How to create an array of buttons on Borland C++ Builder and work with it?

Question

Specific question

How to create an array of buttons on Borland C++ Builder and work with it?

I'm using Borland C++ Builder 6 and Borland Developer Studio 2006 (Turbo C++ 2006).

Purpose

To work with a lot of buttons on a form just using a for loop with an index, for example, changing their caption, size and position.

I know if I have a button called Button1 and inside a click event of this button if I create another button (through TButton *Button2 = new TButton(Form1)), I can assign Button1 to Button2 (Button2 = Button1) and them I can simply modify caption of Button1 with Button2->Caption. So I would like to extend it assigning pointers of real components to elements of an array to them work with all of them with a for loop.

Well, if someone found an way to add all buttons as an array on a form, it's better :)

Tries

Following tests were made putting respective code on TForm1::Button1Click(), an event of a button on a form:

• Test 1

  • Description: Creating an array directly

  • Code:

    TButton Buttons[3];
    

  • Result: Compile error:

    > [C++ Error] Unit1.cpp(23): E2248 Cannot find default constructor
    > to initialize array element of type 'TButton'
    

  • Comments:
    • I tested some variants of this test (e.g. TButton Buttons = new TButton[3], working with calloc function and others), but all of them points to the issue that TButton does not have a constructor without arguments, i.e., TButton(), but only TButton (TComponent *AOwner), TButton(void *ParentWindow) and TButton(const TButton &);
    • Any way to use operator new with arguments for TButton constructor prototypes, for an array?

• Test 2

  • Description: Creating a vector

  • Code: Also add #include "vector.h" on unit header...

    vector<TButton> Buttons;
    Buttons[0].Caption="it is ok";
    Buttons[1].Caption="mayday, mayday";
    

  • Result: Debugger exception on 3rd line:

    > Project Project1.exe raised exception class EAccessViolation
    > with message 'Acceess violation at address 401075B9 in module
    > 'vcl60.bpl'. Read of address 00000254'. Proccess stopped. Use
    > Step or Run to continue.
    

  • Comments:
    • Yeah, I expected that it would be raised, but I put it here to someone say how to allocate memory for more elements on that vector after created, since vector<TButton> Buttons(3); does not work for the same reason test1 failed :(

General question

How to do it for any visual component?

Answer 1

All of your attempts failed for the same reason - you are trying to create an array/vector of actual TButton object instances instead of an array/vector of pointers to TButton instances.

To create a fixed-length array of button pointers:

TButton* Buttons[3];
...
Buttons[0] = Button1;
Buttons[1] = Button2;
Buttons[2] = Button3;
...
for(index = 0; index < 3; ++index)
{
    TButton *Btn = Buttons[index];
    // use Btn as needed...
}

To create a dynamic-length array of button pointers:

TButton** Buttons;
...
Buttons = new TButton*[3];
Buttons[0] = Button1;
Buttons[1] = Button2;
Buttons[2] = Button3;
...
for(index = 0; index < 3; ++index)
{
    TButton *Btn = Buttons[index];
    // use Btn as needed...
}
...
delete[] Buttons;

To create a vector of button pointers:

std::vector<TButton*> Buttons;
...
Buttons.push_back(Button1);
Buttons.push_back(Button2);
Buttons.push_back(Button3);
...
for(index = 0; index < 3; ++index)
{
    TButton *Btn = Buttons[index];
    // use Btn as needed...
}
/*
Or:
for(std::vector<TButton*>::iterator iter = Buttons.begin(); iter != Buttons.end(); ++iter)
{
    TButton *Btn = *iter;
    // use Btn as needed...
}
*/

Answer 2

All this is very nice and correctly true. But I mean the user’s question was some other intention. If for all the buttons we get each of them index does no special benefit - this is only a true method: the aim is to control all components with a click (button, panels, shapes and so on…) and don’t write for each index a new code, That why I changed a few program’s code:

void __fastcall TForm1::Button1Click(TObject *Sender)

{

typedef TPanel* TPanels;

TPanels Panels[3] = {Panel1, Panel2, Panel3};

int count;

for(count=0;count<3;count++)

Panels[count]->Left=random(100);

}  

As one can see instead of index here is count. Certainly don’t forget insert randomize() to TForm1

Answer 3

Miraculous Typedef + Pseudo Array = Solution

• Miraculous Typedef:

  • After hours searching a way, I saw a typedef on that Stack Overflow and Google search journey and thought why not to:

    typedef TButton* TButtons;
    

  • Well, it changes all the things, because I could perform:

    TButtons Buttons[3];
    

• Pseudo Array:

  • The issue remained on how to allocate memory for data stored on that Buttons[3] array, but with knowledge of 2nd paragraph of Purpose section of my question, I thought: forget new data, data is there, point to there (so I call that to build a pseudo array, because I create only an array of pointers to existing data):

    TButtons Buttons[3] = {Button1, Button2, Button3};
    

  • Where Button1, Button2 and Button3 were already created when I put them on the form normally (through my mouse).

Working example

1. Create a new vcl/forms application project;
2. Put 3 buttons as those on the left on figure bellow (Button1, Button2, Button3) to demonstrate that solution, and 1 great button (Button4) also as figure bellow to do the actions;

3. Insert following code on click event of the fourth button, the great one (Button4);

   typedef TButton* TButtons;
   TButtons Buttons[3] = {Button1, Button2, Button3};
   int index;
   
   for(index=0;index<3;index++)
   {
           Buttons[index]->Caption=(AnsiString)"teste "+index+" - "+(1+random(100));
           Buttons[index]->Left=25+4*random(100);
           Buttons[index]->Top=25+4*random(100);
   }
   

4. Perform a "shazam!" run and play with that...