theApp vs. AfxGetApp() - does it matter?

[DalTXColtsFan]

Greetings all,
In some MFC samples I see the use of AfxGetApp() to get a pointer to the main app class, in others I see theApp.

Are there any good reasons to use one over the other?

Thanks
Joe

[proxima centaur]

theApp is the variable created by the VC wizard.
AfxGetApp returns the same instance.

Use either one.

[ergas]

I think not. Both are the same.

The reason to use AfxGetApp() is, it is global. You can access it from anywhere in your application, while theApp is defined and accessible only inside the application class.

[galathaea]

Originally posted by ergas
The reason to use AfxGetApp() is, it is global. You can access it from anywhere in your application, while theApp is defined and accessible only inside the application class.

theApp is instantiated in the global space as well.

[DalTXColtsFan]

Originally posted by galathaea

theApp is instantiated in the global space as well.

Yeah, I noticed that, but still, you have to add an extern line to YourApp.h because it's declared in YourApp.cpp. Still though, seems like there's not a lot of difference.

[Andreas Masur]

Well...simplified

CWinApp *AfxGetApp() { return &theApp; }

so...no real difference...

[Ajay Vijay]

Originally posted by Andreas Masur
Well...simplified

CWinApp *AfxGetApp() { return theApp; }

so...no real difference...

I think that code should be:

CWinApp *AfxGetApp() { return &theApp; }

Thanx

[Andreas Masur]

Originally posted by Ajay Vijay
I think that code should be:

CWinApp *AfxGetApp() { return &theApp; }

Thanx

Yep...thank you for your attention...

[0xC0000005]

AfxGetApp() is actually defined as below (simplified) which could make a big difference if you are working with DLL's or possibly other unknown 'module state' situations.

CWinApp* AfxGetApp()
{
AfxGetModuleState()->m_pCurrentWinApp;
}

[Andreas Masur]

Originally posted by 0xC0000005
AfxGetApp() is actually defined as below (simplified) which could make a big difference if you are working with DLL's or possibly other unknown 'module state' situations.

CWinApp* AfxGetApp()
{
AfxGetModuleState()->m_pCurrentWinApp;
}

Well...that is the complete implementation of the function...however my intention was to keep things simplified to the OP and to show that there is basically no difference between using the function and/or 'theApp'...

[JamesB43]

I think there is a significant difference. Using theApp will be quicker because it doesn't require any function calls, however, it is less portable. So if you are coding something you plan to re-use, you are better off with AfxGetApp().

James

[Andreas Masur]

Originally posted by JamesB43
I think there is a significant difference. Using theApp will be quicker because it doesn't require any function calls, ....

Not necessarely...the functions are implemented as inline functions therefore you will not have any difference in speed...depending on the compiler of course. However, even a function call would not add that much time these days...

[IndikaNiva]

who cares..
Just use one of them!!!

[darwen]

You can use AfxGetApp in libraries to get hold of the application object where you can't include the .h file for the application.

I know, I've got loads of classes in libraries which do this.

Apparently you can also have COM objects which when AfxGetApp is called return the main application object, not the application object in the COM dll. Don't know how to do it though - but the Visual C++ addin dlls created by ClassWiz seem to be able to do this.

Darwen.

[Ajay Vijay]

Originally posted by Andreas Masur
Not necessarely...the functions are implemented as inline functions therefore you will not have any difference in speed...depending on the compiler of course. However, even a function call would not add that much time these days...

Function calls does not matter now days? Are you sure? Have you seen the coding, by tracing, behind the AfxGetApp? Well that's a complex one. So it is better to use 'theApp' directly if call is from same executable or use it once store it in a CWinApp pointer, if desired on other executable (DLL for example - on which your app is dependent).