CDBVariant Class
Represents a variant data type for the MFC ODBC classes.
Syntax
class CDBVariant
Members
Public Constructors
| Name | Description |
|---|---|
| CDBVariant::CDBVariant | Constructs a CDBVariant object. |
Public Methods
| Name | Description |
|---|---|
| CDBVariant::Clear | Clears the CDBVariant object. |
Public Data Members
| Name | Description |
|---|---|
| CDBVariant::m_dwType | Contains the data type of the currently stored value. Type DWORD. |
Public Union Members
| Name | Description |
|---|---|
| CDBVariant::m_boolVal | Contains a value of type BOOL. |
| CDBVariant::m_chVal | Contains a value of type unsigned char. |
| CDBVariant::m_dblVal | Contains a value of type double. |
| CDBVariant::m_fltVal | Contains a value of type float. |
| CDBVariant::m_iVal | Contains a value of type short. |
| CDBVariant::m_lVal | Contains a value of type long. |
| CDBVariant::m_pbinary | Contains a pointer to an object of type CLongBinary. |
| CDBVariant::m_pdate | Contains a pointer to an object of type TIMESTAMP_STRUCT. |
| CDBVariant::m_pstring | Contains a pointer to an object of type CString. |
| CDBVariant::m_pstringA | Stores a pointer to an ASCII CString object. |
| CDBVariant::m_pstringW | Stores a pointer to a wide CString object. |
Remarks
CDBVariant does not have a base class.
CDBVariant is similar to COleVariant; however, CDBVariant does not use OLE. CDBVariant allows you to store a value without worrying about the value's data type. CDBVariant tracks the data type of the current value, which is stored in a union.
Class CRecordset utilizes CDBVariant objects in three member functions: GetFieldValue, GetBookmark, and SetBookmark. For example, GetFieldValue allows you to dynamically fetch data in a column. Because the data type of the column may not be known at run time, GetFieldValue uses a CDBVariant object to store the column's data.
Inheritance Hierarchy
CDBVariant
Requirements
Header: afxdb.h
CDBVariant::CDBVariant
Creates a NULL CDBVariant object.
CDBVariant();
Remarks
Sets the m_dwType data member to DBVT_NULL.
CDBVariant::Clear
Call this member function to clear the CDBVariant object.
void Clear();
Remarks
If the value of the m_dwType data member is DBVT_DATE, DBVT_STRING, or DBVT_BINARY, Clear frees the memory associated with the union pointer member. Clear sets m_dwType to DBVT_NULL.
The CDBVariant destructor calls Clear.
CDBVariant::m_boolVal
Stores a value of type BOOL.
Remarks
The m_boolVal data member belongs to a union. Before accessing m_boolVal, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_BOOL, then m_boolVal will contain a valid value; otherwise, accessing m_boolVal will produce unreliable results.
CDBVariant::m_chVal
Stores a value of type unsigned char.
Remarks
The m_chVal data member belongs to a union. Before accessing m_chVal, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_UCHAR, then m_chVal contains a valid value; otherwise, accessing m_chVal will produce unreliable results.
CDBVariant::m_dblVal
Stores a value of type double.
Remarks
The m_dblVal data member belongs to a union. Before accessing m_dblVal, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_DOUBLE, then m_dblVal contains a valid value; otherwise, accessing m_dblVal will produce unreliable results.
CDBVariant::m_dwType
This data member contains the data type for the value that is currently stored in the CDBVariant object's union data member.
Remarks
Before accessing this union, you must check the value of m_dwType in order to determine which union data member to access. The following table lists the possible values for m_dwType and the corresponding union data member.
| m_dwType | Union data member |
|---|---|
| DBVT_NULL | No union member is valid for access. |
| DBVT_BOOL | m_boolVal |
| DBVT_UCHAR | m_chVal |
| DBVT_SHORT | m_iVal |
| DBVT_LONG | m_lVal |
| DBVT_SINGLE | m_fltVal |
| DBVT_DOUBLE | m_dblVal |
| DBVT_DATE | m_pdate |
| DBVT_STRING | m_pstring |
| DBVT_BINARY | m_pbinary |
| DBVT_ASTRING | m_pstringA |
| DBVT_WSTRING | m_pstringW |
CDBVariant::m_fltVal
Stores a value of type float.
Remarks
The m_fltVal data member belongs to a union. Before accessing m_fltVal, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_SINGLE, then m_fltVal contains a valid value; otherwise, accessing m_fltVal will produce unreliable results.
CDBVariant::m_iVal
Stores a value of type short.
Remarks
The m_iVal data member belongs to a union. Before accessing m_iVal, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_SHORT, then m_iVal contains a valid value; otherwise, accessing m_iVal will produce unreliable results.
CDBVariant::m_lVal
Stores a value of type long.
Remarks
The m_lVal data member belongs to a union. Before accessing m_lVal, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_LONG, then m_lVal contains a valid value; otherwise, accessing m_lVal will produce unreliable results.
CDBVariant::m_pbinary
Stores a pointer to an object of type CLongBinary.
Remarks
The m_pbinary data member belongs to a union. Before accessing m_pbinary, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_BINARY, then m_pbinary contains a valid pointer; otherwise, accessing m_pbinary will produce unreliable results.
CDBVariant::m_pdate
Stores a pointer to an object of type TIMESTAMP_STRUCT.
Remarks
The m_pdate data member belongs to a union. Before accessing m_pdate, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_DATE, then m_pdate contains a valid pointer; otherwise, accessing m_pdate will produce unreliable results.
For more information about the TIMESTAMP_STRUCT data type, see the topic C Data Types in Appendix D of the ODBC Programmer's Reference in the Windows SDK.
CDBVariant::m_pstring
Stores a pointer to an object of type CString.
Remarks
The m_pstring data member belongs to a union. Before accessing m_pstring, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_STRING, then m_pstring contains a valid pointer; otherwise, accessing m_pstring will produce unreliable results.
CDBVariant::m_pstringA
Stores a pointer to an ASCII CString object.
Remarks
The m_pstringA data member belongs to a union. Before accessing m_pstringA, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_ASTRING, then m_pstringA contains a valid pointer; otherwise, accessing m_pstringA will produce unreliable results.
CDBVariant::m_pstringW
Stores a pointer to a wide CString object.
Remarks
The m_pstringW data member belongs to a union. Before accessing m_pstringW, first check the value of CDBVariant::m_dwType. If m_dwType is set to DBVT_WSTRING, then m_pstringW contains a valid pointer; otherwise, accessing m_pstringW will produce unreliable results.