Two ways, Which one is better?

[HelloDan]

Hello! Long time no see!

The following two fragments, which is better, why?

void oneDialog::function()
{
  QTestDialog* pt= new QTestDialog(this);
  // ........
  delete pt;
}
 
 
 
void oneDialog::function()
{
  QTestDialog dialog(this);
  // ........
 
}

void oneDialog::function()
{
  QTestDialog* pt= new QTestDialog(this);
  // ........
  delete pt;
}



void oneDialog::function()
{
  QTestDialog dialog(this);
  // ........
 
}

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Thanks!

[wysota]

What do you mean "better"? They are perfectly equivalent. The second one is less code to type in. If that counts as "better" then it's better.

[talk2amulya]

hey, i was wondering if in the second fragment, its done wrongly. cuz 'this' has been set as the parent of the dialog and as every parent deletes its childs when deleting themselves, when it will try to delete the dialog , the app should crash cuz the dialog is actually created on stack..

[HelloDan]

hey, i was wondering if in the second fragment, its done wrongly. cuz 'this' has been set as the parent of the dialog and as every parent deletes its childs when deleting themselves, when it will try to delete the dialog , the app should crash cuz the dialog is actually created on stack..

You mean that the dialog should be a modal one?

[talk2amulya]

no, that wont make difference..all i mean is widgets and dialogs should always be created on heap..AFAIK

[wysota]

no, that wont make difference..all i mean is widgets and dialogs should always be created on heap..AFAIK

No, that's not true. A modal dialog will always be destroyed before its parent. Unless of course you explicitely shoot yourself in the leg but then the dialog shouldn't have been modal. It really doesn't matter which way you choose here. The stack based version is simply a few statements shorter to code and a tiny bit faster to execute.

[talk2amulya]

so will that concept apply even in the case of a normal dialog(non-modal)?

[lni]

One goes out of scope by itself, one doesn't automatically go out of scope...

If it is a modal dialog, the 2nd one works as good as the 1st one but with less codes... You can't say one is better than the other, it depends on situation...

[HelloDan]

Does this forum has any utilities to save a thread, such add to favouites?

[wysota]

so will that concept apply even in the case of a normal dialog(non-modal)?

No. A non-modal dialog has to be created on heap.

Does this forum has any utilities to save a thread, such add to favouites?

Yeah, there is a "Bookmarks" table at the bottom of the page.

[talk2amulya]

ok, so that means when i have a model dialog on STACK with another widget as parent..thats not wrong? one would think it should be...when parent will try to delete it, it should be crashing time..or am i getting smth really wrong about model dialog??.or maybe u can create a model dialog on stack and not give it a parent..in these examples, 'this' is parent, so be a dialog model or not, dialog creation on stack should be wrong.

[ktk]

What do you mean "better"? They are perfectly equivalent. The second one is less code to type in. If that counts as "better" then it's better.

It also use one allocation less and has a slightly better chance to be exception save. I can't think of any situation where the first form is better.

[wysota]

This is really an academic talk. One allocation more or less doesn't make a difference, Qt doesn't use exceptions so only your code can be throwing one so you should know how/where to catch it, etc. These two are practically equivalent, the stack based is simpler to type in which is completely meaningless as well. There is a potential situation when a heap based dialogue would lead to a memory leak but then read my post about "enlightened users"