DOCUMENT:Q156134  30-JUL-2001  [visualc]
TITLE   :FIX: CLongBinary Causes "Invalid String or Buffer Length"
PRODUCT :Microsoft C Compiler
PROD/VER:4.0 4.1 4.2
OPER/SYS:
KEYWORDS:kbDatabase kbMFC kbODBC kbVC kbVC500fix

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The information in this article applies to:

 - The Microsoft Foundation Classes (MFC), included with:
    - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
    - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
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SYMPTOMS
========

When updating CLongBinary data using CRecordset::Update(), you may receive the
error "Invalid string or buffer length."

CAUSE
=====

MFC's RFX_LongBinary function uses an obsolete method to specify the size of the
field when binding the CLongBinary buffer for the update. MFC specifies that the
length of the long binary field is SQL_DATA_AT_EXEC, a symbol that signifies
that data is transferred via SQLPutData() without providing any information
about the field's size.

The following is true according to the documentation for SQLExecDirect (Problems
and Information) in the ODBC SDK 2.10 Release Notes, included with VC++ 4.1:

   

   SQLSTATE S1090 (Invalid string or buffer length):
   A parameter length value bound by SQLBindParameter was set to
   SQL_DATA_AT_EXEC; the SQL type was either SQL_LONGVARCHAR,
   SQL_LONGVARBINARY, or a long, data-source specific data type; and the
   SQL_NEED_LONG_DATA_LEN information type in SQLGetInfo was "Y."

The 32-bit Intersolve 2.11 Oracle 7 ODBC driver for NT and Windows 95 returns
this error, which may also be returned by other ODBC drivers that meet the above
criteria.

RESOLUTION
==========

To avoid this error, you can modify MFC to use the SQL_LEN_DATA_AT_EXEC() macro
that provides information about the size of the data and thereby allows the
driver to perform the update.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in Visual C++ version 5.0.

MORE INFORMATION
================

The following steps detail one method of making the needed changes in
RFX_LongBinary:

1. Copy the implementation of RFX_LongBinary() (Msdev\Mfc\Src\Dbrfx.cpp) into a
   new .cpp file, and rename the function to something like RFX_LongBinary2().
   Create a header file for the .cpp file and include that in your recordset
   .cpp file. Be sure to #include "stdafx.h" at the top of your new .cpp file
   and include the .cpp file in your project.

2. Change all RFX_LongBinary() calls in your recordset's DoFieldExchange() to
   calls to RFX_LongBinary2().

3. In your new RFX_LongBinary2() implementation, copy the following code that
   appears under "case CFieldExchange::SetFieldNull":

         // Length is signed value, it's limited by LONG_MAX
         if (value.m_dwDataLength >
             (ULONG)(LONG_MAX - labs(SQL_LEN_DATA_AT_EXEC_OFFSET)))
         {
            ASSERT(FALSE);
            *plLength = LONG_MAX - labs(SQL_LEN_DATA_AT_EXEC_OFFSET);
         }
         else
            *plLength = value.m_dwDataLength;

         *plLength = SQL_LEN_DATA_AT_EXEC(*plLength);

   Paste this code over the line that contains SQL_DATA_AT_EXEC in the following
   code, which appears under "case CFieldExchange::Value":

         {
            // Indicate data will be sent after SQLExecute
            *plLength = SQL_DATA_AT_EXEC;       << REPLACE THIS LINE
         }

   This causes the macro to be used instead of the constant.

4. In the CFieldExchange::SetFieldNull case, you can simply comment out the
   conditional that currently causes the macro to be used only in those cases
   where m_bUseUpdateSQL is FALSE. Comment out a total of five lines as noted
   below:

        if (pFX->m_prs->m_bUseUpdateSQL)      // COMMENT OUT THIS LINE
           *plLength = SQL_DATA_AT_EXEC;      // COMMENT OUT THIS LINE
        else                                  // COMMENT OUT THIS LINE
        {                                     // COMMENT OUT THIS LINE
           // Length is signed value, it's limited by LONG_MAX
           if (value.m_dwDataLength >
               (ULONG)(LONG_MAX - labs(SQL_LEN_DATA_AT_EXEC_OFFSET)))
           {
              ASSERT(FALSE);
              *plLength = LONG_MAX - labs(SQL_LEN_DATA_AT_EXEC_OFFSET);
           }
           else
              *plLength = value.m_dwDataLength;

           *plLength = SQL_LEN_DATA_AT_EXEC(*plLength);
        }                                     // COMMENT OUT THIS LINE

REFERENCES
==========

ODBC Programmer's Reference
ODBC SDK 2.10 Release Notes

Additional query words: kbVC400bug Intersolv Oracle

======================================================================
Keywords          : kbDatabase kbMFC kbODBC kbVC kbVC500fix 
Technology        : kbAudDeveloper kbMFC
Version           : 4.0 4.1 4.2
Issue type        : kbbug
Solution Type     : kbfix

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