Q182386: PRB: Varchar Output Parameter Causes "Data Truncated" Error

Article: Q182386
Product(s): Microsoft C Compiler
Version(s): WINNT:5.0
Operating System(s): 
Keyword(s): kbDatabase kbMFC kbODBC kbVC
Last Modified: 17-JUL-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
- Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
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SYMPTOMS
========

When using MFC ODBC to call a Microsoft SQL Server stored procedure that returns
a CHAR or VARCHAR output parameter, the buffer intended to hold the data
returned will be Null and ODBC will return the error:

  

  Warning: ODBC Success With Info, Data truncated
  State:01004,Native:0,Origin:[Microsoft][ODBC SQL Server Driver]

CAUSE
=====

This problem is caused by the way that parameters are bound in the RFX_Text
function. The call to SQLBindParameter appears as follows:

     AFX_SQL_SYNC(::SQLBindParameter(pFX->m_hstmt, (UWORD)nField,
      (SWORD)pFX->m_nFieldType, SQL_C_CHAR, (SWORD)nColumnType,
      nMaxLength, nScale, pvParam, 0, plLength));

The problem is the next to the last parameter, the cbValueMax argument, which is
hard coded to 0 (zero). The cbValueMax argument specifies the length of the
buffer; it applies only to character data, not to numerics. If the number of
bytes available to return is greater than or equal to this number, then the
driver truncates it to cbValueMax-1 and null terminates it (and throws the error
above). Because the parameter is hard coded to 0, the error will always be
returned.

RESOLUTION
==========

The resolution is to copy the RFX_Text function from Dbrfx.cpp and paste it into
your project. Give it a name, such as RFX_TextOut, and then locate the
SQLBindParameter call in question (right below the first UNICODE section).
Change the SQLBindParameter call to the following:

     AFX_SQL_SYNC(::SQLBindParameter(pFX->m_hstmt, (UWORD)nField,
     (SWORD)pFX->m_nFieldType, SQL_C_CHAR, (SWORD)nColumnType,
     nMaxLength, nScale, pvParam, nMaxLength, plLength));

By using the nMaxLength input parameter, the new RFX_Text function allows the
driver to set up a buffer of the correct size for the text Output parameter.

STATUS
======

Microsoft is researching this problem and will post new information here in the
Microsoft Knowledge Base as it becomes available.

Additional query words:

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Keywords          : kbDatabase kbMFC kbODBC kbVC 
Technology        : kbVCsearch kbAudDeveloper kbVC500 kbVC32bitSearch kbVC500Search
Version           : WINNT:5.0
Issue type        : kbprb

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