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From: john@chinet.chi.il.us (John Mundt)
Newsgroups: comp.lang.c
Subject: Re: Functions within structures
Keywords: structures
Message-ID: <1990Nov10.155153.20639@chinet.chi.il.us>
Date: 10 Nov 90 15:51:53 GMT
References: <2203@abcom.ATT.COM>
Organization: Chinet - Public Access UNIX
Lines: 59

In article <2203@abcom.ATT.COM> mdb@abcom.ATT.COM (5013 ) writes:
>   I need help.  I am building a menu using structures and would like
>   to be able to include the function to be run within the structure.

	....

> 
>int   add_rec();
>int   find_rec();
>int   quit();
> 
>unsigned	int	records=0;
>typedef struct {
>   char    key;
>   int     x_row;
>   int     y_row;
>   char    msg[20];
    int (*fptr)();	/* add this to your structure prototype */
>} MENU;
> 
>MENU menu[MENU_ITEM+1] = {
>    { '1',7,25,"Add Phone Number",add_rec },
>    { '2',9,25,"Find Phone number",find_rec },
>    { 'Q',12,25,"QUIT",quit }
>    } ;

Notice that the ()'s were removed from the functions.

> 
>Now, how do I assigned these functions to the structure (or is it posible)
>and then access these same functions?  Any help will be greatly appreciated.

The functions are now assigned, so that menu[whatever].fptr is the
function.  You can use the function thusly,

	{
		int some_value;
		some_value = (*menu[whatever].fptr)();
	}

since menu[whatever].fptr is the address of the function, and
*menu[whatever].fptr is the function.  K&R says it better.

Lint and/or your compiler may or may not complain about this.  Seems
to depend on the machine.  3b2's like it, 3b1's do not.  386's don't
like it, but in all cases it works.  

As an aside,

		some_value = (*menu[whatever].fptr)();
		some_value = (menu[whatever].fptr)();

produce the same assembler code on at least one machine, and both
work, though the first one is the one that is considered correct.
-- 
---------------------
john@admctr.chi.il.us
John Mundt   Teachers' Aide, Inc.  P.O. Box 1666,  Highland Park, IL
(708) 998-5007 || -432-8860