Hi *,
I found small incompatibility between Delphi and FPC.

This code:
var a,b: array of byte;
begin
     setlength(a,2);
     b:=copy(a,2,1); //<--HERE "Range check error" in FPC, Delphi
returns empty array
end;

Delphi documentation says:
"If Index is larger than the length of S, *Copy* returns an empty string or array."
http://docwiki.embarcadero.com/VCL/en/System.Copy

Can it be fixed also in FPC?
L.

I think it's a Delphi bug to act like that. You must provide a length that is not bigger in size. It's up to you the developer. Otherwise you might have more then one type of buffer overflows in your code !

The way Delphi solved it, is by taking the responsibility from the developer, and made the code a bit slower.
And as I said, I don't think it's a good idea

It's not a bug in Delphi if they write it in the documentation. Whether we should copy this behavior is the question (maybe only in Delphi mode).

Regards,
Sven

+1 ... @lacak, better fix your code. I don't like to be delphi compatibile with such things.

zeljko

In the mean time there is tons of code that relies on copy() copying until end of string or dynamic array. Constructions like param=copy(s,pos('=')+1,length(s)) are plenty. Just do a grep in the fpc compiler dir for "copy(" and you'l find plenty of copy(s,p+1,255) and the like.

Ludo

29.02.2012 17:05, Sven Barth пишет:

It's not a bug in Delphi if they write it in the documentation. Whether we should copy this behavior is the question (maybe only in Delphi mode).

It cannot be fixed for Delphi mode only because a single copy of RTL is used for all compiler modes. The current situation where out of range 'length' parameter is adjusted but 'index' out of range raises exception is simply self-inconsistent. It is also inconsistent with behavior of Copy for strings. Adjusting index will neither cause any buffer overflows nor make code slower, so it should be fixed.

Regards,
Sergei

Second that, In lack of a explicit "copy-to-end" RTL function I have always used Copy(S, <SomePos>, MaxInt) in Delphi to copy to the end of a string. I find it easier to write, more self-explanatory and perhaps faster to execute (minus a string length fetching and a subtraction) than writing Length(S) - <SomePos>, especially if <SomePos> is an expression.

I forgot that Copy uses a compiler proc instead of being a complete intrinsic. So, yes, you're right ;)

Regards,
Sven

Sergei Gorelkin wrote / napísal(a):

Will you do it or should I register bug in bug tracker? Laco.

29.02.2012 18:21, LacaK пишет:

Please create a Mantis issue, so it won't be forgotten.

Regards,
Sergei

Delphi specified Copy as *not* requiring exact parameters. The length always could be bigger than the string length, in which case the copy stops at the end of the source string. Likewise the starting index can be past the length of the source string, resulting in an empty string.

Performance is not affected, and the overall code size decreases, when the user doesn't have to calculate and check everything, every time before calling Copy. Please understand that even throwing an exception requires an check before, so that it's only a simple decision whether to fix an improper parameter value silently, or to throw an exception.

DoDi

Agreed, please fix it.

Martin

Sergei Gorelkin wrote / napísal(a):

http://bugs.freepascal.org/view.php?id=21396

TIA
-Laco.