Re: "undefined behavior"?

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Sujet : Re: "undefined behavior"?
De : Keith.S.Thompson+u (at) *nospam* gmail.com (Keith Thompson)
Groupes : comp.lang.c
Date : 14. Jun 2024, 22:43:28
Autres entêtes
Organisation : None to speak of
Message-ID : <87zfrn45n3.fsf@nosuchdomain.example.com>
References : 1 2 3 4 5 6 7 8 9 10
User-Agent : Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux)
Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
[...]
I don't know.  The default gcc on my system diagnoses it by default, but
various versions of gcc I've built from source do not.  Perhaps Ubuntu
configures gcc differently.  (Ubuntu 22.04.4, gcc 11.4.0.)  I'm building
gcc 11.4.0 from source, and I'll compare its behavior to that of
Ubuntu's gcc 11.4.0-1ubuntu1~22.04.
[...]

Context: Warning about incorrect printf format strings, such as
`printf("%d\n", strlen(s));` ("%d" requires an int argument but strlen()
returns a result of type size_t).

I've confirmed that, on my Ubuntu 22.04 system, the system-provided
gcc ("Ubuntu 11.4.0-1ubuntu1~22.04") warns about the mismatch, but
gcc 11.4.0 built from source does not.

So Ubuntu (or its upstream Debian) does a custom build of gcc that
enables "-Wformat" by default.

Confirmed by this answer on Stack Overflow:
<https://stackoverflow.com/a/50112401/827263>
"""
This is not caused by a difference in GCC versions. Rather, Ubuntu has
modified GCC to enable -Wformat -Wformat-security by default. If you
pass those options on Arch Linux, you should see the same behaviour
there.
"""

(The answer contains a link to a web page that no longer exists.)

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */

Date Sujet#  Auteur
12 Jun 24 * "undefined behavior"?77DFS
12 Jun 24 +* Re: "undefined behavior"?39Barry Schwarz
12 Jun 24 i`* Re: "undefined behavior"?38DFS
13 Jun 24 i `* Re: "undefined behavior"?37Keith Thompson
13 Jun 24 i  `* Re: "undefined behavior"?36DFS
13 Jun 24 i   `* Re: "undefined behavior"?35Keith Thompson
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13 Jun 24 i     i+* Re: "undefined behavior"?22Malcolm McLean
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14 Jun 24 i     ii   i`* Re: "undefined behavior"?8Ben Bacarisse
15 Jun 24 i     ii   i `* Re: "undefined behavior"?7Malcolm McLean
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16 Jun 24 i     ii   i    `* Re: "undefined behavior"?2David Brown
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14 Jun 24 i     ii    `* Re: "undefined behavior"?2Ben Bacarisse
15 Jun 24 i     ii     `- Re: "undefined behavior"?1Chris M. Thomasson
14 Jun 24 i     i`* Re: "undefined behavior"?6Keith Thompson
14 Jun 24 i     i +- Re: "undefined behavior"?1bart
14 Jun 24 i     i +* Re: "undefined behavior"?3David Brown
14 Jun 24 i     i i`* Re: "undefined behavior"?2Keith Thompson
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14 Jun 24 i     i `- Re: "undefined behavior"?1Keith Thompson
13 Jun 24 i     `* Re: "undefined behavior"?3Keith Thompson
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14 Jun 24 i       `- Re: "undefined behavior"?1Keith Thompson
12 Jun 24 +* Re: "undefined behavior"?15David Brown
13 Jun 24 i+* Re: "undefined behavior"?6Keith Thompson
13 Jun 24 ii+* Re: "undefined behavior"?2David Brown
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14 Jun 24 i   `- Re: "undefined behavior"?1David Brown
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13 Jun 24 i +* Re: "undefined behavior"?2Janis Papanagnou
13 Jun 24 i i`- Re: "undefined behavior"?1David Brown
13 Jun 24 i `* Re: "undefined behavior"?15David Brown
13 Jun 24 i  `* Re: "undefined behavior"?14DFS
14 Jun 24 i   `* Re: "undefined behavior"?13David Brown
15 Jun 24 i    +* Re: "undefined behavior"?11DFS
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15 Jun 24 i    i `* Re: "undefined behavior"?9DFS
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15 Jun 24 i    i   `* Re: "undefined behavior"?7DFS
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15 Jun 24 i    i    +- Re: "undefined behavior"?1James Kuyper
15 Jun 24 i    i    +- Re: "undefined behavior"?1Keith Thompson
15 Jun 24 i    i    +- Re: "undefined behavior"?1bart
15 Jun 24 i    i    `- Re: "undefined behavior"?1David Brown
15 Jun 24 i    `- Re: "undefined behavior"?1David Brown
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