CLongBinary Class
Simplifies working with very large binary data objects (often called BLOBs, or "binary large objects") in a database.
Syntax
class CLongBinary : public CObject
Members
Public Constructors
| Name | Description |
|---|---|
| CLongBinary::CLongBinary | Constructs a CLongBinary object. |
Public Data Members
| Name | Description |
|---|---|
| CLongBinary::m_dwDataLength | Contains the actual size in bytes of the data object whose handle is stored in m_hData. |
| CLongBinary::m_hData | Contains a Windows HGLOBAL handle to the actual image object. |
Remarks
For example, a record field in a SQL table might contain a bitmap representing a picture. A CLongBinary object stores such an object and keeps track of its size.
Note
In general, it is better practice now to use CByteArray in conjunction with the DFX_Binary function. You can still use CLongBinary, but in general CByteArray provides more functionality under Win32, since there is no longer the size limitation encountered with 16-bit CByteArray. This advice applies to programming with Data Access Objects (DAO) as well as Open Database Connectivity (ODBC).
To use a CLongBinary object, declare a field data member of type CLongBinary in your recordset class. This member will be an embedded member of the recordset class and will be constructed when the recordset is constructed. After the CLongBinary object is constructed, the record field exchange (RFX) mechanism loads the data object from a field in the current record on the data source and stores it back to the record when the record is updated. RFX queries the data source for the size of the binary large object, allocates storage for it (via the CLongBinary object's m_hData data member), and stores an HGLOBAL handle to the data in m_hData. RFX also stores the actual size of the data object in the m_dwDataLength data member. Work with the data in the object through m_hData, using the same techniques you would normally use to manipulate the data stored in a Windows HGLOBAL handle.
When you destroy your recordset, the embedded CLongBinary object is also destroyed, and its destructor deallocates the HGLOBAL data handle.
For more information about large objects and the use of CLongBinary, see the articles Recordset (ODBC) and Recordset: Working with Large Data Items (ODBC).
Inheritance Hierarchy
CLongBinary
Requirements
Header: afxdb_.h
CLongBinary::CLongBinary
Constructs a CLongBinary object.
CLongBinary();
CLongBinary::m_dwDataLength
Stores the actual size in bytes of the data stored in the HGLOBAL handle in m_hData.
SQLULEN m_dwDataLength;
Remarks
This size may be smaller than the size of the memory block allocated for the data. Call the Win32 GLobalSize function to get the allocated size.
CLongBinary::m_hData
Stores a Windows HGLOBAL handle to the actual binary large object data.
HGLOBAL m_hData;