10:37am ccbsd3:friend/> cat -n fra.cpp
     1  //fra.cpp  -- by tsaiwn@csie.nctu.edu.tw
     2  #include <iostream>
     3  using namespace std;
     4  class Student {
     5     int kk;    // 自動設為 private
     6   public:
     7     Student( ) { kk=0; cout << "Bin\n"; }
     8     ~Student( ) { cout << "Hey.. "<<kk<< "即將離去\n"; }
     9  };
    10  int main( ) {
    11     Student x;
    12     cout << "value in x = " << x.kk << endl;
    13  }
10:37am ccbsd3:friend/> g++ fra.cpp
fra.cpp: In function `int main()':
fra.cpp:5: error: `int Student::kk' is private
fra.cpp:12: error: within this context
10:37am ccbsd3:friend/>





10:38am ccbsd3:friend/> cat -n frb.cpp
     1  //frb.cpp  -- by tsaiwn@csie.nctu.edu.tw
     2  #include <iostream>
     3  using namespace std;
     4  class Student {
     5     int kk;
     6   public:
     7     Student( ) { kk=0; cout << "Bin\n"; }
     8     Student(int x) { cout << "Bon "; kk=x;}
     9     ~Student( ) { cout << "Hey.. "<<kk<< "即將離去\n"; }
    10     friend int main( );  // int main( ) is my friend :-)
    11  }; // friend is the ONLY one who can touch your private.
    12  void test( ) {
    13     Student a(38), b(49);
    14      cout << "本山人到此一遊" << endl;  // endl 與 "\n" 同
    15  }
    16  Student mm;
    17  int main( ) {
    18     cout << "======開始囉======" << endl;
    19     Student x(88);
    20     Student *p;
    21     cout << "value in x = " << x.kk << endl;
    22     p = new Student(258);
    23     cout << "now calling test...\n";
    24     test( );
    25     cout << "Bye bye!" << endl;
    26     return 0;
    27  }
10:38am ccbsd3:friend/> g++ frb.cpp
10:38am ccbsd3:friend/> ./a.out
Bin
======開始囉======
Bon value in x = 88
Bon now calling test...
Bon Bon 本山人到此一遊
Hey.. 49即將離去
Hey.. 38即將離去
Bye bye!
Hey.. 88即將離去
Hey.. 0即將離去
10:38am ccbsd3:friend/>