Re: static array declaration in flyweight pattern

I'm concerned about this code which I saw from sourcemaking.com pasted
below. In particular, I question the line -- Icon
*FlyweightFactory::_icons[]; I have marked this line out below by =

************* so that those interested can easily find it in
context. My question is quite simple, and only a tiny fraction of the
pasted code is probably relevant. (But I provided full context just
in case.)

The line Icon *FlyweightFactory::_icons[]; seems a strange definition
of an array. In the class Icon, this array is declared as having
dimension 5 but the definition doesn't specify the size.
The definition of the array also appears to be uninitialized. In
particular, I would be interested to know if the static array
declaration ensures that all the int-pointer members of the array are
null pointers. They are either null pointers or uninitialized
pointers but which?

I would probably have written Icon *FlyweightFactory::_icons[] = {0,
0, 0, 0, 0};

but it's possible that the code does this anyway. Do the int-pointers
initialize to 0 anyway even if this is not made explicit as I did?

Thanks very much for your help.

Paul Epstein

#include <iostream.h>
#include <string.h>

class Icon
{
  public:
    Icon(char *fileName)
    {
        strcpy(_name, fileName);
        if (!strcmp(fileName, "go"))
        {
            _width = 20;
            _height = 20;
        }
        if (!strcmp(fileName, "stop"))
        {
            _width = 40;
            _height = 40;
        }
        if (!strcmp(fileName, "select"))
        {
            _width = 60;
            _height = 60;
        }
        if (!strcmp(fileName, "undo"))
        {
            _width = 30;
            _height = 30;
        }
    }
    const char *getName()
    {
        return _name;
    }
    draw(int x, int y)
    {
        cout << " drawing " << _name << ": upper left (" << x=

<< y <<
          ") - lower right (" << x + _width << "," << y + _heig=

")" <<
          endl;
    }
  private:
    char _name[20];
    int _width;
    int _height;

};

class FlyweightFactory
{
  public:
    static Icon *getIcon(char *name)
    {
        for (int i = 0; i < _numIcons; i++)
          if (!strcmp(name, _icons[i]->getName()))
            return _icons[i];
        _icons[_numIcons] = new Icon(name);
        return _icons[_numIcons++];
    }
    static void reportTheIcons()
    {
        cout << "Active Flyweights: ";
        for (int i = 0; i < _numIcons; i++)
          cout << _icons[i]->getName() << " ";
        cout << endl;
    }
  private:
    enum
    {
        MAX_ICONS = 5
    };
    static int _numIcons;
    static Icon *_icons[MAX_ICONS];

};

int FlyweightFactory::_numIcons = 0;
Icon *FlyweightFactory::_icons[]; //
*************************************************************************=

class DialogBox
{
  public:
    DialogBox(int x, int y, int incr): _iconsOriginX(x), _iconsOrigin=

(y),
      _iconsXIncrement(incr){}
    virtual void draw() = 0;
  protected:
    Icon *_icons[3];
    int _iconsOriginX;
    int _iconsOriginY;
    int _iconsXIncrement;

};

class FileSelection: public DialogBox
{
  public:
    FileSelection(Icon *first, Icon *second, Icon *third): DialogBox
(100, 100,
      100)
    {
        _icons[0] = first;
        _icons[1] = second;
        _icons[2] = third;
    }
    void draw()
    {
        cout << "drawing FileSelection:" << endl;
        for (int i = 0; i < 3; i++)
          _icons[i]->draw(_iconsOriginX + (i *_iconsXIncrement)=

_iconsOriginY);
    }

};

class CommitTransaction: public DialogBox
{
  public:
    CommitTransaction(Icon *first, Icon *second, Icon *third):
DialogBox(150,
      150, 150)
    {
        _icons[0] = first;
        _icons[1] = second;
        _icons[2] = third;
    }
    void draw()
    {
        cout << "drawing CommitTransaction:" << endl;
        for (int i = 0; i < 3; i++)
          _icons[i]->draw(_iconsOriginX + (i *_iconsXIncrement)=

_iconsOriginY);
    }

};

int main()
{
  DialogBox *dialogs[2];
  dialogs[0] = new FileSelection(FlyweightFactory::getIcon("go"),
    FlyweightFactory::getIcon("stop"), FlyweightFactory::getIcon
("select"));
  dialogs[1] = new CommitTransaction(FlyweightFactory::getIcon
("select"),
    FlyweightFactory::getIcon("stop"), FlyweightFactory::getIcon
("undo"));

  for (int i = 0; i < 2; i++)
    dialogs[i]->draw();

  FlyweightFactory::reportTheIcons();

}