Archive bug?
Thanos Kontos -- tk4n@hti.net
Friday, April 05, 1996
VC++ 4.1/MFC 4.1/Windows95 or NT
I believe there is a bug in arccore. When a trancated file is read, MFC
ASSERTs. It should throw an exception (shouldn't it?).
This problem can be demonstrated by an AppWizard generated application,
where the serialize code is as code:
...
void CArcDoc::Serialize(CArchive& ar)
{
DWORD dw = 0;
WORD w = 0;
if (ar.IsStoring())
{
ar << dw << w; // Writes 3 bytes
}
else
{
ar >> dw;
ar >> dw; // <---- Did not get expected endOfFile Exception here
}
}
...
To work around the problem, I had to modify the 'arccore.cpp' as follows:
line 689:
// m_lpBufMax -= nUnused; // TK: Removed
m_lpBufMax = m_lpBufStart+nUnused; // TK: Added
line 693:
// UINT nRead = nUnused; // TK: Removed
UINT nRead = 0; // TK: Added
Dan Kirby -- dkirby@accessone.com
Saturday, April 06, 1996
Hi,
You are correct. This is a bug.
Your fix is fine. Note that it will not cause the exception to be thrown
on line 724 where the code reads:
// not enough data to fill request?
if ((UINT)(m_lpBufMax - m_lpBufCur) < nBytesNeeded)
AfxThrowArchiveException(CArchiveException::endOfFile);
Instead, your change will cause the exception to be thrown in the
CFile::Read.
Another interesting thing to note is that there will be times when the
exception will get thrown OK depending upon what you are storing and
reading. So for example, if you modify your example slightly:
void CArchbugDoc::Serialize(CArchive& ar)
{
DWORD dw = 0;
WORD w = 0;
BYTE ch;
if (ar.IsStoring())
{
ar << dw <> dw;
ar >> dw; // <---- Did not get expected endOfFile Exception here
}
}
This will thrown the eof exception.
--dan
----------
From: Thanos Kontos[SMTP:tk4n@hti.net]
Sent: Friday, April 05, 1996 10:08 AM
To: 'MFC List'
Subject: Archive bug?
VC++ 4.1/MFC 4.1/Windows95 or NT
I believe there is a bug in arccore. When a trancated file is read, MFC
ASSERTs. It should throw an exception (shouldn't it?).
This problem can be demonstrated by an AppWizard generated application,
where the serialize code is as code:
...
void CArcDoc::Serialize(CArchive& ar)
{
DWORD dw = 0;
WORD w = 0;
if (ar.IsStoring())
{
ar << dw << w; // Writes 3 bytes
}
else
{
ar >> dw;
ar >> dw; // <---- Did not get expected endOfFile Exception here
}
}
...
To work around the problem, I had to modify the 'arccore.cpp' as follows:
line 689:
// m_lpBufMax -= nUnused; // TK: Removed
m_lpBufMax = m_lpBufStart+nUnused; // TK: Added
line 693:
// UINT nRead = nUnused; // TK: Removed
UINT nRead = 0; // TK: Added
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