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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Set the result of void function
Date: Tue, 19 Sep 2017 19:36:23 -0700
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Thiago Adams <thiago.adams@gmail.com> writes:
> Can I set the result of some void function and get it back?

A void function doesn't have a result.  You can pass information out of
it in a number of other ways.

[...]

> I can do the opposite that is not set the result:
>
> int F()
> {
>     goto END;
>     if (0)
>         return 1;
>     END:;
> }
>
> int main()
> {
>   int i = F();
> }

N1570 6.9.1p12:

    If the } that terminates a function is reached, and the value of the
    function call is used by the caller, the behavior is undefined.

There's no need for the goto statement in your example.  This:

    int F(void) { }

does the same thing.

(The reason it's not a constraint violation is that in pre-ANSI C, void
didn't exist, and a function not intended to return a value would be
defined with a return type of int.  It was up to the caller to avoid
using the meaningless result.)

-- 
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"