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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: function pointer question
Date: Fri, 02 Jan 2026 02:52:22 -0800
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Michael Sanders <porkchop@invalid.foo> writes:
> i have:
>
> void moo(char HISTORY[][64], int hst_len, int invalid, const char *gme_msg)
>
> void mastermind(char HISTORY[][64], int hst_len, int invalid, const char *gme_msg)
>
> to use either i have:
>
> void (*render)(char [][64], int, int, const char *) = MOO ? moo : mastermind;
>
> my multi-part question:
>
> why is void required for the function pointer?

Every function has a type.  Every function pointer has a type.  For a
function pointer to point to a function, it must have type "pointer to
blah", where "blah" is the type of the function.

A function type includes information about the type of the function's
result and the types of its parameters.  The type of both foo and
mastermind can be written as:

    void(char[]64], int, int, const char*)

> A: because both moo() & mastermind return void?

Yes.

> B: because every function must have a return type
>    *including function pointers*?

Functions and function pointers are of course distinct.  A function is
of function type.  A function pointer is of an object type, specifically
a pointer-to-function type.

Every pointer-to-function type is derived from a function type, and that
function type specifies the type returned by the function -- "void" in
this case.

> C: what about tyedef?

What about it?

You can define a typedef for the function type, which could make the
code a bit simpler.  (It's also common to define a typedef for a
pointer-to-function type, but I prefer to typedef the function type
itself.)

An example based on your code :

```
#include <stdio.h>

void moo(char HISTORY[][64], int hst_len, int invalid, const char *gme_msg) {
    puts("moo");
}

void mastermind(char HISTORY[][64], int hst_len, int invalid, const char *gme_msg) {
    puts("mastermind");
}

typedef void functype(char [][64], int, int, const char *);

int main(void) {
    for (int MOO = 0; MOO < 2; MOO ++) {
        functype *render = MOO ? moo : mastermind;
        printf("MOO is %s: ", MOO ? "true" : "false");
        render(NULL, 0, 0, "");
    }
}
```

The output :

```
MOO is false: mastermind
MOO is true: moo
```

(Incidentally, all-caps identifiers are most commonly used as macro
names, with FILE being a notable exception.)

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