From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,3a20fa0a5423463c,start X-Google-Attributes: gid103376,public From: gauthier@alphainfo.unilim.fr (Michel Gauthier) Subject: 'is-null' property through file keeping (to gurus) Date: 1997/04/29 Message-ID: #1/1 X-Deja-AN: 238162720 Organization: Universite de Limoges Newsgroups: comp.lang.ada Date: 1997-04-29T00:00:00+00:00 List-Id: This is essentially a question to gurus. To avoid complex generic parameterising, I have made the assumption that the property 'this pointer is null / not null' is invariant when a pointer is written into then read from a file. Another view of the same is 'the null pointer has only one machine implementation and what is kept in a file is no more than a fixed-sized bit sequence'. Can this be a reasonable assumption ? To avoid flames and useless answers, I add that : - I am aware that pointers have no meaning if re-read from a file _written in another execution_ of the program (in fact, formally, they are references to already destroyed objects, hence in principle indistinguishable from null), - the problem occurs _in a low-level layer_ of the programme, but portability is preferable, - what I need is exactly an end-of-sequence boolean information, which can be implemented evenly at a price that is unpleasant so deeply in the programme. So, I'd like to know if there are arguments in favor of or against my assumptions in Ada texts like 'implementation advice' sections, URG work, code-generator documentations, or whatever. ---------- ---------- ---------- ---------- Michel Gauthier / Laboratoire d'informatique 123 avenue Albert Thomas / F-87060 Limoges telephone + 33 5 55 45 73 35 [or ~ 72 32] fax +33 5 55 45 73 15 [or ~72 01] ---------- ---------- ---------- ---------- Si l'an 2000 est pour vous un mysticisme stupide, utilisez la base 9 If you feel year 2000 a stupid mystic craze, use numeration base 9 ---------- ---------- ---------- ----------