[Bug c++/41274] New: Some -Wconversion warnings are almost impossible to fix
ashaduri at gmail dot com
gcc-bugzilla@gcc.gnu.org
Sat Sep 5 12:19:00 GMT 2009
Some -Wconversion warnings are just useless and almost impossible to fix.
Consider the following example:
--------------------------------------------------------------------
template <typename T> inline
void add_to_v1(T& v1, const T& v2)
{
v1 += v2; // warning: conversion to Âshort int from Âint may alter
its value
}
int main()
{
{
short i1 = 0;
short i2;
i1 += i2; // warning: conversion to Âshort int from Âint may
alter its value
}
{
short i1 = 0;
short i2;
i1 /= i2; // warning: conversion to Âshort int from Âint may
alter its value
}
{
char c1 = 0;
char c2;
c1 += c2; // warning: conversion to Âchar from Âint may
alter its value
}
{
short v1;
add_to_v1(v1, (short)2); // see function template above
}
return 0;
}
--------------------------------------------------------------------
As you can see, a simple += operator between short integers causes the warning,
which is, of course, a standard C/C++ feature with defined behaviour. Same goes
for the other ones, like /= operator.
The worse thing about it is that it's impossible to shut it up when using
function templates, without making specializations for every type for which
sizeof(T) < sizeof(int). The += operator in the function template above is
expected to work with any T supporting operator+=. Instead, we get an
essentially non-fixable warning there. Since a+=b and a=a+b mean different
things depending on type, such warnings cannot be fixed with static_cast.
gcc version 4.4.1 [gcc-4_4-branch revision 150839] (SUSE Linux)
--
Summary: Some -Wconversion warnings are almost impossible to fix
Product: gcc
Version: 4.4.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ashaduri at gmail dot com
GCC build triplet: x86_64-suse-linux
GCC host triplet: x86_64-suse-linux
GCC target triplet: x86_64-suse-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41274
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