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| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Pointers as error values |
| Date | 2015-10-20 19:45 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <87io61idk3.fsf@bsb.me.uk> (permalink) |
| References | <bb26d1c2-246b-45cd-8434-583530881c88@googlegroups.com> <n05l9o$cn3$1@speranza.aioe.org> |
Lőrinczy Zsigmond <nospam@for.me> writes: > On 2015.10.19. 9:53, Morten W. Petersen wrote: >> >> I was thinking the other day, that NULL pointers indicate an error. >> That got me wondering, is it possible to use a low number range as >> valid error indicators? > > SIG_IGN comes in my mind: it is tipically (somefunpointer)1 Often it is, yes, but I Morten is, I think, concerned about maximum portability, and what a particular implementation might do is not a good guide for what portable software should do. If you were implementing something like the signal interface in a portable library, your simplest option is to return something of the right type. Thus you might define actual functions call __sig_ign_f__ and __sig_dfl_f__ so that you can #define SIG_IGN __sig_ign_f__ An equivalent idea has already been suggested I think; namely to define specific, static, objects of the right XML structure types so that pointers to them can be returned to indicate some errors. The trouble (also covered I think) is that if you use several there is no simple way to test if a pointer is one of them other than to test all of the for equality. If you use the (xml_element *)3 hack, you can (on many systems) test for the return value being in the error range. But if the object type is a union, you can define a new type for an error object, and create a few of these for the specific errors that you want to signal. Your functions never now return NULL and the test for an error becomes if (ptr->type == XmlError) ... though there is nothing to prevent you (where it makes sense) from making a pointer comparison with one of these objects if (ptr != &Xml_Out_Of_Mem_Error) ... -- Ben.
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Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-19 00:53 -0700
Re: Pointers as error values gazelle@shell.xmission.com (Kenny McCormack) - 2015-10-19 08:26 +0000
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-19 02:27 -0700
Re: Pointers as error values Richard Damon <Richard@Damon-Family.org> - 2015-10-19 23:38 -0400
Re: Pointers as error values jacobnavia <jacob@jacob.remcomp.fr> - 2015-10-19 10:34 +0200
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-19 02:29 -0700
Re: Pointers as error values mark.bluemel@gmail.com - 2015-10-19 05:53 -0700
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-19 10:00 +0000
Re: Pointers as error values Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-19 14:00 +0000
Re: Pointers as error values gwowen <gwowen@gmail.com> - 2015-10-19 08:02 -0700
Re: Pointers as error values James Kuyper <jameskuyper@verizon.net> - 2015-10-19 11:53 -0400
Re: Pointers as error values Ken Brody <kenbrody@spamcop.net> - 2015-10-19 11:25 -0400
Re: Pointers as error values supercat@casperkitty.com - 2015-10-19 08:41 -0700
Re: Pointers as error values Keith Thompson <kst-u@mib.org> - 2015-10-19 08:59 -0700
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-21 07:32 +0200
Re: Pointers as error values Ian Collins <ian-news@hotmail.com> - 2015-10-21 19:17 +1300
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-21 08:31 +0200
Re: Pointers as error values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-21 12:46 +0100
Re: Pointers as error values Robert Wessel <robertwessel2@yahoo.com> - 2015-10-21 09:35 -0500
Re: Pointers as error values Ken Brody <kenbrody@spamcop.net> - 2015-10-21 15:24 -0400
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-22 05:44 +0000
Re: Pointers as error values Keith Thompson <kst-u@mib.org> - 2015-10-21 10:41 -0700
Re: Pointers as error values supercat@casperkitty.com - 2015-10-21 11:28 -0700
Re: Pointers as error values John Temples <usenet@xargs-spam.com> - 2015-10-21 17:45 +0000
Re: Pointers as error values James Kuyper <jameskuyper@verizon.net> - 2015-10-21 14:15 -0400
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-29 16:59 +0100
Re: Pointers as error values supercat@casperkitty.com - 2015-10-29 12:35 -0700
Re: Pointers as error values raltbos@xs4all.nl (Richard Bos) - 2015-10-29 21:45 +0000
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-30 06:09 +0100
Re: Pointers as error values Rosario19 <Ros@invalid.invalid> - 2015-10-30 08:59 +0100
Re: Pointers as error values Rosario19 <Ros@invalid.invalid> - 2015-10-30 09:07 +0100
Re: Pointers as error values Rosario19 <Ros@invalid.invalid> - 2015-10-30 09:38 +0100
Re: Pointers as error values Rosario19 <Ros@invalid.invalid> - 2015-10-30 09:40 +0100
Re: Pointers as error values Robert Wessel <robertwessel2@yahoo.com> - 2015-10-30 04:56 -0500
Re: Pointers as error values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-30 11:00 +0000
Re: Pointers as error values Robert Wessel <robertwessel2@yahoo.com> - 2015-10-29 23:48 -0500
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-30 11:05 +0100
Re: Pointers as error values Richard Damon <Richard@Damon-Family.org> - 2015-10-30 07:45 -0400
Re: Pointers as error values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-30 05:04 -0700
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-30 16:09 +0100
Re: Pointers as error values Keith Thompson <kst-u@mib.org> - 2015-10-30 11:16 -0700
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-30 20:58 +0000
Re: Pointers as error values Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-30 17:12 -0400
Re: Pointers as error values supercat@casperkitty.com - 2015-10-30 14:54 -0700
Re: Pointers as error values Robert Wessel <robertwessel2@yahoo.com> - 2015-10-30 18:48 -0500
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-01 04:00 +0000
Re: Pointers as error values Robert Wessel <robertwessel2@yahoo.com> - 2015-11-01 01:24 -0500
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-31 20:35 +0100
Re: Pointers as error values supercat@casperkitty.com - 2015-10-31 13:33 -0700
Re: Pointers as error values Richard Damon <Richard@Damon-Family.org> - 2015-10-30 22:19 -0400
Re: Pointers as error values supercat@casperkitty.com - 2015-10-30 08:22 -0700
Re: Pointers as error values Geoff <geoff@invalid.invalid> - 2015-10-30 13:11 -0700
Re: Pointers as error values Geoff <geoff@invalid.invalid> - 2015-10-30 13:23 -0700
Re: Pointers as error values Geoff <geoff@invalid.invalid> - 2015-10-21 11:13 -0700
Re: Pointers as error values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-21 20:31 +0100
Re: Pointers as error values Geoff <geoff@invalid.invalid> - 2015-10-22 07:13 -0700
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-26 07:16 +0100
Re: Pointers as error values Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-26 09:37 +0000
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-22 05:38 +0000
Re: Pointers as error values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-22 13:51 +0100
Re: Pointers as error values Keith Thompson <kst-u@mib.org> - 2015-10-22 08:29 -0700
Re: Pointers as error values supercat@casperkitty.com - 2015-10-22 09:21 -0700
Re: Pointers as error values Keith Thompson <kst-u@mib.org> - 2015-10-22 10:52 -0700
Re: Pointers as error values "Morten W. Petersen" <morphex@gmail.com> - 2015-10-26 07:20 +0100
Re: Pointers as error values Keith Thompson <kst-u@mib.org> - 2015-10-26 08:09 -0700
Re: Pointers as error values supercat@casperkitty.com - 2015-10-26 08:40 -0700
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-26 20:02 +0000
Re: Pointers as error values supercat@casperkitty.com - 2015-10-26 13:56 -0700
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-22 21:58 +0000
Re: Pointers as error values James Kuyper <jameskuyper@verizon.net> - 2015-10-22 19:12 -0400
Re: Pointers as error values asetofsymbols@gmail.com - 2015-10-22 18:36 -0700
Re: Pointers as error values asetofsymbols@gmail.com - 2015-10-29 12:47 -0700
Re: Pointers as error values Lőrinczy Zsigmond <nospam@for.me> - 2015-10-20 17:06 +0200
Re: Pointers as error values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-20 19:45 +0100
Re: Pointers as error values supercat@casperkitty.com - 2015-10-20 14:19 -0700
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-21 05:28 +0000
Re: Pointers as error values supercat@casperkitty.com - 2015-10-21 05:48 -0700
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-22 05:52 +0000
Re: Pointers as error values Ken Brody <kenbrody@spamcop.net> - 2015-10-21 15:19 -0400
Re: Pointers as error values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-22 06:06 +0000
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