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[Bug c/64518] New: Warning about comparison between signed and unsigned can be useless in some cases
- From: "patrick.pelissier at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 07 Jan 2015 09:04:04 +0000
- Subject: [Bug c/64518] New: Warning about comparison between signed and unsigned can be useless in some cases
- Auto-submitted: auto-generated
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)); }