[fpc-pascal] QWord/UInt64 and Range Check Errors

Ruediger Hahn ruediger.hahn at itservices-hahn.de
Thu Jun 25 20:52:57 CEST 2009

Jonas Maebe wrote:
> On 25 Jun 2009, at 19:58, Ruediger Hahn wrote:
>> I am just wondering if this is a bug: Can anyone tell me why I get a 
>> "range check error while evaluating constants" with the following 
>> simple program:
>> <code>
>> program Project1;
>> const
>> MyVar : UInt64 = $FFFFFFFFFFFFFFFF; // 4 x 2 Bytes or 4 Words
>> begin
>> end.
>> </code>
> The reason is that $FFFFFFFFFFFFFFFF is parsed as an int64 by FPC. As 
> a result it equals -1, and -1 is not a valid uint64 value.
Ah yes, now I see. In Delphi it is quite the opposite: There I get a 
warning when I try to assign this value to an Int64: "Constant 
expression violates subrange bounds". Unfortunately it took me some 
hours to solve this problem because Lazarus by default has range 
checking enabled (-Cr), so I got an error instead of a warning.

Furthermore IMHO hex values _by_ _default_ should be interpreted as 
positive values. But that might be a matter of taste.

So what do I have to do then? It seems that a cast is the best solution:
  MyConst : UInt64 = UInt64($FFFFFFFFFFFFFFFF);
Am I right?


More information about the fpc-pascal mailing list