Jeff Hobbs wrote:

>  In looking into the best solution for 2790615
>  https://sourceforge.net/tracker/?func=detail&atid=112997&aid=2790615&group_id
>  =12997
>  Don noted that Tcl_ObjPrintf (added in 8.5) or Tcl_AppendFormatToObj
>  would be good alternatives to the coding changes I was using.
> 
>  This would change, eg tkEntry.c:EntryUpdateScrollbar from (partial):
>  [ ... Tcl_PrintDouble ... ]
>  to:
>       EntryVisibleRange(entryPtr, &first, &last);
>       objPtr = Tcl_ObjPrintf("%s %f %f", entryPtr->scrollCmd, first, last);
>       Tcl_IncrRefCount(objPtr);
>       code = Tcl_EvalObjEx(interp, objPtr, TCL_EVAL_GLOBAL|TCL_EVAL_DIRECT);
>  ...


See also #2112563:

<URL: http://sourceforge.net/tracker/index.php?func=detail&aid=2112563&group_id=12997&atid=1
12997 > 


>  the problem is that Tcl_PrintDouble takes into account the (now
>  deprecated) tcl_precision variable.  The above causes errors in the test
>  suite for where "scrollCmd 0.0 1.0" was expected, it now receives
>  "scrollCmd 0.000000 1.000000".  These are error cases that have exact
>  expectations on the string output.

The format should be "%s %g %g" instead of "%s %f %f".
That's what Tk used to use -- but see also #2112563.

>  Most uses of the ~25 Tcl_PrintDoubles in Tk relate to scrolling, and
>  that the values passed are moved through Tcl_PD, whereas the above goes
>  to the raw sprintf handling of %f.

The problem with *that* is, if a buggy extension (or buggy
Windows printer driver, or buggy embedder...) calls setlocale(),
then sprintf(... "%g" ...); can -- depending on LC_NUMERIC --
produce output that can't be reparsed by Tcl as a floating point number.

The ::tcl_precision-induced breakage is a less severe problem --
in fact, it's not really even breakage, it only affects code
(like the test suite) that compares numbers as strings instead
of as numbers.  And there is a simple fix for any applications
that might be affected by this: stop setting ::tcl_precision,
and stop comparing numbers as strings.

The setlocale()-induced breakage is much harder to work around.
For one, it _completely_ breaks the application -- scrollbars
simply stop working.  And although calling setlocale() is also
a "Don't Do That" situation, applications don't always have
as much control over that.  (Buggy Windows printer drivers
have been known to cause this problem a couple times in the past.)



--Joe English

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