[freetds] no conversion changes...: Unicode with UTF-8 or

Sebastien FLAESCH sf at 4js.com
Fri Sep 19 04:41:36 EDT 2008


Hi,

Sorry if I don't follow/understand the details...

But from an ODBC programmer point of view, would it mean that if I want to
use the UTF-8 character set, I will need to convert to UCS-2 and use the W
ODBC functions or can I still use UTF-8 (char*) with the non-W functions?

Cheers,
Seb

James K. Lowden wrote:
> Frediano Ziglio wrote:
>> Il giorno sab, 13/09/2008 alle 16.51 -0400, James K. Lowden ha scritto:
>>> First: What do we mean by "wide"?  UCS-2?  UTF-16?  UCS-4?  UTF-8?  Is
>>> it compile-time dependent?  Run-time?  
>> It depends from DM... unixODBC use UCS-2 while iODBC use wchar_t
>> (usually UCS-4 on Unix.. or not?? I'm not sure, certainly Linux use
>> UCS-4). Using unixODBC there is a configuration flags to use wchar_t but
>> usually is not enabled
> 
> OK, so it's a compile-time setting.  
> 
>>> I see a
>>> reference to a "ODBC 3.5 (or later) Unicode Driver".  Is that what
>>> we're building?  
>> Yes, in a future (not very far) yes
> 
> OK. 
> 
>> Unicode driver means that all ANSI version have a
>> corresponding unicode version (like SQLExecDirectW for SQLExecDirect).
>> The change is interpret characters as wide instead of ANSI.
> 
> I see.  So a Unicode appliction calls SQLExecDirectW, or does a
> preprocessor macro convert it, something like:
> 
> 	#if UNICODE
> 	#define SQLExecDirect SQLExecDirectW
> 	#endif
> 
> ??
> 
>>> Fourth: Can you show me the API function call sequence that mixes
>>> encodings for a single column?  
>> I never tried but I think reading TEXT/NTEXT with SQLGetData changing
>> SQL_C_CHAR/SQL_C_WCHAR for the same column.
> 
> The app can call SQLBindCol in between calls to SQLFetch, too:  
> 
> 	"A column can be bound, unbound, or rebound at any time, even after data
> has been fetched from the result set. The new binding takes effect the
> next time that a function that uses bindings is called."
> (http://msdn.microsoft.com/en-us/library/ms711010(VS.85).aspx)
> 
>>> Maybe it would be easier to create a BRANCH_UNICODE branch in CVS 
>> I would
>> prefer a "from XXX date code is quite broken so if you want to use CVS
>> use cvs co -D XXX". 
> 
> OK.  Maybe just a CVS tag UNICODE_BASE or something like that, so we don't
> have to remember the date.  
> 
> As long as db-lib and ct-lib remain useable in CVS HEAD, I'm happy.  I
> intend to change tds_connect() for example, so broken code would be bad.  
> 
>> To be sure we could branch and continue working on CVS HEAD, having a
>> BRANCH_NOUNICODE. Branch and merging is heavy on CVS, this way main
>> changes will go to the no-branch.
> 
> We can do that later if HEAD becomes too unstable to use.  
> 
>> The problem with "convert nearest the wire" is that at the moment libTDS
>> fetch data and fill row buffer it doesn't know which encode the client
>> wants (SQL_C_CHAR or SQL_C_WCHAR). 
> 
> Understood.  
> 
>> All that stuff suggest me "direct binding"... 
> 
> Right.  Convert at the ODBC<->libtds boundary.  
> 
>> how to implement all new datatypes of mssql2005 and mssql2008 ?? One
>> problem with mssql2005 is the VARCHAR(MAX) which can be very large,
>> something like SYBLONGCHAR/SYBBLOB of Sybase (still not that supported).
> 
> I haven't thought about this very much.  I know that for zero-copy, the
> client library must provide the target buffer into which libtds places the
> data.  
> 
>> I'm currently filling a table of types with flags (like ascii, unicode,
>> fixed and so on) and other informations (varint ms/sybase)
> 
> Excellent.  You might want "cardinal" type, too.  
> 
> Regards, 
> 
> --jkl
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