FIX: SetFieldNull Asserts or Crashes When Called for Parameter

• The Microsoft Foundation Classes (MFC) included with: - Microsoft Visual C++, 32-bit Edition, 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);

   ASSERT(nParam < m_nParams);

    m_pbParamFlags[nParam] |= AFX_SQL_FIELD_FLAG_NULL;

    m_pbParamFlags[nParam] &= ~AFX_SQL_FIELD_FLAG_NULL;

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 (size: 21491 bytes) 

   ARTICLE-ID: Q119591
   TITLE     : 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