[Bug c/38046] 'warning: comparison between signed and unsigned' shouldn't be given for equality comparisons

[manu at gcc dot gnu dot org]

--- Comment #4 from manu at gcc dot gnu dot org  2010-02-24 14:29 ---
I am really sorry, I don't think we want to add an option for this particular
case. As Joseph explained, there is a difference if the variables are
mismatched signed/unsigned or not.

For your problem, you could use a wrapper around read() that does the cast.
Sorry, but this is not worth the overhead. Closing as WONTFIX.


-- 

manu at gcc dot gnu dot org changed:

   What|Removed |Added

 CC||manu at gcc dot gnu dot org
 Status|NEW |RESOLVED
 Resolution||WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38046

[Bug c/38046] 'warning: comparison between signed and unsigned' shouldn't be given for equality comparisons

[edwintorok at gmail dot com]

--- Comment #3 from edwintorok at gmail dot com  2008-11-07 17:14 ---
(In reply to comment #2)
 Subject: Re:   New: 'warning: comparison between signed and
  unsigned' shouldn't be given for equality comparisons
 
 On Fri, 7 Nov 2008, edwintorok at gmail dot com wrote:
 
  Consider this code:
  
  int foo(int a, unsigned b)
  {
  return a != b;
  }
 
  $ gcc -O2 -Wall -W foo.c -c
  foo.c: In function ‘foo’:
  foo.c:3: warning: comparison between signed and unsigned integer expressions
 
 Seems correct to me.  You could have a == -1 and b == UINT_MAX and they 
 would compare equal, but it's not at all obvious from the code that this 
 is the user's intent; and if it is their intent, they can use an explicit 
 cast.

It would be nice to have a separate warning option for ==, != comparisons, and
another for ,,=,= comparisons.

The problem is that with code that uses read(2) and write(2) you get lots of
warnings, and adding casts is time-consuming and of little benefit.
I'd like to turn -Wsign-compare into -Werror for 'make distcheck' in my
project, but can't do that due to the != comparisons. If I would have a
distinct -W flag for it, I could -Wno-error that.

 
  FWIW, if I change int to 'short int' or 'signed char' (and unsigned
  appropriately) I get no warning.
 
 Both short and unsigned short will be promoted to int before the 
 comparison, so you won't get -1 and USHRT_MAX comparing equal.
 

Ok


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38046

[Bug c/38046] 'warning: comparison between signed and unsigned' shouldn't be given for equality comparisons

[joseph at codesourcery dot com]

--- Comment #2 from joseph at codesourcery dot com  2008-11-07 12:46 ---
Subject: Re:   New: 'warning: comparison between signed and
 unsigned' shouldn't be given for equality comparisons

On Fri, 7 Nov 2008, edwintorok at gmail dot com wrote:

 Consider this code:
 
 int foo(int a, unsigned b)
 {
 return a != b;
 }

 $ gcc -O2 -Wall -W foo.c -c
 foo.c: In function ‘foo’:
 foo.c:3: warning: comparison between signed and unsigned integer expressions

Seems correct to me.  You could have a == -1 and b == UINT_MAX and they 
would compare equal, but it's not at all obvious from the code that this 
is the user's intent; and if it is their intent, they can use an explicit 
cast.

 FWIW, if I change int to 'short int' or 'signed char' (and unsigned
 appropriately) I get no warning.

Both short and unsigned short will be promoted to int before the 
comparison, so you won't get -1 and USHRT_MAX comparing equal.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38046

[Bug c/38046] 'warning: comparison between signed and unsigned' shouldn't be given for equality comparisons

[rguenth at gcc dot gnu dot org]

--- Comment #1 from rguenth at gcc dot gnu dot org  2008-11-07 11:26 ---
Confirmed.


-- 

rguenth at gcc dot gnu dot org changed:

   What|Removed |Added

   Severity|normal  |enhancement
 Status|UNCONFIRMED |NEW
 Ever Confirmed|0   |1
   Keywords||diagnostic
   Last reconfirmed|-00-00 00:00:00 |2008-11-07 11:26:49
   date||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38046