unions inside structures

[Chris Torek]

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 at umcp-cs		ARPA:	chris at maryland