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[Bug c/51294] New: spurious warning from -Wconversion in C and C++
- From: "tortoise_74 at yahoo dot co.uk" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 24 Nov 2011 11:33:57 +0000
- Subject: [Bug c/51294] New: spurious warning from -Wconversion in C and C++
- Auto-submitted: auto-generated
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51294
Bug #: 51294
Summary: spurious warning from -Wconversion in C and C++
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: tortoise_74@yahoo.co.uk
The code below produces a spurious warning when compiled with -Wconversion.
0 is a const so the compiler should be able to choose the correct type. This
works with gcc 4.1 on redhat 5 but not the latest snapshot of gcc 4.7 (which I
am trialing for its c++11 support).
I do not have any intermediate compiler versions to test with.
spurious.cpp:
class foo
{
char bar;
foo(bool haveBar, char bar_):
bar(haveBar?bar_:0)
{
}
};
##
test.sh
#!/bin/sh
gcc --version
gcc -Wconversion -c spurious.cpp
export LD_LIBRARY_PATH=/opt/gcc4.7/lib:$LD_LIBRARY_PATH
export PATH=/opt/gcc4.7/bin:$PATH
/opt/gcc4.7/bin/gcc --version
/opt/gcc4.7/bin/gcc -Werror -Wconversion -c spurious.cpp
##
brucea@:home/brucea/spurious>./test.sh
gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-51)
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
gcc (GCC) 4.7.0 20111119 (experimental)
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
spurious.cpp: In constructor âfoo::foo(bool, char)â:
spurious.cpp:8:25: error: conversion to âcharâ from âintâ may alter its value
[-Werror=conversion]
cc1plus: all warnings being treated as errors
##
The workaround is either to disable the warning with -Wno-conversion or add
unecessary constants as below. I don't think this is acceptable.
class foo2
{
static const char zero = 0;
char bar;
foo2(bool haveBar, char bar_):
bar(haveBar?bar_:zero)
{
}
};
This is also a bug in the C front-end:
void foo(int haveBar, char bar_)
{
char zuul = haveBar?bar_:0;
}