NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/3226

Internet Message Format | 1996-08-05 | 1.8 KB

Path: castle.nando.net!news
From: [e-mail]   (Bill McCarthy)
Newsgroups: comp.lang.c
Subject: Re: Can a function return a (pointer to a) function?
Date: 27 Jan 1996 02:56:12 GMT
Organization: News & Observer Public Access
Message-ID: <4ec48c$[e-mail]>
References: <4ebaaa$[e-mail]>
Reply-To: [e-mail] (Bill McCarthy)
NNTP-Posting-Host: vyger513.nando.net
X-Newsreader: IBM NewsReader/2 v1.2

In <4ebaaa$[e-mail]>,
"John D. Hourihane" <[e-mail]> writes:

>I am trying to write a function which will return a pointer to a function,
>but I'm having no luck.
>
>The toy program below illustrates (I hope) what I want to be able to do,
>but as it stands it won't compile for me. The idea is that the call to
>'(pick(ADD))' will return a pointer to the 'add' function which is then
>dereferenced and used.
>
>But like I say, it doesn't compile. It complains 'Declaration terminated
>incorrectly' as I declare 'pick'. I'm using Turbo C/C++.
>
>Any reply, posted here or by email, would be great.
>
>/* The toy program, to use a function that returns a
> * pointer to a function.
> */
>
>#include <stdio.h>
>
>#define ADD            0
>#define MULTIPLY    1
>
>int add(int x, int y);
>int multiply(int x, int y);
>
>/* pick returns a pointer to a function which will operate on two integers */
>(int f(int, int)) *pick(int s);

Replace above with:

    int (*pick(int))(int, int);

>
>int main()
>{
>    printf("5 + 4 = %d\n", (*(pick(ADD)))(5,4));
>    printf("5 * 4 = %d\n", (*(pick(MULTIPLY)))(5,4));
>    return 0;
>}
>
>int add(int x, int y)
>{    return x + y; }
>
>int multiply(int x, int y)
>{    return x * y; }
>
>(int f(int, int)) *pick(int s)

And replace the above line with:

    int (*pick(int s))(int, int)

>{    if (s == ADD)
>        return add;
>    return multiply;
>}

Bill McCarthy
[e-mail]
Wendell, NC  USA