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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Sort of trivial code challenge - may be interesting to you anyway
Date: Wed, 11 Mar 2026 07:07:09 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> scott@slp53.sl.home (Scott Lurndal) writes:
>
>> DFS <nospam@dfs.com> writes:
>>
>>> On 3/8/2026 3:29 PM, Bart wrote:
>>>
>>>> note that setjmp/longjmp are not functions
>>>
>>> huh?
>>>
>>> https://man7.org/linux/man-pages/man3/longjmp.3.html
>>
>> POSIX allows setjmp to be defined as a macro.
>>
>> https://pubs.opengroup.org/onlinepubs/9799919799/functions/setjmp.html
>
> More to the point, ISO C (all editions from C90 to C23) specifies that
> setjmp is a macro, and longjmp is a function.  (Like any library
> function, longjmp can *also* be implemented as a macro).
>
> As it happens, glibc's <setjmp.h> has:
>
>     #define setjmp(env)     _setjmp (env)
>
> where _setjmp is a function.
>
> POSIX says:
>
>     It is unspecified whether setjmp() is a macro or a function.  If
>     a macro definition is suppressed in order to access an actual
>     function, or a program defines an external identifier with the
>     name setjmp, the behavior is undefined.
>
> which may be inconsistent with ISO C.

The original ANSI C standard says this:

    It is unspecified whether setjmp is a macro or an identifier
    declared with external linkage.  If a macro definition is
    suppressed in order to access an actual function, or a program
    defines an external identifier with the name setjmp, the
    behavior is undefined.

I think every version of the ISO C standard says exactly the same
thing.  I did a quick check but didn't verify that the wording is
exactly identical in every case.