运算符重载的本质是一个函数

#include 
      
       using namespace std;class A {private:    int m_a;    int m_b;    friend A operator+(A &a1, A &a2);//友元函数訪问私有属性。实现二元运算符重载    friend A operator++(A &a); //友元函数訪问私有属性。实现一元运算符重载（前置）    /*后置为避免与前置函数定义同样，使用占位符int。告诉编译器是后置运算符重载*/    friend A operator++(A &a, int); //友元函数訪问私有属性。实现一元运算符重载（后置）    friend class B; //友元类，訪问私有属性。
      

若B类是A类的友员类，则B类的全部成员函数都是A类的友员函数

public: A(int a){ this->m_a = a; } A(int a, int b) { m_a = a; m_b = b; } void show() { cout << m_a << endl; } }; class B { private: A *pObjA = new A(21); public: void showA() { cout << pObjA->m_a << endl; } }; A operator+(A &a1, A &a2) { A tmp(a1.m_a + a2.m_a, a1.m_b + a2.m_b); return tmp; } A operator++(A &a) { //前置++ a.m_a++; a.m_b++; return a; } A operator++(A &a, int) { //后置++ A tmp = a; a.m_a++; a.m_b++; return tmp; } int main() { A a1(1, 9); A a2(3, 4); A a3 = a1 + a2; a3.show(); ++a3; a3.show(); a3++; a3.show(); return 0; }

class Complex{public:    int a;    int b;    friend Complex operator+(Complex &c1, Complex &c2);public:    Complex(int a=0, int b=0)    {        this->a = a;        this->b = b;    }public:    void printCom()    {        cout<<<" + "<<<"i "<

为vector类重载流插入运算符和提取运算符

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 ;};vector::vector( int size ) {     if (size <= 0 || size > 100 )    {         cout << "The size of " << size << " is null !\n" ; abort() ;      }    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" ;  abort() ;}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 ;}void 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 ;    system("pause");}