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CArchive BUG

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Take a look at the following code. Can you see the problem? The code crashes and burns if the socket 'socketFile' is attached to has its terminating socket closed. If the MFC developers would have followed standard guidelines for exception handling, everything would be fine. RULE: Never throw exceptions from destructors.


bool sendObject(CObject* pObj)
{
	other code ...

	CArchive ar(&socketFile, CArchive::store);

	ar << pObj;
	ar.Flush();
	ar.Close();

	... other code
}

void someOtherFunction()
{
	MyObject obj;

	bool bSuccess = false;
	try
	{
		bSuccess = sendObject(&obj);
	}
	catch (CException* pEx)
	{
		pEx->Delete();
	}
}

The Scenario:

Archiving an object to a CSocketFile that may have had the terminating socket closed.

The Result:

If the terminating socket has been closed, calling Flush on the CArchive will raise an exception (so will calling Close). In the previous case, before the exception is handled, CArchive goes out of scope and its destructor calls Close. Close throws another exception and all hell breaks loose. Never throw exceptions from destructors.

You will need nested try / catch blocks ...


bool sendObject(CObject* pObj)
{
	other code ...

	CArchive ar(&socketFile, CArchive::store);

	try
	{
		ar << pObj;
		ar.Flush();
		ar.Close();
	}
	catch (CException* pEx)
	{
		pEx->Delete();
		return false;
	}

	... other code
}

someOtherFunction()
{
	MyObject obj;

	bool bSuccess = false;
	try
	{
		bSuccess = sendObject(&obj);
	}
	catch (CException* pEx)
	{
		pEx->Delete();
	}
}



This article was originally published on February 13th, 1999

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