CLongBinary Class

發行項
04/28/2015

Simplifies working with very large binary data objects (often called BLOBs, or "binary large objects") in a database.

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

CObject

CLongBinary

Requirements

Header: afxdb_.h

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