[egenix-users] Null termination differences in drivers - comment in mxODBC.c

[M.-A. Lemburg]

M.-A. Lemburg wrote:
> Martin J. Evans wrote:
> 
>> Could anyone explain the origin of the following comment in mxODBC.c
>> (specifically the reference to the Easysoft Oracle driver)?
> 
> 
> We had to add that work-around to make mxODBC work with the
> EasySoft Oracle driver 1.0.0.6. Things may be different with
> more recent versions. The work-around adapts accordingly.
> 
>> How do you reproduce this?
> 
> 
> Simple: query a BLOB of say 1MB data from the database.

Sorry: make that CLOB (the problem only triggers for character
data such as XML data).

>> Thanks.
>>
>>             if (null_terminated) {
>>                 /* Remove null termination; various ODBC drivers have 
>> bugs
>>                    in the way the handle null-termination:
>>
>>                    * EasySoft ODBC for Oracle does not null-terminate 
>> character
>>                      columns, even though it should
>>
>>                    * MS SQL Server ODBC always null-terminates Unicode 
>> columns
>>                      with two nulls, even when fetching the data as 
>> SQL_C_CHAR
>>                      where it should only append one null-termination 
>> character
>>
>>                    The ODBC standard is unclear about what to do, but
>>                    using sizeof(SQLWCHAR) seems to work in most
>>                    cases. We have to careful here, since some database
>>                    drivers allow passing binary data back through
>>                    character columns, so embedded nulls are well
>>                    possible.
>>
>>                    Thanks to Tommi Auvinen for helping to track down
>>                    the MS SQL Server problem.
>>
>>                 */
>>                 char *data = (char *)newdata;
>>                 int endofdata = offset + received - 1;
>>                 if (data[endofdata] == '\0') {
>>                     received--;
>> #ifdef SQL_WCHAR
>>                     if (data[endofdata - 1] == '\0') {
>>                         if (var->ctype == SQL_C_WCHAR ||
>>                             var->sqltype == SQL_WCHAR ||
>>                             var->sqltype == SQL_WVARCHAR ||
>>                             var->sqltype == SQL_WLONGVARCHAR)
>>                             received -= sizeof(SQLWCHAR) - 1;
>>                     }
>> #endif
>>                 }
>>             }
>>
>>
>> -- 
>> Martin J. Evans
>> Easysoft Ltd, UK
>> Development
>>
>>
>> _______________________________________________________________________
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>> http://lists.egenix.com/mailman/listinfo/egenix-users
> 
> 

-- 
Marc-Andre Lemburg
eGenix.com

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