array already filled? 1

[russland]

Hi,

QUESTION #1
Header:
QPushButton *pbArray[3][3];

CPP:
pbArray[3][3] = new QPushButton(this);

How can I check if I've already put a QPushButton into an array as I just did in the cpp file (pbArray[3][3] = new QPushButton(this)?

I need to know because IF then I would loop and delete (deconstruktor) all objects (GUIs) in order to remove them from the screen.

QUESTION #2
Is there a better way to remove GUI objects/widgets in C++ from the parent widget than looping end 'deconstruct'?

 

[cpjust]

Set all pointers in the array to NULL before using them.

 

[uolj]

Question #1: Your array holds pointers that are probably not initialized. Valid subscripts are [0][0], [0][1], [0][2], [1][0], [1][1], [1][2], [2][0], [2][1], and [2][2]. The [3][3] position that you attempted to use is out of bounds of the array and will probably lead to a crash.

As for your real question, the best way to do this would be to initialize the contents of the array to 0 (null pointers). Then after you have added a couple QPushButtons to the array you can check to see if the pointer is 0 to know whether you have added the QPushButton to that location. When you delete the pointers in the array, it is safe to delete a null pointer, so you don't even have to check at that point if you initialize them all to null in the beginning.

 

[russland]

set them to null works like this?
pbArray[3][3] = null;

any clue on how to verify if there something inside?

 

[russland]

okay
- i checked for 0 (not null)
- i hide it (hide())
- i set it to 0

do I still have to "destruct" it after setting it to 0?

Thanks to both of you.

 

[uolj]

No, the code you added again accesses memory outside the bounds of the array.

To set them all to null you could do several things depending on whether this array is a member of a class or a global variable, etc. Hopefully it is a member of the class. If it is, then you would make a double loop that sets each member to 0. In C++, null is not a valid keyword. Some people use NULL, but using 0 is probably the best way:

for (int i = 0; i < 3; ++i) {
  for (int j = 0; j < 3; ++j) {
    pbArray[i][j] = 0;
  }
}

 

[uolj]

My "no" answer was to your previous post.

If you allocate memory with new, then you have to delete that memory by calling delete. If you just set the pointer to 0 instead of deleting it, then you have a memory leak.

 

[cpjust]

You could also set them all to NULL like this:

memset( pbArray, NULL, sizeof( pbArray ) );

 

[ArkM]

cpjust,
some remarks: it's unportable way to initialize pointers via memset instead of explicit null pointer assignment (better 0 than old NULL).
A null pointer may have not-null bits representation...