tsaiwn@magpie handout> cat -n polymo.cpp
     1  // polymo.cpp -- CopyWrong by tsaiwn@csie.nctu.edu.tw
     2  #include <iostream.h>
     3  class Shape{
     4     public:
     5       virtual   // 把這列去掉再 run 看看
     6         void draw(){ cout << "drawing\n"; }
     7  };
     8  class Line: public Shape{
     9     public:
    10        void draw(){ cout << "draw a line\n"; }
    11  };
    12  class Circle: public Shape{
    13     public:
    14        void draw(){ cout << "here is a circle\n"; }
    15  };
    16  int main(){
    17     Circle * ppp;
    18     Shape * fig[5];
    19    // ppp = new Shape();   // error
    20     ppp = (Circle *)new Shape();
    21     ppp -> draw();
    22     ppp = (Circle *)new Line();
    23     ppp -> draw();
    24     ppp = new Circle();
    25     ppp -> draw();
    26     cout << "======" << endl;
    27     fig[0] = new Line();
    28     fig[1] = new Circle();
    29     fig[2] = new Circle();
    30     fig[3] = new Line();
    31     fig[4] = new Circle();
    32     for(int k=0; k<5; k++){
    33        fig[k] -> draw();
    34     }
    35  }
tsaiwn@magpie handout> g++ polymo.cpp
tsaiwn@magpie handout> ./a.out
drawing
draw a line
here is a circle
======
draw a line
here is a circle
here is a circle
draw a line
here is a circle
tsaiwn@magpie handout> 
tsaiwn@magpie handout> g++ -v
Using builtin specs.
gcc version 2.95.4 20020320 [FreeBSD]

tsaiwn@magpie handout> g++ not-poly.cpp    <== 刪掉 line 5  virtual  後
tsaiwn@magpie handout> ./a.out
here is a circle
here is a circle
here is a circle
======
drawing
drawing
drawing
drawing
drawing
tsaiwn@magpie handout> exit
exit

Script done on Wed Feb 25 23:30:37 2004