[fpc-devel]Format() incompatibility with Delphi

[Michalis Kamburelis]

Hi

What should
   Format('%d %d %0:d %d', [0, 1, 2, 3])
return ? Delphi help is clear about that : "Setting the index specifier 
affects all subsequent formatting", so it should return '0 1 0 1' (and 
it does when compiled with Delphi).

FPC help is not clear about that. And unfortunately it turns out that 
Format() implemented in FPC's SysUtils does not behave like in Delphi: 
Format() call mentioned above returns '0 1 0 2' when compiled with FPC 
(so it is like "Setting the index specifier _does not_ affect subsequent 
formatting").

To fix this (i.e., make it Delphi-compatible) you have to change in file 
sysstr.inc in function Checkarg at line 862 (as of latest FPC version 
from CVS) from
   if Index=-1 then
     begin
     DoArg:=Argpos;
     inc(ArgPos);
     end
   else
     DoArg:=Index;
to
   if Index=-1 then
     DoArg:=Argpos else
     DoArg:=Index;
   ArgPos:=DoArg+1;

This fix may broke existing code (that depends on the way how Format() 
in FPC works) but I guess that such code may be considered buggy anyway 
since FPC documentation was not clear about whether setting index 
specifier affects subsequent formatting or not. Besides, if you want to 
make Format() fully Delphi-compatible, there is no other way to fix 
this, you have to change it's present behaviour.

BTW, I would also advice adding some notes about that to the FPC 
SysUtils.Format documentation.

Regards,
Michalis Kamburelis <michalis at camelot.homedns.org>