Access C++ Interface from Fortran

[christianh]

Hi gents.

I'm working on a problem and it costs me several hours without getting an idea how to solv it. I have the following problem.

I want to create a avi, therefore I use the vfw32.lib. Unfortunately the whole interface stuff is missing, so I took a look at the vfw.h file andrebuiltthe nesseccary functions and typesby myself. I made it so far that I can open a file, choose a compressor and its settings, but I'm not able to Set these settings. I played a little bit around and come to the point, where I think that I figured out the problem. I used the following functions from the MSDN library

FORTRAN SOURCE CODE:
************************************************************
// OPEN THE FILE - THIS WORKS FINE

iret = AVIFileOpen(loc(m_pAVIFile), loc('d:TEST.avi' // char(0)), OF_READ, NULL)

// retrieve the information about the file - THIS CAUSES THE PROGRAM TO CRASH

iret = AVIFileInfo(m_pAVIFile, loc(STavifileinfo),sizeof(STavifileinfo))
****************************************************************

C++ SOURCE CODE:
*************************************************************
hr = AVIFileOpen(&m_pAVIFile,"D:\Test.avi",OF_READ,NULL);

hr = AVIFileInfo(m_pAVIFile,&filHdr,sizeof(filHdr));
*************************************************************

The C++ Code works fine. I think my problem is, that refering to the MSDN library m_pAVIFile is a

"Pointer to a buffer that receives the new IAVIFile interface pointer"

And if you take a deeper look at IAVIFile interface:

"The IAVIFile interface supports opening and manipulating files and file headers, and creating and obtaining stream interfaces. Uses IUnknown::QueryInterface, IUnknown::AddRef, and IUnknown::Release in addition to the following custom methods:

Method	Description
CreateStream	Creates a stream for writing.
EndRecord	Writes the "REC" chunk in a tightly interleaved AVI file.
GetStream	Opens a stream by accessing it in a file.
Info	Fills and returns an AVIFileInfo structure with information about a file.
Open	Initializes a file handler.
ReadData	Reads file headers data, format data, or nonaudio and nonvideo data.
WriteData	Writes file headers data, format data, or nonaudio and nonvideo data. "

I think that the Function AVIFileInfo somehow tries to call the Info function of this IAVIFile interface, But due to the fact that Fortan has no information about the further methods of this "virtual class", it causes the code to crash if I try to access one of these methods.

Now finally my question.

Has anybody an Idea how I can solve this problem. Like is there a possibility to create classes in FORTRAN?
How can I access the functions of the interface directly?
Or is there an easier way to create an AVI?

Many thanks,

Christian

[joerg_kuthe]

What type are you using for this variable named m_pAVIFile?

Joerg Kuthe

www.qtsoftware.de

[Lars_Jakobsen]

Hi

I am struggling with the same question as Christian i.e. I want to access the AVIfunction from vfw32.lib. Realizing that there do not seem to be an fortran interface to vfw32.lib I tried to create one myself using the vfw.h file and samples that demonstrate how this was accomplished in e.g. VB. However I am not able to make a doable interface, and get an "access violation" when trying to use AVIFILEOPEN.

My code so far is:

interface AVIFileOpen

function AVIFileOpen_G(ppfile, szFile, uMode, lpHandler)

USE DFWINTY

integer :: AVIFileOpen_G !STDAPI

!DEC$ ATTRIBUTES DEFAULT, STDCALL, DECORATE, ALIAS:'AVIFileOpen' :: AVIFileOpen_G

integer(POINTER_LEN) ppfile !PAVIFILE * ppfile (Should this be a pointer?)

character*(*) szFile !LPCTSTR szFile

integer(UINT) uMode !UINT umode

!DEC$ ATTRIBUTES REFERENCE, ALLOW_NULL :: lpHandler

integer(POINTER_LEN) lpHandler !CLSID * pclsidHandler (Should this be a pointer?)

end function

end interface

...

and the calling sequence that produce the error

fOk = AVIFileOpen(loc(avifile), 'c:test.avi'C, OF_CREATE,NULL)

can anybody offer any help?

Regards

Lars

[IanH]

I think you might need a !DEC$ ATTRIBUTES REFERENCE :: szFile in there.

[Lars_Jakobsen]

Thank you - my application now makes avi files :)

Regards
Lars