Date: Wed, 10 Jul 2013 20:32:00 +0200 From: "O. Hartmann" <ohartman@zedat.fu-berlin.de> To: David Chisnall <theraven@FreeBSD.org> Cc: FreeBSD CURRENT <freebsd-current@FreeBSD.org>, freebsd-toolchain@FreeBSD.org Subject: Re: CURRENT: CLANG 3.3 and -stad=c++11 and -stdlib=libc++: isnan()/isninf() oddity Message-ID: <20130710203200.5359fd18@thor.walstatt.dyndns.org> In-Reply-To: <C8C94CF2-7D5A-471B-AD63-8E961AED6274@FreeBSD.org> References: <20130710155809.0f589c22@thor.walstatt.dyndns.org> <CD51F125-AE9E-4461-916D-CF583002B47D@FreeBSD.org> <20130710183315.725dfde0@thor.walstatt.dyndns.org> <C8C94CF2-7D5A-471B-AD63-8E961AED6274@FreeBSD.org>
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On Wed, 10 Jul 2013 18:04:16 +0100
David Chisnall <theraven@FreeBSD.org> wrote:
> On 10 Jul 2013, at 17:33, "O. Hartmann" <ohartman@zedat.fu-berlin.de>
> wrote:
>=20
> > Hi David,
> >=20
> > thanks for the fast response.
> >=20
> > The code I was told to check with is this:
> >=20
> > #include <iostream>
> > #include <typeinfo>
> > #include <cmath>
> >=20
> > int
> > main(void)
> > {
> >=20
> > std::cout << typeid(isnan(1.0)).name() << "\n";
> >=20
> > }
> >=20
> >=20
> > If I compile it with=20
> >=20
> > c++ -o testme -std=3Dc++11 -stdlib=3Dlibc++ source.cc
> >=20
> > and run the binary, the result is "i" which I interpret as "INT".
>=20
> I believe there is a bug, which is that the math.h things are being
> exposed but shouldn't be, however it is not the bug that you think it
> is. Try this line instead:
>=20
> std::cout << typeid(std::isnan(1.0)).name() << "\n";
>=20
> We have a libm function, isnan(), and a libc++ function,
> std::isnan(). The former is detected if you do not specify a
> namespace. I am not sure what will happen if you do:
>=20
> #include <iostream>
> #include <typeinfo>
> #include <cmath>
> using namespace std;
>=20
> int
> main(void)
> {
>=20
> cout << typeid(isnan(1.0)).name() << "\n";
>=20
> }
>=20
> This is considered bad form, but does happen in some code. I am not
> certain what the precedence rules are in this case and so I don't
> know what happens.
>=20
> To properly fix this, we'd need to namespace the libm functions when
> including math.h in C++. This would also include fixing tweaking the
> macros. =20
>=20
> A fix for your code is to ensure isnan() and isinf() are explicitly
> namespaced. Potentially, this may also work:
>=20
> using std::isinf;
> using std::isnan;
>=20
> David
>=20
I tried in the test code I provided using=20
#include <iostream>
#include <typeinfo>
#include <cmath>
int
main(void)
{
std::cout << typeid(std::isnan(1.0)).name() << "\n";
}
now std::isnan().
The result is the same, it flags "INT".
Using=20
#include <iostream>
#include <typeinfo>
#include <cmath>
using namespace std;
int
main(void)
{
std::cout << typeid(std::isnan(1.0)).name() << "\n";
}
which is considered "bad coding" also results in "INT" (it gives "i").
So, is this woth a PR?
Oliver
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