Thread: Corrupted Stack...

  1. #1
    Registered User
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    Corrupted Stack...

    Hello...
    As soon as this function returns the Debug Window in VisualC++ reports this error:

    "Run-Time Check Failure #2 - Stack around the variable 'fBuffer' was corrupted."

    Code:
    int cFile::GetType(LPCWSTR filename)
    {
    	HANDLE hFile = NULL;
    	char fBuffer[3];
    	DWORD nread = 0;
    
    	hFile = CreateFile(filename, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    	if (hFile == NULL)
    		return -1;
    
    	ZeroMemory(fBuffer, sizeof(char) * 4);
    	::ReadFile(hFile, fBuffer, 4, &nread, NULL);
    	if (nread < 4)
    		return -1;
    
    	if (fBuffer[0] == 82 && fBuffer[1] == 73 && fBuffer[2] == 70 && fBuffer[3] == 70)
    		return FILE_TYPE_AUDIO;
    
    	if (fBuffer[0] == 77 && fBuffer[1] == 84 && fBuffer[1] == 104 && fBuffer[1] == 100)
    		return FILE_TYPE_MIDI;
    
    	return 0;
    }
    Why??

  2. #2
    Deathray Engineer MacGyver's Avatar
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    Because you're calling ZeroMemory() on a buffer of only 3 chars and telling it to zero out 4.

    BTW, this is the C section, and that's C++ code.

  3. #3
    Hurry Slowly vart's Avatar
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    ReadFile also uses 4 bytes buffer
    You should close the file in this function ( you do not return handle for future use)

    your use of "magic" numbers is also not too good
    All problems in computer science can be solved by another level of indirection,
    except for the problem of too many layers of indirection.
    David J. Wheeler

  4. #4
    Registered User
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    yes...you're right

    I've tried declaring fBuffer[4] instead of fBuffer[3] and everything works fine...
    Anyway shouldn't fBuffer[3] be 4 bytes long (of type char)?

    Thanks

  5. #5
    Hurry Slowly vart's Avatar
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    char array[SIZE]
    has exactly SIZE bytes... what you ask is what you get.

    Valid indexes are from 0 to SIZE-1
    All problems in computer science can be solved by another level of indirection,
    except for the problem of too many layers of indirection.
    David J. Wheeler

  6. #6
    Registered User
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    Ooops!

    I was thinking that an array had indexes from 0 to size...Well thanks a lot!

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