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| From | Kaz Kylheku <kaz@kylheku.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: c prog -plz explain |
| Date | 2014-03-11 07:12 +0000 |
| Organization | Aioe.org NNTP Server |
| Message-ID | <20140310235955.176@kylheku.com> (permalink) |
| References | <71fb68ed-69a6-42da-b988-520f9c400ff4@googlegroups.com> <lnvbvlsmm0.fsf@nuthaus.mib.org> <0.09075131e2de08b336cb.20140310232147GMT.87iorly704.fsf@bsb.me.uk> <fb286c5b-c72d-4615-b613-ac1c27f94107@googlegroups.com> |
On 2014-03-11, SAHIL MAHLA <sahilmehla@gmail.com> wrote:
> Yes we are converting a int* to double*.Could you generalize this with a rule
> why that is undefined.
Yes. The rule is written in a document called ISO 9899 ("International
Standard -- Programming Languages -- C").
It was first published in 1990 (ISO 9899:1990) and describes a language called C90.
It was updated to ISO 9899:1999 (C99), and 2011 (C11).
If you read the standard, you will learn about all kinds of rules.
It's really too complicated (and more importantly inefficient) to lecture about
in a series of Usenet articles to complete newbies. Why don't you read the document,
and then if you have questions, then it makes for a better discussion
than "spoon feed me the rules", know what I mean?
The rule which applies here is that an object shall not be accessed through an
lvalue which is not its declared type (or a const/volatile qualified version of
its declared type). An object of type int being accessed as if it were an object
of type double results in undefined behavior.
C is a strongly typed language. It has the concept of type: that an operation
of the correct type must be applied to a datum for well-defined behavior. C has
considerable translation-time type checking in it to support its type system,
but when you use casts, especially for conversions among pointer types, you can
defeat the type system and write programs which break the rules, but do not
produce any diagnostics when compiled, and even make an executable.
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c prog -plz explain SAHIL MAHLA <sahilmehla@gmail.com> - 2014-03-10 14:50 -0700
Re: c prog -plz explain Keith Thompson <kst-u@mib.org> - 2014-03-10 15:41 -0700
Re: c prog -plz explain Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-10 23:21 +0000
Re: c prog -plz explain Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-10 23:24 +0000
Re: c prog -plz explain SAHIL MAHLA <sahilmehla@gmail.com> - 2014-03-10 20:28 -0700
Re: c prog -plz explain James Kuyper <jameskuyper@verizon.net> - 2014-03-11 00:15 -0400
Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 07:12 +0000
Re: c prog -plz explain Noob <root@127.0.0.1> - 2014-03-12 10:43 +0100
Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 14:38 +0000
Re: c prog -plz explain Noob <root@127.0.0.1> - 2014-03-12 15:56 +0100
Re: c prog -plz explain Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-12 11:16 -0400
Re: c prog -plz explain James Kuyper <jameskuyper@verizon.net> - 2014-03-12 11:36 -0400
Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 15:38 +0000
Re: c prog -plz explain glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-12 19:13 +0000
Re: c prog -plz explain Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-12 16:05 -0400
Re: c prog -plz explain James Kuyper <jameskuyper@verizon.net> - 2014-03-12 16:32 -0400
Re: c prog -plz explain Ian Collins <ian-news@hotmail.com> - 2014-03-13 09:38 +1300
Re: c prog -plz explain Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 08:32 -0700
Re: c prog -plz explain glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-12 19:03 +0000
Re: c prog -plz explain James Kuyper <jameskuyper@verizon.net> - 2014-03-12 15:33 -0400
Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 20:56 +0000
Re: c prog -plz explain Ian Collins <ian-news@hotmail.com> - 2014-03-13 10:07 +1300
Re: c prog -plz explain "BartC" <bc@freeuk.com> - 2014-03-11 10:33 +0000
Re: c prog -plz explain Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2014-03-10 18:48 -0400
Re: c prog -plz explain SAHIL MAHLA <sahilmehla@gmail.com> - 2014-03-10 20:26 -0700
Re: c prog -plz explain Ian Collins <ian-news@hotmail.com> - 2014-03-11 16:34 +1300
typecasting (was Re: c prog -plz explain) Jorgen Grahn <grahn+nntp@snipabacken.se> - 2014-03-12 07:03 +0000
Re: typecasting (was Re: c prog -plz explain) Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 07:40 +0000
Re: typecasting (was Re: c prog -plz explain) Lowell Gilbert <lgusenet@be-well.ilk.org> - 2014-03-12 10:47 -0400
Re: typecasting (was Re: c prog -plz explain) Ken Brody <kenbrody@spamcop.net> - 2014-03-12 13:01 -0400
Re: typecasting (was Re: c prog -plz explain) Richard <rgrdev_@gmail.com> - 2014-03-12 12:47 +0100
Re: typecasting (was Re: c prog -plz explain) gazelle@shell.xmission.com (Kenny McCormack) - 2014-03-12 12:39 +0000
Re: typecasting (was Re: c prog -plz explain) Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 15:06 +0000
Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 07:26 +0000
Re: c prog -plz explain Richard <rgrdev_@gmail.com> - 2014-03-11 08:39 +0100
Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 08:08 +0000
Re: c prog -plz explain Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2014-03-11 09:14 -0400
Re: c prog -plz explain Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-11 15:38 +0000
Re: c prog -plz explain Ken Brody <kenbrody@spamcop.net> - 2014-03-11 12:53 -0400
Re: c prog -plz explain Keith Thompson <kst-u@mib.org> - 2014-03-11 11:47 -0700
Re: c prog -plz explain glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-11 21:41 +0000
Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 22:01 +0000
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