public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "patrick.pelissier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/64518] New: Warning about comparison between signed and unsigned can be useless in some cases
Date: Wed, 07 Jan 2015 09:04:00 -0000	[thread overview]
Message-ID: <bug-64518-4@http.gcc.gnu.org/bugzilla/> (raw)

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64518

            Bug ID: 64518
           Summary: Warning about comparison between signed and unsigned
                    can be useless in some cases
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick.pelissier at gmail dot com

For the following function:

int f(int x) { return ( x >= 0 && x < sizeof(int)); } 


I get the following warning with gcc -Wsign-compare -c f.c :
f.c: In function 'f':
f.c:1:37: warning: comparison between signed and unsigned integer expressions
[-Wsign-compare]
 int f(int x) { return ( x >= 0 && x < sizeof(int)); } 
                                     ^


However, as x has been checked as positive due to the first comparison, I don't
see how the comparison between x (signed) and sizeof(int) (unsigned) can be
wrong.

The proposed enhancement is to improve the warning to handle this case properly
without adding a (useless) cast in the user code like this:

int f(int x) { return ( x >= 0 && (unsigned int) x < sizeof(int)); }


                 reply	other threads:[~2015-01-07  9:04 UTC|newest]

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bug-64518-4@http.gcc.gnu.org/bugzilla/ \
    --to=gcc-bugzilla@gcc.gnu.org \
    --cc=gcc-bugs@gcc.gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).