操作符重載：類成員函數VS友元函數

規則：

作爲類成員函數：

1.左操作數必須爲該類的對象；

作爲友元函數：

1.若左操作數不是該類的對象，操作符函數不能作該類的成員函數；

2.若想直接訪問該類的private和protected成員，非成員操作符函數必須爲友元函數。

case1：<<和>>的重載

代碼：

 

ostream &operator<<(ostream &output, const phoneNumber &num)
{
 output <<"("<<num.areaCode<<") "
        <<num.exchange<<"-"<<num.line;
    return output;
}

istream &operator>>(istream &input, phoneNumber &num)
{
 input.ignore();
 input>>setw(4)>>num.areaCode;
 input.ignore(2);
 input>>setw(4)>>num.exchange;
 input.ignore();
 input>>setw(5)>>num.line;
 return input;
}

int main()
{
 phoneNumber phone;
 cout<<"Enter phone number in the form [phone]:\n";
 cin>>phone;
 cout<<"The phone number entered is: "<<phone<<endl;
 return 0;
}

#include <iostream>
using std::cout;
using std::cin;
using std::endl;
using std::ostream;
using std::istream;
#include <iomanip>
using std::setw;
class phoneNumber
{
 friend ostream& operator <<(ostream&, const phoneNumber&);
 friend istream& operator >>(istream&, phoneNumber&);
 private:
 char areaCode[4]; 
 char exchange[4];
 char line[5];
};

 

Enter phone number in the form [phone]:

[phone]

The phone number entered is: [phone]

case2: 實現整型數組類的操作符重載：

代碼：

#include <cassert>
#include <iostream>
#include <cstdlib>
#include <iomanip>
using namespace std ;

class Array
{
 friend ostream &operator<<(ostream&, const Array&);
 friend istream &operator>>(istream&, Array&);
 public:
 Array(int=10);
 Array(const Array&);
 ~Array();
 int getSize() const;
 const Array &operator=(const Array&);
 bool operator==(const Array&) const;
 bool operator!=(const Array &right) const
 { return !(*this==right); }
 int &operator[](int);
 const int &operator[](int) const;
 static int getArrayCount();
 
 private:
 int size;  //array size
 int *ptr;  //ponter to first element
 static int arrayCount;  //# of arrays instantiated
};

int Array::arrayCount= 0; //no object yet

Array::Array(int arraySize)
{
 size = (arraySize > 0 ? arraySize : 10);
 ptr = new int[size];
 assert(ptr!=0); //terminate if memory not allocated
    ++arrayCount;
    for(int i=0; i<size; i++) ptr[i]=0;  
}

Array::Array(const Array &init):size(init.size)
{
 ptr = new int[size];
 assert( ptr !=0);
 ++arrayCount;
 for(int i=0; i<size; i++)
        ptr[i]=init.ptr[i];
}

Array::~Array()
{
 delete []ptr;
 --arrayCount;
}

int Array::getSize() const {return size;}

//const return avoids:(a1=a2)=a3
const Array& Array::operator=(const Array &right)
{
 if(&right != this) //check for self-assignment
 {
  if(size!=right.size)
  {
   delete []ptr;
   size = right.size;
   ptr = new int[size];
   assert(ptr!=0);
  }
  for(int i=0; i<size; i++)
      ptr[i]=right.ptr[i];
 }
 return *this;
}

bool Array::operator==(const Array &right) const
{
 if(size!=right.size) return false;
 
 for(int i=0; i<size; i++)
     if(ptr[i]!=right.ptr[i]) return false;
   
 return true;    
}

int &Array::operator[](int subscript)
{
 assert(0<=subscript && subscript < size);
 return ptr[subscript];
}

const int &Array::operator[](int subscript) const
{
 assert(0<=subscript && subscript < size);
 return ptr[subscript];
}

int Array::getArrayCount() {return arrayCount; }

istream &operator>>(istream &input, Array &a)
{
 for(int i=0; i<a.size; i++) input >> a.ptr[i];
 return input;
}

ostream &operator<<(ostream &output, const Array &a)
{
 for(int i=0; i<a.size; i++)
 {
  output << setw(12)<<a.ptr[i];
        if((i+1)%4==0) output<<endl;
 }
    return output;
}

int main()
{
 cout << "# of arrays instantiated = "
      << Array::getArrayCount()<<endl;
    Array integer1(7), integer2;
    cout << "# of arrays instantiated = "
         << Array::getArrayCount() << endl;
    cout << "Size of array integer1 is "
         << integer1.getSize()
         << "\nArray after initialization:\n"
         << integer1 << endl ;
    cout << "Size of array integer2 is "
         << integer2.getSize()
         << "\nArray after initiazation:\n"
         << integer2 << endl ;
    cout << "Input integers: " << endl;
    cin >> integer1 >> integer2 ;
    cout << "After input, the arrays contain:\n"
         << "integer1:\n" << integer1 << endl
         << "integer2:\n" << integer2 << endl ;
    cout << "Evaluating: integer1!=integer2\n";
    if(integer1!=integer2)
        cout << "They are not equal\n";
    Array integer3(integer1) ;
    cout << "\nSize of array integer3 is "
         << integer3.getSize()
         << "\nArray after initialization:\n"
         << integer3 << endl ;
    cout << "Assigning integer2 to integer1:\n" ;
    integer1 = integer2;
    cout << "integer1:\n" << integer1 << endl
         << "integer2:\n" << integer2 << endl ;
    cout<< "Evaluating: integer1==integer2\n";
    if(integer1==integer2)
       cout << "They are equal" << endl;
       cout << "integer1[5] is " << integer1[5] << endl;
       cout << "Assgning 1000  to integer1[5]\n";
       integer1[5] = 1000 ;
       cout << "integer1:\n" << integer1 << endl;
    return 0;
}