Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!brl-adm!seismo!rochester!cornell!batcomputer!braner
From: braner@batcomputer.UUCP
Newsgroups: comp.lang.c
Subject: Re: Auto variable with sizeof == 0
Message-ID: <159@batcomputer.tn.cornell.edu>
Date: Wed, 11-Feb-87 01:15:47 EST
Article-I.D.: batcompu.159
Posted: Wed Feb 11 01:15:47 1987
Date-Received: Thu, 12-Feb-87 00:02:05 EST
References: <4114@brl-adm.ARPA> <4053@utcsri.UUCP>
Reply-To: braner@batcomputer.UUCP (braner)
Organization: Theory Center, Cornell University, Ithaca NY
Lines: 37
Summary: How about structure elements with size 0?

[]

In the famous "microEMACS" by David Conroy, which has been widely
utilized and modified, the basic text-line structure looks like this:

typedef struct LINE {
	struct LINE *nextline;
	struct LINE *prevline;
	short       size;		/* s.b. int! */
	short       used;
	char        text[];		/* !!!!!!!!! */
}	LINE;

The idea is to allocate memory for lines as follows:

	lineptr = malloc(sizeof(LINE)+length);

where length is as needed at the time for that line.  The actual text
of the line is stored OUTSIDE the struct, starting at lineptr->text[0].
This is, of course, "illegal".  Some compilers give a warning about
"zero-size structure element".

Question:  Do some compilers refuse to accept this?  Is there a GOOD
way to do it legally?  (NOTE: I KNOW that you can use:

	...
	char	*text;
	...
	lineptr = malloc(sizeof(LINE));
	lineptr->text = malloc(length);

- but the illegal version saves the overhead of the extra pointer and
the overhead of the extra malloc() control block.  In this application
this saving is important, since there will be hundreds or even thousands
of LINEs.)

- Moshe Braner