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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: function pointer question
Date: Sat, 03 Jan 2026 16:48:08 -0800
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James Kuyper <jameskuyper@alumni.caltech.edu> writes:
[...]
> Similarly, in C, the declaration "int foo()" is an old-style K&R
> declaration that says that foo is a function that takes an unspecified
> number of arguments of unspecified types. K&R declarations were found to
> be too error-prone, but the language still allows them for backwards
> compatibility. When C was first standardized, K&R declarations were
> replace with prototype declarations which specified the type of each
> argument, which allowed error checking.
> The natural way for a prototype declaration to say "no arguments" would
> have been to simply specify no arguments, and C++ uses that approach.
> However, since C still supports the old K&R declarations, a different
> method was used. "int foo(void)" is a function prototype that says that
> foo doesn't take any arguments.
[...]

Some of this changed in C23.  I don't have all the details off the top
of my head, but as I understand it old-style function definitions
are no longer allowed and `int foo()` is equivalent to `int foo(void)`.

(Which means, I think, that my argument that `int main()` has undefined
behavior does not apply in C23.)

It's still not a bad idea to write (void) on a parameterless function
declaration/definition unless you're sure your code will be compiled
only with a compiler that implements C23 or later.

The 2023 ISO C standard is expensive, but the closest draft is:

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf

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