Base::operator=(basePlus);delete[]s;s = new char[strlen(basePlus.s) + 1];strcpy(s, basePlus.s);return *this;}};int main(){return 0;}

6.++重载

#define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES 1  #include<iostream>using namespace std;class Base{int length;public:Base(int _length=0):length(_length){}Base& operator++()//前自加{length += 1;//自加多少由自己决定,由此可见C++重载的大大优势return *this;}Base operator++(int)//后自加{Base temp(*this);++(*this);return temp;}friend ostream& operator<<( ostream &os, const Base &base){os << base.length << endl;return os;}};int main(){Base one;cout << one;//0cout << one++;//0cout << one;//1return 0;}

7.>>和getline重载

#define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES 1  #include<iostream>#include<string>using namespace std;class Student{string name;public:Student(string _name = "null") :name(_name) {}friend istream & operator>>(istream & is, Student & student){is >> student.name;return is;}friend istream & getline(istream & is, Student & student){getline(is, student.name);return is;}friend ostream & operator<<(ostream & os, Student & student){os << student.name << endl;return os;}};int main(){Student one;Student two;cin >> one;//lisancout << one;//lisanchar x = getchar();//吃掉换行符，不然下面的语句没有作用getline(cin, two);//li sancout << two;//li sanreturn 0;}