Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.c > #140337
| From | "Pascal J. Bourguignon" <pjb@informatimago.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Distributing C as headers. |
| Date | 2019-01-28 01:19 +0100 |
| Organization | Informatimago |
| Message-ID | <m27eepeire.fsf@despina.home> (permalink) |
| References | (11 earlier) <ln8sz7yrq4.fsf@kst-u.example.com> <m2imybdp04.fsf@despina.home> <q2l6r5$suk$1@dont-email.me> <m2bm41ek17.fsf@despina.home> <%Hr3E.90867$nC1.33629@fx04.am4> |
Bart <bc@freeuk.com> writes:
> On 27/01/2019 23:51, Pascal J. Bourguignon wrote:
>> James Kuyper <jameskuyper@alumni.caltech.edu> writes:
>
>>> Let's break this down into pieces, so I can have some idea what it is
>>> you're claiming. Do you believe that it's impossible to write Pascal
>>> code that can crash? I know that's not what you said, but I want to
>>> cover all the possibilities.
>>
>> compare:
>>
>> void strcpy(char* dst,const char* src);
>>
>> with:
>>
>> procedure string_copy(var dst:string;src:string);
>>
>>
>> In C, you need a lot more information to be able to use the header.
>> In Pascal, you have all the information you need:
>>
>> var
>> dst:string;
>> begin
>> string_copy(dst,'Hello World');
>> end;
>>
>> will work without crashing.
>
> What would string_copy(dst, dst) do? What is the capacity of dst?
> (Last time I used Pascal, strings had to have a fixed length.)
That's the point: dst is not even allocated or initialised before
calling the function! it's a var parameter! It's string_copy that will
allocate it.
>> strcpy specifies pointers to a single char. We need to know what this
>> means. For example, that dst must be pointing to a block of memory of
>> size greater than strlen(src)+1.
>
> Yes, C is a lower level language.
>
> It's quite possible the implementation of your Pascal fragment will
> end up calling memcpy() to do the actual copying, which has the same
> issues as strcpy().
>
> Yet it won't crash; why not?
Good question. It won't crash because the constraints required to use
the low-level functions will be fulfilled by debugged primitive library
code, instead of the application programmer.
A lot of C functions take a pointer and a size (or a length; Hello
off-by-one errors!).
Instead they should take an object abstracting away those elements, so
that their consistency can be ensured by the functional abstraction.
strncpy(dst,src,size); /* crash ensured */
string_copy(dst,src); /* no crash possible, because string_copy
with handle all the cases, given
src->characters, src->length and
dst->characters, dst->allocated_size */
> These were the kinds of restrictions which made it hard to use Pascal
> for anything serious.
LOL
> You write a program to generate some machine code in a
> byte-array. Then you want to execute that code; how do you do it?
> (Ignore read-write-execute permissions; just to jump to it and
> return.)
You use a safe API defined to do it safely.
>> Note that you could define an abstract data type in C, and use it; then
>> the header declarations could be more self-contained.
>
> It is possible to write in a subset of C and avoid superfluous macros
> and typedefs to end up with clean-looking, readable and informative
> headers. But people don't always do that. (A lot of the time they are
> just masses of #ifs and #ifdefs and endless macros.)
Yep.
--
__Pascal J. Bourguignon__
http://www.informatimago.com
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Distributing C as headers. Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-01-25 07:23 -0800
Re: Distributing C as headers. Thiago Adams <thiago.adams@gmail.com> - 2019-01-25 07:31 -0800
Re: Distributing C as headers. Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-01-25 07:33 -0800
Re: Distributing C as headers. Mateusz Viste <mateusz@wont.tell> - 2019-01-25 15:42 +0000
Re: Distributing C as headers. gazelle@shell.xmission.com (Kenny McCormack) - 2019-01-25 17:40 +0000
Re: Distributing C as headers. Thiago Adams <thiago.adams@gmail.com> - 2019-01-25 09:59 -0800
Re: Distributing C as headers. Thiago Adams <thiago.adams@gmail.com> - 2019-01-25 10:01 -0800
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-25 22:17 +0100
Re: Distributing C as headers. Bart <bc@freeuk.com> - 2019-01-25 21:33 +0000
Re: Distributing C as headers. Mateusz Viste <mateusz@wont.tell> - 2019-01-25 18:07 +0000
Re: Distributing C as headers. gazelle@shell.xmission.com (Kenny McCormack) - 2019-01-25 18:46 +0000
Re: Distributing C as headers. Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-01-25 19:43 -0700
Re: Distributing C as headers. Mateusz Viste <mateusz@wont.tell> - 2019-01-26 08:13 +0000
Re: Distributing C as headers. Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-01-26 13:39 -0700
Re: Distributing C as headers. Mateusz Viste <mateusz@wont.tell> - 2019-01-26 21:00 +0000
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-26 22:29 +0100
Re: Distributing C as headers. nobody@example.org (Scott) - 2019-01-27 04:56 +0000
Re: Distributing C as headers. Dan Purgert <dan@djph.net> - 2019-01-27 11:36 +0000
Re: Distributing C as headers. Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-02-25 12:26 -0800
Re: Distributing C as headers. "Jason C. McDonald" <indeliblebluepen@gmail.com> - 2019-02-28 19:52 +0000
Re: Distributing C as headers. Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2019-02-28 15:04 -0500
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-02-28 21:40 +0100
Re: Distributing C as headers. James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-02-28 13:57 -0800
Re: Distributing C as headers. Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-01-27 13:33 +0000
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-27 15:06 +0100
Re: Distributing C as headers. luser droog <luser.droog@gmail.com> - 2019-01-26 13:01 -0800
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-26 22:30 +0100
Re: Distributing C as headers. Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-02-02 09:27 +0000
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-26 22:23 +0100
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-26 13:39 -0800
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-26 22:47 +0100
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-26 14:33 -0800
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-26 23:37 +0100
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-26 15:09 -0800
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-27 15:11 +0100
Re: Distributing C as headers. James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-01-27 16:12 -0500
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-28 00:51 +0100
Re: Distributing C as headers. Bart <bc@freeuk.com> - 2019-01-28 00:06 +0000
Re: Distributing C as headers. Bart <bc@freeuk.com> - 2019-01-28 00:18 +0000
Re: Distributing C as headers. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-01-28 01:12 +0000
Re: Distributing C as headers. Bart <bc@freeuk.com> - 2019-01-28 01:35 +0000
Re: Distributing C as headers. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-01-28 02:19 +0000
Re: Distributing C as headers. Bart <bc@freeuk.com> - 2019-01-28 10:40 +0000
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-28 12:22 +0100
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-28 12:21 +0100
Re: Distributing C as headers. Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-01-28 04:03 -0800
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-28 13:23 +0100
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-28 11:16 -0800
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-28 21:08 +0100
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-28 01:19 +0100
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-27 16:59 -0800
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-27 16:33 -0800
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-28 01:35 +0100
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-27 17:20 -0800
Re: Distributing C as headers. James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-01-27 22:50 -0500
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-28 06:52 +0100
Re: Distributing C as headers. Bart <bc@freeuk.com> - 2019-01-28 10:55 +0000
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-28 12:26 +0100
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-28 13:27 +0100
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-28 13:26 +0100
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-28 14:03 +0100
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-28 11:12 -0800
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-28 12:25 +0100
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-28 13:33 +0100
Re: Distributing C as headers. Keith Thompson <kst-u@mib.org> - 2019-01-28 11:20 -0800
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-28 21:11 +0100
Re: Distributing C as headers. scott@slp53.sl.home (Scott Lurndal) - 2019-01-28 21:12 +0000
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-28 23:06 +0100
Re: Distributing C as headers. David Brown <david.brown@hesbynett.no> - 2019-01-27 15:02 +0100
Re: Distributing C as headers. "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-25 17:51 +0100
Re: Distributing C as headers. fir <profesor.fir@gmail.com> - 2019-01-25 14:28 -0800
csiph-web