LAB-13 研究以下程式並寫心得, (要自己改一改再測試,) 程式可在這抓到:

  http://www.csie.nctu.edu.tw/~tsaiwn/introcs/LAB-13

Inheritance 繼承就是指示 compiler 把父類別內全部 copy 過來!
注意 constructor 是 在物件(就是變數啦)找好記億位置後立刻去執行的 function.
Destructor 是記憶體要還掉之前的瞬間去執行的 function.
注意   m=258; 會先生出臨時的 _tmp = new B(258); 做 m=_tmp; 再把 _tmp 殺掉!

    1 //ab.cpp -- @CopyLeft by tsaiwn@csie.nctu.edu.tw
    2 // g++  -Wno-deprecated -ab.cpp
    3 //test constructor/destructor and Inheritance
    4 //Note that void test( ) is friend of class B
    5 #include <iostream.h>   // so that can be run under TC++3.0
    6 //using namespace std;
    7 struct A {     // 此例寫 class 也完全相同, why?
    8  protected: 
    9    int data;  
   10  public:
   11    A( ) { cout << "A ";  data = 38;}  // constructor
   12    A(int k) { cout << "Aint "<<k<<" ";  data = k;}
   13   ~A( ) { cout << "A_"<<data<<" dying.."<<endl; }
   14    int getData( ) { return data; }
   15 };
   16 struct B: public A { private:    // 這樣 struct 相當於寫 class
   17  int kkk;
   18  public: B( ) { cout << "B ";  kkk=49;}
   19    B(int x):A(x*10) { kkk=x; cout << "Bint "<<kkk<<" ";  }  // 注意!
   20    B(double x) { kkk=(int)x*100; cout << "BDBL "<<kkk<<" ";  } 
   21   ~B( ) { cout << "B_" << kkk<<" dying .."; }
   22    int getK( ) { return kkk; }
   23    friend void test( );  // claim that void test( ) is my friend
   24 };
   25 void test( ) {
   26   B x(33.555);  
   27   cout << " in test ... "; 
   28   cout << " x.kkk = " << x.kkk << endl;
   29   cout << " x.data = " << x.data << endl;
   30 }
   31 B yy;
   32 extern B m;  // declare m ONLY
   33 int main( ) {  
   34    A xxx(123);  B bb(1357);
   35    cout << "=== ===\n";   
   36    test( );
   37    cout << "\nNow do m=258; \n"; /// will invoke constructor, , destructor
   38    m=258;
   39    //cout << m.data;  // error because main( ) is NOT friend of B
   40    cout << " m.getK()=" << m.getK( ) << endl;
   41    cout << " m.getData()=" << m.getData( ) << endl;
   42    cout << "=== bye ..." << endl; 
   43 }
   44 B m(888);   // define m
   45 /// end of the file

C:\testc>g++ -Wno-deprecated ab.cpp
C:\testc>a.exe
A B Aint 8880 Bint 888 Aint 123 Aint 13570 Bint 1357 === ===
A BDBL 3300  in test ...  x.kkk = 3300
 x.data = 38
B_3300 dying ..A_38 dying..

Now do m=258;
Aint 2580 Bint 258 B_258 dying ..A_2580 dying..    <=====注意這是 m=258; 引起的
 m.getK()=258
 m.getData()=2580
=== bye ...
B_1357 dying ..A_13570 dying..
A_123 dying..
B_258 dying ..A_2580 dying..
B_49 dying ..A_38 dying..

C:\testc>