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Q126614: PRB: 32K Limit on Direct Parameters for 16-bit Drivers

Article: Q126614
Product(s): Open Database Connectivity (ODBC)
Version(s): WINDOWS:2.0
Operating System(s): 
Keyword(s): 
Last Modified: 12-JUN-2001

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The information in this article applies to:

- Microsoft Open Database Connectivity, version 2.0 
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SYMPTOMS
========

If you use SQLBindParameter to directly pass more than 32K of data to a SQL
statement against 16-bit desktop database drivers, you will get the following
error message:

  SQL_ERROR: Memory allocation failure.

The following is a piece of the code to duplicate the error:

     //data source is an access table objtab with only one OLE field.
     //16-bit Access driver 2.00.2317 is used

     SQLPrepare(hstmt, "insert into objtab(?)", SQL_NTS);
     BigObj = AllocateMemory(sizeof(UCHAR) * 32800);
     cbBigObj = 32800;
     SQLBindParameter(
        hstmt, 1, SQL_PARAM_INPUT, SQL_C_BINARY, SQL_C_LONGVARCHAR,
        32800, 0, BigObj, 32800, &cbBigObj);
     //Prepare the BigObj
     SQLExecute(hstmt);

Returns:

  SQL Error State:S1001; Native Error Code: 34;
  ODBC Error:[Microsoft][ODBC Microsoft Access 2.0 Driver]memory allocation
  failure.

NOTE: If cbBigObj is changed to 32750 (with corresponding changes in
SQLBindParameter), SQLExecute will succeed.

CAUSE
=====

The internal buffer for direct parameters passed to the 16-bit desktop database
drivers is limited to 32K.

NOTE: You will actually have a little less than 32K of total parameters, because
some space is taken up by a length byte in the internal buffer.

RESOLUTION
==========

- Use 32-bit drivers if you can.

- Use SQLPutData to send it in installments. Using direct parameters is not
  recommended to pass in large data. Instead, you can use data-at-execution
  with SQLPutData.

- Use SQLExtendedFetch and SQLSetPos...SQL_ADD, which is faster. Because all of
  the parameters are not copied into a separate buffer before being passed into
  the internal buffer, you save a memcopy.

Additional query words: C++ Visual Basic MSVC VB Windows NT

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbODBCSearch kbODBC200
Version           : WINDOWS:2.0
Issue type        : kbprb

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