[Lazarus] INVALID_* consts

[waldo kitty]

On 6/3/2013 18:54, Hans-Peter Diettrich wrote:
> waldo kitty schrieb:
>> what can we do about INVALID_FILE_SIZE?
>>
>> const
>> INVALID_FILE_SIZE = DWORD($FFFFFFFF);
>>
>> is the above correct? it would seem to be from what i can make out from MSDN
>> and the various C code files i've found it defined in...
>
> Using unsigned constants with int64 filesizes would classify files of exactly
> that size as invalid, while smaller or bigger files would be valid. This
> certainly is *not* what the coder had in mind, so that I'd suggest to inspect
> and fix all occurences of this (and similar) unsigned constants in user code.

i'm (finally) back to trying to poke this conversion thing with a sharp stick... 
i understand what you are saying in the above but i don't know how to "fix all 
occurrences of this (and similar) unsigned constants in user code."... i'm sure 
it is probably something easy that i'm not seeing... something like adding a sign ;)

   eg: INVALID_FILE_SIZE = DWORD(-1);

but how can i know if that will be what OS API functions send back? the above 
const is documented as shown above in the DWORD form so i already know that that 
particular instance from that particular API function will fail... since 
DWORD($FFFFFFFF) <> -1...

>> i kind of have to laugh because on place i read spoke of examples checking the
>> result directly instead of using INVALID_FILE_SIZE and that this was not good
>> coding practice because m$ might change the value of INVALID_FILE_SIZE at any
>> time which would then break all of that code... i makes sense to me O:)
>
> IMO such unsigned constants should be used only in specific cases, e.g. with OS
> defined records containing part of an longer (int64) type. The FCL can use that
> constant in Win32 platform code, the LCL or user code never should use it at all.

i understand this... how can i get this const (as defined) into the FCL if it 
does not already exist? how can i tell my converted delphi project to use the 
FCL in addition to the LCL? right now when i look at the project inspector, the 
LCL is the only "required" package shown...

> I also doubt that the MS documentation is up to date whenever above constant is
> used with anything except struct fields of type DWORD. Even in 32 bit code
> *both* low/high parts of a 64 bit filesize must be checked for
> INVALID_FILE_SIZE, in order to determine a valid result.

the documentation for the above const (which i linked to previously) talks about 
using a different OS API function for those instances where necessary...