Simple C++ question -- Creating a QPoint object

[N3wb]

I was trying to set the position of my program's window and had to use a QPoint object. It's working now, but I'm a little confused on something. I first tried to create the object like this:

QPoint windowPos = new QPoint(0, 0);

QPoint windowPos = new QPoint(0, 0);

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But that gave the error:

error: conversion from `QPoint*' to non-scalar type `QPoint' requested

I was able to get it to work with this line of code:

QPoint windowPos(0, 0);

QPoint windowPos(0, 0);

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But I don't understand why the first line didn't work. I thought that was the correct method for creating an object in C++?

I would appreciate someone explaining how my thinking is wrong, thanks

[hasnatzaidi]

hi, first u tell me that in which file where you used that code.?

[lyuts]

This is not correct

QPoint windowPos = new QPoint(0, 0);

QPoint windowPos = new QPoint(0, 0);

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You create and object that is supposed to be on stack as if it were an object to be on heap. Don't mix these things.

Do it this way

QPoint *windowPos = new QPoint(0, 0);

QPoint *windowPos = new QPoint(0, 0);

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or

QPoint windowPos(0, 0);

QPoint windowPos(0, 0);

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[scascio]

Hi,

But that gave the error:

error: conversion from `QPoint*' to non-scalar type `QPoint' requested

The compiler message means that your are trying to affect a pointer to a QPoint (a QPoint*), to a QPoint. It is C++ basic features.

If you take time to decode (it is true it is not so clear as Java) messages, you'll find out what's happening

[N3wb]

So... This creates the QPoint on the heap:

QPoint *windowPos = new QPoint(0, 0);

QPoint *windowPos = new QPoint(0, 0);

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And this creates it on the stack?

QPoint windowPos(0, 0);

QPoint windowPos(0, 0);

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[scascio]

You got it

[lyuts]

Yes, this is correct.

[N3wb]

Great, thanks!

Since the QPoint is something that is just needed temporarily, would it be better to create it on the stack?

And should I always create a widget on the heap?

[scascio]

For your case you should better allocate your QPoint on the stack, cause it is small

Generally, it depends on memory management and perfomance features.

[hkvm]

N3wb: You should really get a good book on C++ first, or try Python instead with some PyQt tutorials and stuff. Jumping into C++ like this is a recipe for very poor code a LOT of frustration.

[wysota]

Since the QPoint is something that is just needed temporarily, would it be better to create it on the stack?

Always create QPoint on the stack.

And should I always create a widget on the heap?

Yes, with exception of widgets that have (and you know will always have) no parents.