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-   -   Qt: ridiculous behaviour (https://talk.maemo.org/showthread.php?t=49468)

gri 2010-05-19 07:57
Re: Qt: ridiculous behaviour
 
Parent can be any class that inherits from QObject. QWidgets are inherited from QObject, so yes.
If you create a dialog, give all member pointer variables the dialog as parent and you don't have to care about their memory :)
With Qt the memory handling is a lot easier than with blank c++.

PS: You could also take a look at QSharedPointer when using non-QObject classes. (or boost::shared_ptr if you don't like the Qt implementation)

attila77 2010-05-19 08:08
Re: Qt: ridiculous behaviour
 
Qt also provides some convenience classes for people wishing more pointer automatism:

http://doc.qt.nokia.com/4.6/qscopedpointer.html

http://doc.qt.nokia.com/4.6/qsharedpointer.html

Not exactly garbage collection, but it's as close as it gets to it in 'standard' C++.

saxen 2010-05-19 08:38
Re: Qt: ridiculous behaviour
 
Quote:
Originally Posted by gri (Post 665586)
Parent can be any class that inherits from QObject. QWidgets are inherited from QObject, so yes.
If you create a dialog, give all member pointer variables the dialog as parent and you don't have to care about their memory :)
With Qt the memory handling is a lot easier than with blank c++.
so in constructor method i've to define:

className(parameters, QObject parent);

am i right?

gri 2010-05-19 08:45
Re: Qt: ridiculous behaviour
 
Quote:
Originally Posted by saxen (Post 665640)
so in constructor method i've to define:

className(parameters, QObject parent);

am i right?
Not sure what you mean.

example implementation code:
Code:
MyClass::MyClass(QObject* parent)
: QObject(parent) // Not passing the parent to the QObject base will also result in memory leakage
{
    mySubObject = new QObject(this); // Will be deleted when "MyClass" dies
    myLeakObject = new QObject; // Will live forever
}

saxen 2010-05-19 08:53
Re: Qt: ridiculous behaviour
 
Quote:
Originally Posted by gri (Post 665655)
Not sure what you mean.

example implementation code:
Code:
MyClass::MyClass(QObject* parent)
: QObject(parent) // Not passing the parent to the QObject base will also result in memory leakage
{
    mySubObject = new QObject(this); // Will be deleted when "MyClass" dies
    myLeakObject = new QObject; // Will live forever
}
yes, that's what i meant!! really thanks :)

saxen 2010-05-19 13:46
Re: Qt: ridiculous behaviour
 
while i'm bothering you with this silly questions, i've another doubt about inclusions :o

how to use #include? i mean it's different from java import, so using include(from what i remember) means include "piece of code"(correct if i'm wrong) and not just import a name space!

so, how to avoid duplicate include?
suppose i have main class, firstclass and secondclass, if i include secondclass in firstclass, and first class in main, does main class automatically include secondclass?

i hope u can understand what i'm trying to say :o

damnshock 2010-05-19 14:27
Re: Qt: ridiculous behaviour
 
Quote:
Originally Posted by saxen (Post 666061)
while i'm bothering you with this silly questions, i've another doubt about inclusions :o

how to use #include? i mean it's different from java import, so using include(from what i remember) means include "piece of code"(correct if i'm wrong) and not just import a name space!

so, how to avoid duplicate include?
suppose i have main class, firstclass and secondclass, if i include secondclass in firstclass, and first class in main, does main class automatically include secondclass?

i hope u can understand what i'm trying to say :o
#include is macro directive, an it does what it says: *includes*. You'll make your program bigger in size


#ifndef H_WHATEVER
#define H_WHATEVER


//CODE

#endif

Does this solve your problem?

PS:I'm too learning C++ to develop with Qt :)

gri 2010-05-19 17:11
Re: Qt: ridiculous behaviour
 
You can also use "#pragma once" instead of the ifndef guards. But this is not supported by every compiler.
So with ifndefs you are on the safe side, with pragma once you type less ... of course, you could also use both of them in one file.

Joorin 2010-05-19 18:50
Re: Qt: ridiculous behaviour
 
Compilation of C++ (and C) happens in a couple of different steps:

- Preprocessor (handles #include, #define, #if, #ifdef and the like)
- Compiler (parses all the code and builds an abstract representation, AST, that's then changed in different ways for some kinds of optimization and other compiler magic)
- Generate assembler (the compiler backend translates the AST to platform specific assembler)
- Assembler (the assembler read the assembly code and translates it into object code with link references as special markers)
- Linker (links the compilation units (object code blobs) together and fixes link markers to reference shared libraries)

The preprocessor can be thought of as just a file manipulator that puts together the file that is to be parsed by the compiler. #include is a character by character insertion of another file.

As explained above, #ifdef is the classical way of preventing multiple includes.


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