Q125465 - FIX: Floating Point Field Incorrectly Assigned -9.123E+19

FIX: Floating Point Field Incorrectly Assigned -9.123E+19

Q125465

1.51 1.52 WINDOWS kbprg kbbuglist kbfixlist --------------------------------------------------------------------- The information in this article applies to: - The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++ for Windows, versions 1.51 and 1.52 --------------------------------------------------------------------- SYMPTOMS ======== When you use the RFX_Single() function and set a field to null, the field may actually be set to -9.123E+19 rather than null. For example, the following code doesn't set the field to null as expected. CYourRecordset rs; rs.Open(); rs.Edit(); rs.SetFieldNull(&rs.m_floatfield); rs.Update(); rs.Close(); CAUSE ===== The problem is caused by a bug in the MFC database classes. Specifically, the RFX_Single() function performs an incorrect check to see if a field is null. Looking at DBFLT.CPP in the MSVC15\MFC\SRC directory, you'll see this: case CFieldExchange::MarkForUpdate: if (value != AFX_RFX_SINGLE_PSEUDO_NULL) pFX->m_prs->ClearFieldFlags(nField, AFX_SQL_FIELD_FLAG_NULL, pFX->m_nFieldType); goto LDefault; The code doesn't work correctly because AFX_RFX_SINGLE_PSEUDO_NULL is defined in AFXDB.H as this: #define AFX_RFX_SINGLE_PSEUDO_NULL (-9.123e19) It should be defined as this: #define AFX_RFX_SINGLE_PSEUDO_NULL (-9.123e19f) As you can see the code compares a float to a double, so the comparison will never be true. RESOLUTION ========== To work around this problem, follow these steps: 1. Copy the RFX_Single() function from DBFLT.CPP into the CRecordset's .CPP file and rename the function to something like RFX_Single2. 2. Include the following code before the RFX_Single2() function: #undef AFX_RFX_SINGLE_PSEUDO_NULL #define AFX_RFX_SINGLE_PSEUDO_NULL (-9.123e19f) 3. Change the call to RFX_Single() in the CRecordset's DoFieldExchange() function to RFX_Single2(), and move the function call out of the ClassWizard tagged section. The ClassWizard tagged section is the region between: //{{AFX_FIELD_MAP(CYourRecordset) and: //}}AFX_FIELD_MAP NOTE: the problem does not occur when using RFX_Double, so if you can use a double field type in your database, use RFX_Double to avoid the problem. STATUS ====== Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in Microsoft Visual C++, 32-bit Edition, version 2.2. Additional reference words: 1.51 1.52 2.51 2.52 ODBC numeric number KBCategory: kbprg kbbuglist kbfixlist KBSubcategory: MfcDatabase

Keywords : kb16bitonly kbDatabase kbMFC kbODBC kbVC
Issue type :
Technology : kbAudDeveloper kbMFC