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From: jos@cs.vu.nl (Jos Warmer)
Newsgroups: comp.lang.eiffel
Subject: Bug in array.resize
Message-ID: <5984@star.cs.vu.nl>
Date: 15 Mar 90 09:17:40 GMT
Sender: news@cs.vu.nl
Organization: Fac. Wiskunde & Informatica, VU, Amsterdam
Lines: 51

The resize routine is incorrect for zero sized arrays:

class FORCE

feature
    s : ARRAY[STRING];

    Create is
    do
	s.Create(1, 0);
	s.force("twelve", 12);
    end;
end;

Ruinning gives:

System execution failed.
Below is the sequence of recorded exceptions:
--------------------------------------------------------------------------------
Object Class        Routine              Nature of exception              Effect
--------------------------------------------------------------------------------
6C540  ARRAY        resize               External event:
					 Segmentation fault.              Fail
--------------------------------------------------------------------------------
6C540  ARRAY        force                External event:
				         Segmentation fault.              Fail
--------------------------------------------------------------------------------
6CAFC  FORCE        create               External event:
				         Segmentation fault.              Fail
--------------------------------------------------------------------------------

The problem is identified as follows:

	In array.resize the C function `arycpy' is called.
	This function is defined in the file `_basic.c'.
	It calls the macro `gentest' with first argument `oldarea'
	(which is the `area' from class array).
	This macro tries to get the `info' field of area.
	Beacuse the array is empty, area was never assigned to,
	so this means dereferencing a null pointer.
	Ergo: segmentation fault.

			Jos Warmer
			jos@cs.vu.nl

PS: I sometimes get the same execution failure with non-zerosized arrays.
    But I cannot reproduce them in a small example.
--
                                 Jos Warmer
				 jos@cs.vu.nl
				 ...uunet!mcvax!cs.vu.nl!jos