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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: sprintf and the trailing null |
| Date | 2015-07-06 10:46 -0700 |
| Organization | None to speak of |
| Message-ID | <lnmvz9uqk3.fsf@kst-u.example.com> (permalink) |
| References | (3 earlier) <mne1fl$dm7$1@dont-email.me> <8ee8235d-f52a-4e2c-94b5-11d7b86cbc60@googlegroups.com> <mne4af$q93$1@dont-email.me> <lnvbdxuxz2.fsf@kst-u.example.com> <mneb3m$n6e$1@dont-email.me> |
Bartc <bc@freeuk.com> writes:
> On 06/07/2015 16:06, Keith Thompson wrote:
>> Bartc <bc@freeuk.com> writes:
>> [...]
>>> If you do know the length of the result, as in the above example, then
>>> snprintf() will not append the nul, if the buffer provided is exactly
>>> the write size.
>>
>> That's incorrect; snprintf always writes a terminating null
>> character to the target array (unless n==0 and it doesn't write
>> anything at all). It will truncate the output if necesesary to leave
>> room for the '\0'. N1570 7.21.6.5p2:
>>
>> The snprintf function is equivalent to fprintf, except that
>> the output is written into an array (specified by argument s)
>> rather than to a stream. If n is zero, nothing is written, and
>> s may be a null pointer. Otherwise, output characters beyond
>> the n-1st are discarded rather than being written to the array,
>> and a null character is written at the end of the characters
>> actually written into the array. If copying takes place between
>> objects that overlap, the behavior is undefined.
>>
>
> MS' doc say otherwise:
> -----------------------
> Let len be the length of the formatted data string, not including the
> terminating null. len and count are in bytes for _snprintf, wide
> characters for _snwprintf.
The document you're quoting is for something called _snprintf, which is
a distinct function, with a different name, from the standard snprintf.
(snprintf was added to C by the 1999 standard. I think Microsoft
invented its own non-standard version before that.)
[...]
> But most C compilers behave as you suggest. I was hoping to be able to
> run MSVC in the form of CL.EXE (/this/ is the sort of reason I wanted it
> around, but it's not worth 6-11GB of disk space!), but it failed trying
> to link in snprintf(). And I've no idea how to fix it.
*All* C implementations (for C99 or later) behave like that. Any that
don't are not C implementations.
> I think Rick uses MSVC and that might have been a (non-portable)
> solution if it behaved as its docs say.
>
> However, TCC (Tiny C Compiler) appears to behave like MS says it does.
> The following program prints 49 50 0 99... on most compilers, but 49 50
> 51 99 ... with TCC:
>
> #include <stdio.h>
>
> int main(void) {
> char str[]={99,99,99,99,99,99,99,99};
> int i;
>
> snprintf(str,3,"%3d",12345);
>
> for (i=0; i<sizeof(str); ++i)
> printf("%d ",str[i]);
> }
If so, then tcc is non-conforming. But I just tried it with tcc version
0.9.25 on Linux Mint, and it behaves correctly.
As far as I can tell, tcc uses the system's C library. snprintf is
implemented by the library, not by the compiler. It may be that tcc is
using a non-conforming C library on your system.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 06:16 -0700
Re: sprintf and the trailing null John McCue <jmccue@jmcnet1.bstnma.east.verizon.net> - 2015-07-06 13:30 +0000
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 06:37 -0700
Re: sprintf and the trailing null Reinhardt Behm <rbehm@hushmail.com> - 2015-07-06 21:58 +0800
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 07:12 -0700
Re: sprintf and the trailing null Reinhardt Behm <rbehm@hushmail.com> - 2015-07-06 22:34 +0800
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 08:44 -0700
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-06 15:46 +0100
Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-06 08:06 -0700
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-06 17:42 +0100
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 09:48 -0700
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-06 18:07 +0100
Re: sprintf and the trailing null Martin Shobe <martin.shobe@yahoo.com> - 2015-07-06 12:40 -0500
Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-06 10:46 -0700
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-06 18:58 +0100
Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-06 16:38 +0100
Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-06 23:44 +0100
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 15:48 -0700
Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-08 20:09 +0300
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-08 10:11 -0700
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-08 19:01 +0100
Re: sprintf and the trailing null David Kleinecke <dkleinecke@gmail.com> - 2015-07-09 09:02 -0700
Re: sprintf and the trailing null Richard Heathfield <rjh@cpax.org.uk> - 2015-07-09 17:07 +0100
Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-10 17:06 +0300
Re: sprintf and the trailing null glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-09 17:42 +0000
Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-10 13:33 +0300
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-10 12:09 +0100
Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-10 04:51 -0700
Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-10 17:24 +0100
Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-10 08:33 -0700
Re: sprintf and the trailing null Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-11 04:58 -0700
Re: sprintf and the trailing null jt@toerring.de (Jens Thoms Toerring) - 2015-07-06 14:15 +0000
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 07:20 -0700
Re: sprintf and the trailing null raltbos@xs4all.nl (Richard Bos) - 2015-07-06 19:54 +0000
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 13:31 -0700
Re: sprintf and the trailing null Richard Heathfield <rjh@cpax.org.uk> - 2015-07-06 21:52 +0100
Re: sprintf and the trailing null raltbos@xs4all.nl (Richard Bos) - 2015-07-06 22:52 +0000
Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-07 01:04 +0100
Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-06 19:13 -0700
Re: sprintf and the trailing null Reinhardt Behm <rbehm@hushmail.com> - 2015-07-07 12:45 +0800
Re: sprintf and the trailing null Rosario19 <Ros@invalid.invalid> - 2015-07-07 10:15 +0200
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-07 10:31 +0100
Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-07 02:51 -0700
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-07 12:10 +0100
Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-07 05:08 -0700
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-07 13:52 +0100
Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-08 20:20 +0300
Re: sprintf and the trailing null Bartc <bc@freeuk.com> - 2015-07-08 18:51 +0100
Re: sprintf and the trailing null raltbos@xs4all.nl (Richard Bos) - 2015-07-09 10:27 +0000
Re: sprintf and the trailing null Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-10 19:03 -0700
Re: sprintf and the trailing null gordonb.7tw58@burditt.org (Gordon Burditt) - 2015-07-07 15:40 -0500
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-07 15:14 -0700
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 07:27 -0700
Re: sprintf and the trailing null jt@toerring.de (Jens Thoms Toerring) - 2015-07-06 16:46 +0000
Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-06 07:56 -0700
Re: sprintf and the trailing null Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-07-06 09:32 -0600
Re: sprintf and the trailing null Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-06 08:37 -0700
Re: sprintf and the trailing null Keith Thompson <kst-u@mib.org> - 2015-07-06 08:54 -0700
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 08:53 -0700
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 09:00 -0700
Re: sprintf and the trailing null Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-06 17:14 +0100
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 09:24 -0700
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 09:31 -0700
Re: sprintf and the trailing null Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> - 2015-07-07 01:43 +0200
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 17:09 -0700
Re: sprintf and the trailing null Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-07-06 21:08 -0600
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-06 21:29 -0700
Re: sprintf and the trailing null Phil Carmody <pc+usenet@asdf.org> - 2015-07-08 20:24 +0300
Re: sprintf and the trailing null "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-08 10:44 -0700
Re: sprintf and the trailing null Les Cargill <lcargill99@comcast.com> - 2015-07-07 21:48 -0500
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