Path: utzoo!mnetor!lazer
From: lazer@mnetor.UUCP (Lazer Danzinger)
Newsgroups: comp.lang.c
Subject: Re: cast'ing unions
Message-ID: <5068@mnetor.UUCP>
Date: 29 Aug 89 19:38:13 GMT
References: <2189@stl.stc.co.uk=>
Reply-To: lazer@mnetor.UUCP (Lazer Danzinger)
Organization: Motorola Computer X
Lines: 36

In article <2189@stl.stc.co.uk=> dsr@stl.stc.co.uk (David Riches) writes:
=>
=>union
=>{
=>   int i ;
=>   float f ;
=>   char* c ;
=>}
=>UNION ;
=>
=>UNION u ;
=>u.i = 1 ;
=>
=>Is it possible in C to typecast from an instance of the union to a variable
=>having the same type as one of the component fields of the union :
=>
=>ie float num = (float) u ;
=>
=>I tried the above but got compiler errors. Am I doing the typecast wrong,
=>or do I need to use another method to achieve the above, or is it not
=>possible to do the typecast directly ??
=>
    1. UNION, as specified above, is not a new data type name, but a (union)
       variable. Hence, the "UNION u;" statement will generate a syntax
       error. (Unless you say: typedef union .
    2. Assuming that "u" is indeed a union variable, then the following
       works:
       num = *(float *)&u;

    My example is consistent with the restrictions place upon unions, as
    specified in K&R, pg. 140:
	"...the only operations currently permitted on unions are accessing
	a member and taking the address..."

    ANSI 'C' may be more tolerant.