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Re: arm-gcc: pointer to constant string

From Stefan Reuther <stefan.news@arcor.de>
Newsgroups comp.arch.embedded
Subject Re: arm-gcc: pointer to constant string
Date 2018-09-15 18:32 +0200
Message-ID <pnjj84.4c8.1@stefan.msgid.phost.de> (permalink)
References <pnfp7q$a7b$1@dont-email.me> <g01ee7F9ruuU1@mid.individual.net> <png2d4$opd$1@dont-email.me> <pnh3s7.12k.1@stefan.msgid.phost.de> <pnh09a$ou3$1@dont-email.me>

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Am 14.09.2018 um 20:56 schrieb David Brown:
> On 14/09/18 19:57, Stefan Reuther wrote:
>> Am 14.09.2018 um 12:26 schrieb David Brown:
>>> No, it is not - not for decades.  In C, "string" is defined in 7.1.1 of
>>> the current standard as "A string is a contiguous sequence of characters
>>> terminated by and including the first null character."
>>
>> That is the library definition of "string". The language definition of a
>> string literal is in §6.4.5 which says:
>>
>> # In translation phase 7, a byte or code of value zero is appended to
>> # each multibyte character sequence that results from a string literal
>> # or literals. The multibyte character sequence is then used to
>> # initialize an array of static storage duration and length just
>> # sufficient to contain the sequence. [...]
>>
>> (paragraph 5 in ISO 9899:1999, paragraph 6 in n1548)
> 
> Yes, I know the difference between a string and a string literal - I
> said that in a bit you snipped.
> 
> And the library definition of a "string" /is/ the C definition of
> "string".  The term is italicised in 7.1.1, denoting that it is defined
> in that paragraph.

The library makes no mention of storage classes, meaning: it does not
care about storage classes.

The language defines what happens with a string literal in §6.4.5p5/6,
namely: construction of an array of static storage duration, with
content that - lo and behold - fulfils the library's requirements of a
string, by being a zero-terminated array of characters.

> I know that's what the OP's code needs in order to be correct - the
> question is if the C standards guarantee that his code does what he wants.

The question was: is a string literal's address and content valid after
the function containing it exits? The answer is: yes.

>> TL;DR: OP's code is safe, language-wise.
> 
> Can you back that up with references to the standard?

See above.


  Stefan

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Thread

arm-gcc: pointer to constant string pozz <pozzugno@gmail.com> - 2018-09-14 09:50 +0200
  Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-14 11:18 +0200
    Re: arm-gcc: pointer to constant string pozz <pozzugno@gmail.com> - 2018-09-14 13:05 +0200
      Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-14 13:25 +0200
  Re: arm-gcc: pointer to constant string Nils M Holm <nmh@ananda.local> - 2018-09-14 09:47 +0000
    Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-14 12:26 +0200
      Re: arm-gcc: pointer to constant string Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2018-09-14 14:52 +0200
        Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-14 16:04 +0200
          Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-14 15:48 +0100
            Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-14 17:02 +0200
              Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-14 18:45 +0100
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-14 20:37 +0200
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-14 20:51 +0100
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-15 16:24 +0200
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-15 17:28 +0100
                Re: arm-gcc: pointer to constant string Clifford Heath <no.spam@please.net> - 2018-09-16 13:58 +1000
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-16 08:42 +0100
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-16 08:47 +0100
                Re: arm-gcc: pointer to constant string Clifford Heath <no.spam@please.net> - 2018-09-16 20:18 +1000
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-16 12:25 +0100
                Re: arm-gcc: pointer to constant string Clifford Heath <no.spam@please.net> - 2018-09-16 22:22 +1000
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-16 15:00 +0200
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-16 14:33 +0100
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-16 22:06 +0200
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-16 21:42 +0100
                Re: arm-gcc: pointer to constant string Les Cargill <lcargill99@comcast.com> - 2018-09-17 21:24 -0500
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-18 08:49 +0200
                Re: arm-gcc: pointer to constant string Les Cargill <lcargill99@comcast.com> - 2018-09-21 22:15 -0500
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-22 11:53 +0200
                Testing (Was: arm-gcc: pointer to constant string) Jacob Sparre Andersen <jacob@jacob-sparre.dk> - 2018-09-22 12:16 +0200
                Re: Testing (Was: arm-gcc: pointer to constant string) David Brown <david.brown@hesbynett.no> - 2018-09-22 13:31 +0200
                Re: Testing (Was: arm-gcc: pointer to constant string) Clifford Heath <no.spam@please.net> - 2018-09-23 09:26 +1000
                Re: arm-gcc: pointer to constant string Niklas Holsti <niklas.holsti@tidorum.invalid> - 2018-09-22 20:06 +0300
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-23 14:39 +0200
                Re: arm-gcc: pointer to constant string Les Cargill <lcargill99@comcast.com> - 2018-09-22 13:50 -0500
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-23 15:21 +0200
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-23 16:06 +0100
                Re: arm-gcc: pointer to constant string julio@diegidio.name - 2018-09-23 08:41 -0700
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-23 16:49 +0100
                Re: arm-gcc: pointer to constant string julio@diegidio.name - 2018-09-23 08:56 -0700
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-23 18:20 +0100
                Re: arm-gcc: pointer to constant string julio@diegidio.name - 2018-09-23 12:05 -0700
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-23 20:50 +0100
                Re: arm-gcc: pointer to constant string Les Cargill <lcargill99@comcast.com> - 2018-09-23 12:04 -0500
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-23 18:27 +0100
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-23 19:37 +0200
                Re: arm-gcc: pointer to constant string Jacob Sparre Andersen <jacob@jacob-sparre.dk> - 2018-09-24 12:53 +0200
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-24 13:49 +0200
                Re: arm-gcc: pointer to constant string Les Cargill <lcargill99@comcast.com> - 2018-09-28 20:17 -0500
                Re: arm-gcc: pointer to constant string Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-09-18 08:32 +0100
                Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-18 10:02 +0200
                Re: arm-gcc: pointer to constant string Les Cargill <lcargill99@comcast.com> - 2018-09-21 22:17 -0500
          Re: arm-gcc: pointer to constant string Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2018-09-14 18:30 +0200
            Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-14 20:46 +0200
      Re: arm-gcc: pointer to constant string Stefan Reuther <stefan.news@arcor.de> - 2018-09-14 19:57 +0200
        Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-14 20:56 +0200
          Re: arm-gcc: pointer to constant string Stefan Reuther <stefan.news@arcor.de> - 2018-09-15 18:32 +0200
            Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-16 15:06 +0200
      Re: arm-gcc: pointer to constant string Richard Damon <Richard@Damon-Family.org> - 2018-09-14 19:59 -0400
        Re: arm-gcc: pointer to constant string David Brown <david.brown@hesbynett.no> - 2018-09-15 16:25 +0200
  Re: arm-gcc: pointer to constant string Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-09-14 13:49 +0300

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