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Unhandled Exception in AVIFileOpen()

Posted on 2004-08-23
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Last Modified: 2011-09-20
I'm having a problem opening an AVI file.

Using VC++ 6.0

In my header file:

protected
    PAVIFILE* m_pAviFile;



in my class constructor:

CAviFile::CAviFile()
{
    AVIFileInit();
    m_pAviFile = NULL;
..//


and then later I try to open the file:

    HRESULT hr = AVIFileOpen(m_pAviFile, m_sMoviePath, OF_WRITE | OF_CREATE, NULL);


That line crashes "Unhandled exception in MYAPP.exe [AVIFIL32.dll]: 0XC0000005: Access Violation"

The file is however being created, I can browse to the folder in windows and see it, so it's not a path problem. So what's going wrong here?

thanks
-Paul
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Question by:PMH4514
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Accepted Solution

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jkr earned 200 total points
ID: 11870586
That should be more like

protected
   PAVIFILE m_pAviFile;

    HRESULT hr = AVIFileOpen(&m_pAviFile, m_sMoviePath, OF_WRITE | OF_CREATE, NULL);

since a 'PAVIFILE *' is expected to store a PAVIFILE in there.
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Author Comment

by:PMH4514
ID: 11870720
oh duh.. damn those pointers!  

but....  wouldn't passing m_pAviFile (no ampersand) into AVIFileOpen, m_pAviFile having being defined as type PAVIFILE* be the same thing? or does "P" in "PAVIFILE" infer it's already a pointer type? (ie. I'm creating a pointer to a pointer by doing what I was doing??)

anyway - I made that change, and AVIFileOpen is no longer crashing. but now I'm getting the same error on this line:

HRESULT hr = AVIFileCreateStream(m_pAviFile, &m_psWrite, &strhdr);

where m_psWrite is defined in the header:
PAVISTREAM m_psWrite

and strhdr is defined locally within my method:

AVISTREAMINFO strhdr;
memset(&strhdr, 0, sizeof(strhdr));
strhdr.fccType                = streamtypeVIDEO;   // stream type
// etc..


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LVL 86

Expert Comment

by:jkr
ID: 11870759
>>or does "P" in "PAVIFILE" infer it's already a pointer type?

Yes, these are MS' naming conventions.

>>now I'm getting the same error on this line:
>>HRESULT hr = AVIFileCreateStream(m_pAviFile, &m_psWrite, &strhdr);

Hm, that actually looks good. Have you tried to

ASSERT(m_pAviFile);
HRESULT hr = AVIFileCreateStream(m_pAviFile, &m_psWrite, &strhdr);

?
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Author Comment

by:PMH4514
ID: 11870767
actually, I think the CreateStream is crashing because my AVIFileOpen is still not working properly. I don't crash with the access violation, but the pointer remains NULL, and the result equals a long negative number..

(the fact that my code got to my AVIFileCreateStream() call in that state means I need better error trapping, but that's offtopic)

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Author Comment

by:PMH4514
ID: 11870793
looks like we were typing at the same time..  I guess the problem is still that AVIFileOpen() isn't properly returning the file handle (though again, the file is being created, I see it in windows explorer)
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LVL 86

Expert Comment

by:jkr
ID: 11871059
Are you sure you are filling in the header correctly? The sample at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/multimed/htm/_win32_reading_from_one_stream_and_writing_to_another.asp ("Reading from One Stream and Writing to Another") illustrates how to use these APIs, and they're doing it exactly the same way.
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Author Comment

by:PMH4514
ID: 11871062
Oh duh, once again I forgot to call CoInitialize()..

it's all set now, thanks!
-Paul
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