三、几个典型运算符重载

1.++与–

①成员函数

#include<iostream>
using namespace std;
class  Increase
{ public :Increase ( ) { value=0; }void  display( )  const { cout<<value<<'\n'; } ;Increase  operator ++ ( ) ; 	     // 前置Increase  operator ++ ( int ) ;    // 后置**（返回的是拷贝值而不是本身）private:   unsigned  value ;
};
Increase  Increase :: operator ++ ( ) //前置	{ value ++ ;   return *this ; }	
Increase  Increase :: operator ++ ( int )//后置	{ Increase  temp;   temp.value = value ++ ;   return  temp; }
int main( ){ Increase   a ,  b , n ;    int  i ;for ( i = 0 ; i < 10 ; i ++ )  a = n ++ ;cout <<"n= " ;  n.display( ) ;   cout <<"a= " ;   a.display( ) ;for ( i = 0 ; i < 10 ; i ++ )  b = ++ n ;cout << "n= " ;   n.display( ) ;   cout << "b= " ;   b.display( ) ;}

②友元函数

#include<iosstream>
using namespace std;
class Increase
{public:Increase () {value=0;}void display() const {cout<<value<<'\n'};friend Increase operator ++();//前置friend Increase operator ++(Increase &,int);//后置private: unsigned value;
};
Increase Increase:: operator ++(Increase &)
{I.value++; return I;}
Increase Increase:: operator ++(Increase &I,int)
{Increase  temp(a);   I.value ++ ;   return  temp;}
int main( ){ Increase   a ,  b , n ;    int  i ;for ( i = 0 ; i < 10 ; i ++ )  a = n ++ ;cout <<"n= " ;  n.display( ) ;   cout <<"a= " ;   a.display( ) ;for ( i = 0 ; i < 10 ; i ++ )  b = ++ n ;cout << "n= " ;   n.display( ) ;   cout << "b= " ;   b.display( ) ;}

2.重载赋值运算符

①条件

• 赋值运算符重载用于对象数据的复制
• operator= 必须重载为成员函数
• 重载函数原型为：类名 & 类名 :: operator= ( 类名 ) ;

②代码

#include<iostream>
#include<cstring>
using namespace std;
class  Name
{ public :Name ( char  *pN ) ;Name( const Name & ) ;		    //复制构造函数 Name& operator=( const Name& ) ;	    // 重载赋值运算符~ Name() ;protected : char  *pName ;int size ;
} ;int main()
{ Name Obj1( "ZhangSan" ) ;Name Obj2 = Obj1 ;		// 调用复制构造函数 Name Obj3( "NoName" ) ;Obj3 = Obj2 = Obj1 ;		// 调用重载赋值运算符函数 
}
Name::Name ( char  *pN ){ cout <<" Constructing " << pN << endl ;pName = new char[ strlen( pN ) + 1 ] ;if( pName != 0 ) strcpy( pName,pN ) ;size = strlen( pN ) ;}
Name::Name( const Name & Obj )	 //复制构造函数
{ cout << " Copying " << Obj.pName << " into its own block\n";pName = new char[strlen( Obj.pName ) + 1 ] ;if ( pName != 0 ) strcpy( pName, Obj.pName ) ;size = Obj.size;
}
Name & Name::operator= ( const Name & Obj )	 // 重载赋值运算符
{ delete  []pName ;//释放内存pName = new char[ strlen( Obj.pName ) + 1 ] ;if ( pName != 0 ) strcpy( pName , Obj.pName ) ;size = Obj.size ;return *this ;
}
Name::~ Name()
{ cout << " Destructing " << pName << endl ;delete  []pName ;size = 0;
}

3.重载运算符[]和()

①前提

• 运算符 [] 和 () 是二元运算符
• [] 和 () 只能用成员函数重载，不能用友元函数重载

②重载下标运算符 []

[] 运算符用于访问数据对象的元素

重载格式 类型 类 :: operator[] ( 类型 ) ；

#include<iostream>
using namespace std;
class  vector
{ public :vector ( int  n )  {  v = new  int [ n ] ; size = n ; }~ vector ( )  { delete [ ] v ; size = 0 ; }int & operator [ ] ( int  i )  {  return  v [ i ] ; }//返回为引用，以便修改private :       int * v ;       int size ;
};
int main ( )
{  vector  a ( 5 ) ;a [ 2 ] = 12 ;	  cout << a [ 2 ] << endl ;
}

③重载函数调用符 ()

() 运算符用于函数调用

重载格式 类型 类 :: operator() ( 参数表 ) ；

#include <iostream>
using namespace std ;
class  F{ public :  double  operator ( )  ( double x ,  double  y ) ;} ;
double  F :: operator ( )  ( double  x ,  double  y ){ return   x * x + y * y ; }
int main ( )			
{ F  f  ;cout << f ( 5.2 , 2.5 ) << endl ;
}

④重载流插入和流提取运算符

a.前提

• istream 和 ostream 是 C++ 的预定义流类
• cin 是 istream 的对象，cout 是 ostream 的对象
• 运算符 << 由ostream 重载为插入操作，用于输出基本类型数据
• 运算符 >> 由 istream 重载为提取操作，用于输入基本类型数据
• 用友元函数重载 << 和 >> ，输出和输入用户自定义的数据类型

include<iostream>
#include<cstdlib>
using namespace std;
class vector
{ public :vector( int size =1 ) ;       ~vector() ;int & operator[] ( int i ) ;friend ostream & operator << ( ostream & output , vector & ) ;friend istream & operator >> ( istream & input, vector & ) ;private :  int * v ;     int len ;
};
int main()
{ int k ;cout << "Input the length of vector A :\n" ;     cin >> k ;vector A( k ) ;cout << "Input the elements of vector A :\n" ;     cin >> A ;cout << "Output the elements of vector A :\n" ;cout << A ;
}
vector::vector( int size ) 
{ if (size <= 0 || size > 100 ){ cout << "The size of " << size << " is null !\n" ; exit( 0 ) ;  }v = new int[ size ] ;  len = size ;
}
vector :: ~vector() { delete[] v ;  len = 0 ; }
int & vector :: operator [] ( int i ) 		
{ if( i >=0 && i < len )  return v[ i ] ;cout << "The subscript " << i << " is outside !\n" ;  exit( 0 ) ;
}
ostream & operator << ( ostream & output, vector & ary )
{ for(int i = 0 ; i < ary.len ; i ++ )  output << ary[ i ] << "  " ;output << endl ;return output ;
}
istream & operator >> ( istream & input, vector & ary )	
{ for( int i = 0 ; i < ary.len ; i ++ )  input >> ary[ i ] ;return  input ;
}