Re: [fpc-devel] Compiler hint for uninitialized local variable minor mistake
On 29 May 2009, at 09:04, Micha Nelissen wrote: Jonas Maebe wrote: It is not possible to change this in the compiler. The reason is that if we change the first parameter of fillchar from a "var" parameter (as it is now) into an "out" parameter (so the hint would not be shown), then the behaviour of the code changes. Wasn't "outvar" a long wished feature to solve this? Not that I know. Jonas ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Compiler hint for uninitialized local variable minor mistake
On 29 May 2009, at 09:44, Flávio Etrusco wrote: (...) This is due to the fact that if you pass a variable to an out parameter and this variable is reference counted or contains reference counted elements (in case of an array/record/object), then the compiler has to insert finalization code at the caller side for this variable before passing it in. The result is that if tmp is reference counted but nevertheless somehow contained garbage, e.g. in a program like this: Is Delphi's behavior the same? Yes. Doesn't this have some implications on COM calls? Or is it like this way exactly to make COM work? Indeed. Keep in mind that hints are the lowest level of "programming help" that the compiler has to offer, and it is generally impossible to make your code hint free. They are only intended to help you if you really are at wits end regarding what could be going wrong. Otherwise, it's best to stick to warnings and notes. And this make hints so much less useful... That's the whole point of having a hints category: to put stuff in that we simply cannot guarantee to be useful (but which might be useful under some circumstances). Jonas___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Compiler hint for uninitialized local variable minor mistake
> (...) > > This is due to the fact that if you pass a variable to an out parameter and > this variable is reference counted or contains reference counted elements > (in case of an array/record/object), then the compiler has to insert > finalization code at the caller side for this variable before passing it in. > The result is that if tmp is reference counted but nevertheless somehow > contained garbage, e.g. in a program like this: Is Delphi's behavior the same? I'm not 100% I've read it on any official source, but I never saw it behave differently than "var without the warning". Delphi didn't even have the decency to force/warn one to initialize in the function :-/ Doesn't this have some implications on COM calls? Or is it like this way exactly to make COM work? > > Keep in mind that hints are the lowest level of "programming help" that the > compiler has to offer, and it is generally impossible to make your code hint > free. They are only intended to help you if you really are at wits end > regarding what could be going wrong. Otherwise, it's best to stick to > warnings and notes. > And this make hints so much less useful... Best regards, Flávio ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Compiler hint for uninitialized local variable minor mistake
Jonas Maebe wrote: It is not possible to change this in the compiler. The reason is that if we change the first parameter of fillchar from a "var" parameter (as it is now) into an "out" parameter (so the hint would not be shown), then the behaviour of the code changes. Wasn't "outvar" a long wished feature to solve this? Micha ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Compiler hint for uninitialized local variable minor mistake
On 29 May 2009, at 01:44, ABorka wrote: fillchar(tmp, sizeof(tmp), #0); gives the Hint: Local variable "tmp" does not seem to be initialized message upon compilation, which should not happen because it is actually the initialization. It is not possible to change this in the compiler. The reason is that if we change the first parameter of fillchar from a "var" parameter (as it is now) into an "out" parameter (so the hint would not be shown), then the behaviour of the code changes. This is due to the fact that if you pass a variable to an out parameter and this variable is reference counted or contains reference counted elements (in case of an array/record/object), then the compiler has to insert finalization code at the caller side for this variable before passing it in. The result is that if tmp is reference counted but nevertheless somehow contained garbage, e.g. in a program like this: type pr = ^tr; tr = record a: ansistring; end; var p : pr; begin p:=myspecialgetmem(sizeof(tr)); fillchar(p^,sizeof(p^),0); end; then the program will try to finalize the garbage at run time and most likely crash. This may seem far fetched, but this sort of stuff happens in real code (I got crashes before I knew this and tried to change the move() procedure in this way). Keep in mind that hints are the lowest level of "programming help" that the compiler has to offer, and it is generally impossible to make your code hint free. They are only intended to help you if you really are at wits end regarding what could be going wrong. Otherwise, it's best to stick to warnings and notes. Jonas ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
[fpc-devel] Compiler hint for uninitialized local variable minor mistake
fillchar(tmp, sizeof(tmp), #0); gives the Hint: Local variable "tmp" does not seem to be initialized message upon compilation, which should not happen because it is actually the initialization. ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
