Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!brutus.cs.uiuc.edu!usc!ginosko!uunet!pilchuck!dataio!bright
From: bright@Data-IO.COM (Walter Bright)
Newsgroups: comp.lang.c++
Subject: Re: variable declaration
Keywords: variables, objects, optimization
Message-ID: <2125@dataio.Data-IO.COM>
Date: 13 Sep 89 18:51:32 GMT
References: <953@ncratl.Atlanta.NCR.COM>
Reply-To: bright@dataio.Data-IO.COM (Walter Bright)
Organization: Data I/O Corporation; Redmond, WA
Lines: 17

In article <953@ncratl.Atlanta.NCR.COM> brown@ncratl.Atlanta.NCR.COM (Kyle Brown) writes:
<In standard C (and other block-structured 
<languages) it's common to declare all variables in a block at the beginning
<of your program.  However, in C++ it is often useful to declare some
<variables close to their first point of use.
<Has anybody developed any style rules for this?

Declare variables in the innermost set of {} that you can. This improves
both readability and optimizability (for compilers that can't do live
range analysis).

The idea is to reduce the scope of the variable to a minimum. Readability
is enhanced because it reduces the number of lines of code you have to scan
to figure out all the uses of a variable. Reducing the scope improves the
possibility that the optimizer could share its storage with another variable
that has a non-intersecting scope (which can result in more variables going
into registers!).