操作符重載：類成員函數VS友元函數

規則：

作為類成員函數：

1.左操作數必須為該類的對象；

作為友元函數：

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.若想直接通路該類的private和protected成員，非成員操作符函數必須為友元函數。

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>>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: 實作整型數組類的操作符重載：

#include <cassert>

#include <cstdlib>

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();

 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)

 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;

     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

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

istream &operator>>(istream &input, Array &a)

 for(int i=0; i<a.size; i++) input >> a.ptr[i];

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;

 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()

         << integer3 << endl ;

    cout << "Assigning integer2 to integer1:\n" ;

    integer1 = integer2;

    cout << "integer1:\n" << integer1 << 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;