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* [Bug c++/26298] New: no warning for implicit type conversion
@ 2006-02-15 9:10 m dot becker at spider-software dot net
2006-02-15 10:36 ` [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion rguenth at gcc dot gnu dot org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: m dot becker at spider-software dot net @ 2006-02-15 9:10 UTC (permalink / raw)
To: gcc-bugs
The following code gives two different results without any warning:
#include <stdio.h>
void toInt(int i)
{
fprintf(stderr, "i = %d\n", i);
}
void toLongLong(long long L)
{
fprintf(stderr, "L = %lld\n", L);
}
int main()
{
toInt(-sizeof(int));
toLongLong(-sizeof(int));
return 0;
}
There should at least be a warning.
This behaviour can be found on SUN and on Linux x86 with compiler versions
between 3.4.4 and 4.0.3 (prerelease).
--
Summary: no warning for implicit type conversion
Product: gcc
Version: 4.0.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: m dot becker at spider-software dot net
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26298
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion
2006-02-15 9:10 [Bug c++/26298] New: no warning for implicit type conversion m dot becker at spider-software dot net
@ 2006-02-15 10:36 ` rguenth at gcc dot gnu dot org
2006-09-16 1:38 ` lopezibanez at gmail dot com
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2006-02-15 10:36 UTC (permalink / raw)
To: gcc-bugs
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------- Comment #1 from rguenth at gcc dot gnu dot org 2006-02-15 10:36 -------
With -Wconversion you get
t.c:5: warning: passing argument 1 of toLongLong with different width due to
prototype
though -Wconversion is neither in -Wall nor -Wextra. I see you filed against
C++, which doesn't warn here, but we have a bug for a similar case already.
Also the C diagnostic could be improved in the case of a widening sign
conversion,
because that is more likely an error than a non-widening sign conversion.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
BugsThisDependsOn| |26167
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Keywords| |diagnostic
Last reconfirmed|0000-00-00 00:00:00 |2006-02-15 10:36:07
date| |
Summary|no warning for implicit type|-Wconversion fails to detect
|conversion |signedness change during
| |widening conversion
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26298
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion
2006-02-15 9:10 [Bug c++/26298] New: no warning for implicit type conversion m dot becker at spider-software dot net
2006-02-15 10:36 ` [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion rguenth at gcc dot gnu dot org
@ 2006-09-16 1:38 ` lopezibanez at gmail dot com
2006-09-16 17:08 ` rguenth at gcc dot gnu dot org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: lopezibanez at gmail dot com @ 2006-09-16 1:38 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from lopezibanez at gmail dot com 2006-09-16 01:38 -------
Richard, could you tell which bug report do you mean?
The -Wconversion warnings does not apply to this case. Wconversion warns about
the effect of adding a prototype, not about sign conversions.
Anyway, I still don't understand where is the bug. Unary minus applied to
unsigned (what typically is the type of sizeof()) gives:
" `2^n - i', where `n' is the number of bits in the
unsigned type." [1]
So actually -sizeof(int) is 4294967292 (assuming sizeof(int) is 4). This number
fits well in a signed long long. However, it doesn't fit in a signed int, and
thus, it wraps around and produces -4.
The -Wcoercion flag provided by the Wcoercion project [2] warns for the
wrap-around as:
pr26298.c:15: warning: coercion as 'int' alters 'unsigned int' constant value
[1] http://gcc.gnu.org/ml/gcc/1999-06n/msg00754.html
[2] http://gcc.gnu.org/wiki/Wcoercion
--
lopezibanez at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |lopezibanez at gmail dot
| |com, rguenth at gcc dot gnu
| |dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26298
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion
2006-02-15 9:10 [Bug c++/26298] New: no warning for implicit type conversion m dot becker at spider-software dot net
2006-02-15 10:36 ` [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion rguenth at gcc dot gnu dot org
2006-09-16 1:38 ` lopezibanez at gmail dot com
@ 2006-09-16 17:08 ` rguenth at gcc dot gnu dot org
2006-09-16 19:45 ` lopezibanez at gmail dot com
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2006-09-16 17:08 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from rguenth at gcc dot gnu dot org 2006-09-16 17:08 -------
26167, the one I added in the dependencies
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26298
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion
2006-02-15 9:10 [Bug c++/26298] New: no warning for implicit type conversion m dot becker at spider-software dot net
` (2 preceding siblings ...)
2006-09-16 17:08 ` rguenth at gcc dot gnu dot org
@ 2006-09-16 19:45 ` lopezibanez at gmail dot com
2006-09-17 21:02 ` rguenth at gcc dot gnu dot org
2006-10-16 15:37 ` mueller at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: lopezibanez at gmail dot com @ 2006-09-16 19:45 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from lopezibanez at gmail dot com 2006-09-16 19:45 -------
Richard,
and what is your opinion about the rest of my comment?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26298
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion
2006-02-15 9:10 [Bug c++/26298] New: no warning for implicit type conversion m dot becker at spider-software dot net
` (3 preceding siblings ...)
2006-09-16 19:45 ` lopezibanez at gmail dot com
@ 2006-09-17 21:02 ` rguenth at gcc dot gnu dot org
2006-10-16 15:37 ` mueller at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2006-09-17 21:02 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from rguenth at gcc dot gnu dot org 2006-09-17 21:02 -------
Well, you are right. This bug is a dup of the bug requesting -Wcoercion (if we
have such).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26298
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion
2006-02-15 9:10 [Bug c++/26298] New: no warning for implicit type conversion m dot becker at spider-software dot net
` (4 preceding siblings ...)
2006-09-17 21:02 ` rguenth at gcc dot gnu dot org
@ 2006-10-16 15:37 ` mueller at gcc dot gnu dot org
5 siblings, 0 replies; 7+ messages in thread
From: mueller at gcc dot gnu dot org @ 2006-10-16 15:37 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from mueller at gcc dot gnu dot org 2006-10-16 15:37 -------
*** This bug has been marked as a duplicate of 26167 ***
--
mueller at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |DUPLICATE
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26298
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2006-10-16 15:37 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2006-02-15 9:10 [Bug c++/26298] New: no warning for implicit type conversion m dot becker at spider-software dot net
2006-02-15 10:36 ` [Bug c++/26298] -Wconversion fails to detect signedness change during widening conversion rguenth at gcc dot gnu dot org
2006-09-16 1:38 ` lopezibanez at gmail dot com
2006-09-16 17:08 ` rguenth at gcc dot gnu dot org
2006-09-16 19:45 ` lopezibanez at gmail dot com
2006-09-17 21:02 ` rguenth at gcc dot gnu dot org
2006-10-16 15:37 ` mueller at gcc dot gnu dot org
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