Path: utzoo!attcan!uunet!taumet!steve
From: steve@taumet.com (Stephen Clamage)
Newsgroups: comp.lang.c++
Subject: Re: Need `set before used' warning
Keywords: c++, warning
Message-ID: <462@taumet.com>
Date: 27 Sep 90 16:12:49 GMT
References: <2@mtnmath.UUCP>
Organization: Taumetric Corporation, San Diego
Lines: 38

paul@mtnmath.UUCP (paul) writes:

>class Example {
>	char * Point ;
>public:
>	Example(char * point) {point=Point;}
>};

>There are two errors that it would be helpful to flag with
>warning messages.

>	1. Member variable `Point' is used before it is set.
>	2. Constructor parameter `point' which is not a reference
>	   is set before it is used.

>The latter message could apply to any subroutine definition, while
>the former is only valid for constructors.

>Is there some reason warnings of this sort should not be given?

No reason at all.  Some compilers do warn about these kinds of errors.
Oregon C++ (not an AT&T port) typically warns about variables used before
being set, but does not in this particular instance.  Turbo C++ (not an
AT&T port) warns about parameter "point" not being used, which is a more
correct statement than your #2 above.

Both compilers were derived from earlier compilers which did some flow
analysis to detect local variables used before being set.  The case of
a data member used before being set in a constructor requires a different
sort of test, and was evidently overlooked in these two compilers.

Non-dyslexics can also make the sort of error you have here, and it is
worth checking for, as a "quality of implementation" compiler issue.
However, this example is also an argument for choosing distinct
names, rather than "Point" and "point" which are easily confused.
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com