Hairy Pixels via fpc-pascal said on Wed, 7 Jun 2023 15:44:43 +0700
>I'm curious, why doesn't the following code give a warning? Shouldn't
>the compiler know you're assigning to "r" which hasn't been
>initialized yet?
>
>type
> TMyClass = class
> x: integer;
> end;
>
>procedure MyProcedure;
>var
> r: TMyClass;
>begin
> r.x := 1;
>end;
>
>
>Regards,
> Ryan Joseph
If I had to guess, I'd say it's because you needed to and did declare
{$mode objfpc} or {$mode delphi}, which, my guess would be, don't warn
against using uninitialized variables. The following program contains
your code but includes r := tmyclass.create to allocate RAM to the
object. If that line is commented out, you get a runtime 216, which I
believe is a memory access violation.
================================================
{$mode objfpc} {Needed for classes}
{$rangechecks on} {Check for runtime memory tromp}
{$warnings on} {List all warnings}
program junk3;
type
TMyClass = class
x: integer;
end;
procedure show(c: tmyclass);
begin
writeln(c.x);
end;
procedure MyProcedure;
var
r: TMyClass;
begin
{Comment out following line to produce memory error}
r := tmyclass.create; {Allocate ram for object r}
r.x := 1;
show(r);
end;
begin
myprocedure;
writeln('Finished');
end.
================================================
I explored {$warn whatever}, and none of the whatevers pertained to
uninitialized varibles, and {$warnings on} didn't bring out a warning.
I've seen uninitialized var warnings in other code, so by process of
elimination I'd imagine this is due to {$mode delphi} and its cousins,
which are necessary to recognize "class" as a reserved word.
I know this isn't a very satisfying answer, but it's the best I can
come up with.
SteveT
Steve Litt
Autumn 2022 featured book: Thriving in Tough Times
http://www.troubleshooters.com/bookstore/thrive.htm
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
