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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.lang.c
Subject: Re: unions inside structures
Message-ID: <2606@umcp-cs.UUCP>
Date: Sat, 19-Jan-85 19:15:30 EST
Article-I.D.: umcp-cs.2606
Posted: Sat Jan 19 19:15:30 1985
Date-Received: Mon, 21-Jan-85 02:45:59 EST
References: <133@ISM780B.UUCP> <10975@watmath.UUCP>
Organization: U of Maryland, Computer Science Dept., College Park, MD
Lines: 51

Concerning the problem of ``invented names'':

Suppose you need a structure to hold either a character/font pair, or
an adjustment.  Then you might write

	enum node_type { ntype_char, ntype_adjust };

	struct char_node {
	    char cn_char;
	    char cn_font;
	};

	struct node {
	    enum node_type n_type;	/* is it a char or an adjust? */
	    union {
		struct char_node un_char;/* value if char */
		short un_adj;		/* value if adjust */
	    } n_un;
	};

(Note the ``invented name'' n_un.)

Then a reasonable compromise for accessing the fields of a struct node
is to create the definitions

	#define n_char	n_un.un_char
	#define n_adj	n_un.un_adj

You can then write

	put(np)
	struct node *np;
	{

		if (np->n_type == ntype_char) {
			select_font(np->n_char.cn_font);
			put_char(np->n_char.cn_char);
		}
		else
			do_adj(np->n_adj);
	}

which makes the ``n_un.un'' part of each name vanish.  Admittedly
this has problems, but it can improve readability---and it requires
no changes to the language.
-- 
(This line accidently left nonblank.)

In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
UUCP:	{seismo,allegra,brl-bmd}!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@maryland