NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/10404

Internet Message Format | 1996-08-05 | 1.5 KB

Path: keats.ugrad.cs.ubc.ca!not-for-mail
From: [e-mail] (Kazimir Kylheku)
Newsgroups: comp.lang.c
Subject: Re: Non arithmetic integer type.
Date: 17 Mar 1996 08:45:32 -0800
Organization: Computer Science, University of B.C., Vancouver, B.C., Canada
Message-ID: <[e-mail]>
References: <4igp11$[e-mail]>
NNTP-Posting-Host: keats.ugrad.cs.ubc.ca

In article <4igp11$[e-mail]>,
Simon Hosie <[e-mail]> wrote:
 >  I've been trying to create a data type that holds an int or intlike chunk
 >of data that is incompatible with any other types (to generate errors if
 >someone assumes that it's the same type as an int).. I've found that
 >
 >typedef struct { int Value; } TypeA;
 >typedef struct { int ValueWithADifferentName; } TypeB;
 >
 >  makes two compatible types; a variable of TypeA can be assigned to a
 >variable of TypeB without any warnings.. but

Your compiler has a gratuitous extension that allows for structural
equivalence type checking.

In standard C, structures with a different tag name are different.  Structures
declard with _no tag_ are always incompatible with each other and with other
structures that have tags.

An assignment between TypeA and TypeB shouldn't even compile.

 >typedef struct { int Value; } TypeA;
 >typedef struct { unsigned Value; } TypeB;
 >
 >  is incompatible, which is what I want and it works.. but what if I want
 >three or more incompatible types?

Get a compiler that adheres to the standard, or find an option in your compiler
to make it do so.

--