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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Abstract Syntax Tree for C programs
Date: Tue, 04 Jun 2019 11:55:27 -0700
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Xref: csiph.com comp.lang.c:144421

Bart <bc@freeuk.com> writes:
> On 04/06/2019 07:56, Ike Naar wrote:
>> On 2019-06-03, Bart <bc@freeuk.com> wrote:
>>> Using a void* to store a void(*)(void) is not a big deal, you don't want
>>> -pedantic-errors to stop your build because of it.
>> 
>> Using a function pointer (and not an object pointer) to store a
>> function pointer isn't a big deal either.
>> 
>
> How would you create the following table:
>
>    void fn1(void){}
>    void fn2(int a){}
>    void fn3(int a,double b){}
>    int fn4(void){return 0;}
>    char* fn5(double a){return "";}
>
>    void* table[] = {fn1,fn2,fn3,fn4,fn5};
>
> Suggestions to use void(*)(void) for the table element aren't as good.
>
> (Because you could actually write table[3]() without the compiler 
> picking that up.
[...]

I'd probably write it something like this:

    void fn1(void){}
    void fn2(int a){}
    void fn3(int a,double b){}
    int fn4(void){return 0;}
    char* fn5(double a){return "";}

    struct do_not_use { char dummy; };
    typedef void generic_function(struct do_not_use);

    generic_function *const table[] = {
        (generic_function*)fn1,
        (generic_function*)fn2,
        (generic_function*)fn3,
        (generic_function*)fn4,
        (generic_function*)fn5,
    };

(I added the "const" to prevent accidental modifications of the
elements.  Remove it if you want to be able to modify them.)

`table[0]()` is rejected with a "too few arguments" error.

[...]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */