From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jim Wilson <wilson@chestnut.cygnus.com>
To: Ian Lance Taylor <ian@cygnus.com>
Cc: rms@gnu.ai.mit.edu, drepper@cygnus.com, dm@sgi.com, gcc2@cygnus.com, gas2@cygnus.com
Subject: Re: global vars and symbol visibility for mips32/elf 
Date: Sat, 10 Aug 1996 23:26:00 -0000
Message-id: <199608110626.XAA06107@cygnus.com>
References: <9608110241.AA22482@tweedledumb.cygnus.com>
X-SW-Source: 1996/msg00083.html

	The case which causes trouble is when a program uses a common variable
	(an uninitialized variable in C; most languages, including C++, have
	no notion of common variables).

ANSI/ISO C also does not have common variables.  A program with multiple
external definitions of a variable has undefined behaviour.  However, C
compilers that make this work by treating uninitialized variables as
common are so prevalent that most people aren't aware of this.  This
particular feature is mentioned in the `Common Extensions' appendix, in
the section `Multiple External Definitions'.

This also means that, technically, if you want to make sure that other
ANSI/ISO C compilers can compile your code, you must use -fno-common
in addition to -ansi and -pedantic.

Jim