FIX: SetFieldNull Asserts or Crashes When Called for Parameter

ID: Q160074

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++, 32-bit Editions, version 4.2

SYMPTOMS

CRecordset::SetFieldNull() causes an assert or an access violation if called for a parameter. Even if no assert or access violation occurs, the parameter may not be set to Null.

If SetFieldNull() is called before the recordset is open, the assert occurs in DBRFX.CPP at line 48:


   ASSERT(prs->m_hstmt != SQL_NULL_HSTMT);

If SetFieldNull() is called after the recordset is open, then a call to CRecordset::Requery() may assert in DBCORE.CPP at line 4055 or line 4062:


   ASSERT(nParam < m_nParams);

If SetFieldNull() is called after the recordset is closed and before it is reopened, you will see an access violation in DBCORE.CPP at line 4057:


    m_pbParamFlags[nParam] |= AFX_SQL_FIELD_FLAG_NULL;

or at line 4064:


    m_pbParamFlags[nParam] &= ~AFX_SQL_FIELD_FLAG_NULL;

NOTE: Visual C++ 5.0 has a new function called SetParamNull() that you can use to avoid this problem.

CAUSE

SetFieldNull() in Visual C++ 4.2 was not designed to be called before calling CRecordset::Open(), and was not designed to handle parameters.

RESOLUTION

The following file is available for download from the Microsoft Software Library:

~ Paramset.exe

For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base:

Q119591 How to Obtain Microsoft Support Files from Online Services

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. The problem has been fixed with Visual C++ version 5.0 by adding a new function called SetParamNull().

MORE INFORMATION

Once you have downloaded Paramset.exe and run the EXE to extract the CParamSet class files, add CParamSet.CPP to your project.

Change your recordsets to be derived from CParamSet rather than CRecordset.

CRecordset::SetFieldNull() cannot be called before the recordset is open. If you want to call SetFieldNull() to set parameters to Null before calling CRecordset::Open(), then call CParamSet::SetParamNull() instead. You will have to change the parameters that are passed to SetParamNull() because SetFieldNull() requires a pointer to the parameter and SetParamNull() requires a zero-based index.

In your implementation of the DoFieldExchange() function, change each call to an RFX function for a parameter to a call to the corresponding Param_RFX function.

REFERENCES

Visual C++ Books Online: CRecordset::SetFieldNull

Additional query words: kbVC420bug kbDSupport assert gpf crash


Keywords          : kbfile kbDatabase kbMFC kbODBC kbVC kbVC500fix 
Version           : 4.2
Platform          : NT WINDOWS 
Issue type        : kbbug

Last Reviewed: July 27, 1999