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From: mneerach@iiic.ethz.ch (Matthias Ulrich Neeracher)
Newsgroups: comp.lang.c
Subject: Re: Novice question.
Message-ID: <14624@neptune.inf.ethz.ch>
Date: 14 Nov 90 09:56:11 GMT
References: <1990Oct31.014132.2400@agate.berkeley.edu> <336@brat.UUCP> <3838@vela.acs.oakland.edu>
Sender: news@neptune.inf.ethz.ch
Reply-To: mneerach@iiic.ethz.ch (Matthias Ulrich Neeracher)
Organization: Departement Informatik, ETH, Zurich
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In article <3838@vela.acs.oakland.edu> jmwojtal@vela.acs.oakland.edu (Wojo) writes:
>What exactly are the reasons "register" and "extrn" are used to declare
>values.  I see register alot in some of the programs and I don't know why
>they do it.  Is it just good practice or what.

"extern" essentially tells the compiler that this variable is defined 
elsewhere.

"register" is a hint to the compiler that this variable will be used a lot
and that the compiler should try to keep it in a processor register. This
hint was introduced in a time when programmers were smart and compilers were
stupid. Today, the opposite is true :-), so some compilers ignore "register"
hints completely and allocate registers as they see fit.

Matthias

-----
Matthias Neeracher                                   mneerach@iiic.ethz.ch
   "These days, though, you have to be pretty technical before you can 
    even aspire to crudeness." -- William Gibson, _Johnny Mnemonic_