C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  NaN and inf literal constants g++          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Jon Wilson Guest Posted: Fri Dec 31, 2004 2:41 am    Post subject: NaN and inf literal constants g++ How do I write Not A Number or +/- infinity (floating point values) as literal constants (I'm using g++)? I have a function that returns float, and I need a flag value, and for various reasons one of NaN, +/-inf would be most convenient. But how do I tell my function to return one of these? The best I can come up with so far is float foo() { if(bar) return (2 + 2); else return (0.0 / 0.0); } Which works, ( (0.0 / 0.0) == NaN, or (1.0 / 0.0) == inf ), but g++ gives me a divide-by-zero warning when I compile. Regards, Jon Back to top Victor Bazarov Guest Posted: Fri Dec 31, 2004 4:02 am    Post subject: Re: NaN and inf literal constants g++ "Jon Wilson" <jsw (AT) fnal (DOT) gov> wrote... Quote: How do I write Not A Number or +/- infinity (floating point values) as literal constants (I'm using g++)? I have a function that returns float, and I need a flag value, and for various reasons one of NaN, +/-inf would be most convenient. But how do I tell my function to return one of these? The best I can come up with so far is float foo() { if(bar) return (2 + 2); else return (0.0 / 0.0); } Which works, ( (0.0 / 0.0) == NaN, or (1.0 / 0.0) == inf ), but g++ gives me a divide-by-zero warning when I compile. Take a look at std::numeric_limits template, there are static member functions for NaN, infinity, and other things. You won't need to do anything as weird as what you've shown. V Back to top Walter Guest Posted: Fri Dec 31, 2004 7:11 am    Post subject: Re: NaN and inf literal constants g++ "Victor Bazarov" <v.Abazarov (AT) comAcast (DOT) net> wrote Quote: "Jon Wilson" <jsw (AT) fnal (DOT) gov> wrote... How do I write Not A Number or +/- infinity (floating point values) as literal constants (I'm using g++)? I have a function that returns float, and I need a flag value, and for various reasons one of NaN, +/-inf would be most convenient. But how do I tell my function to return one of these? The best I can come up with so far is float foo() { if(bar) return (2 + 2); else return (0.0 / 0.0); } Which works, ( (0.0 / 0.0) == NaN, or (1.0 / 0.0) == inf ), but g++ gives me a divide-by-zero warning when I compile. Take a look at std::numeric_limits template, there are static member functions for NaN, infinity, and other things. You won't need to do anything as weird as what you've shown. Digital Mars C++ has the keyword __inf representing double infinity, and __nan representing double NaN. (For C99 compiles, the NAN and INFINITY macros expand to these keywords.) Float and long double versions can be created by casting the double ones. The D programming language is even more straightforward: float.nan // represents floating point NaN value float.infinity // represents floating point infinity value double.nan double.infinity // analogous double versions etc. -Walter www.digitalmars.com free C, C++ and D compilers "code of the nerds" Back to top Jon Wilson Guest Posted: Fri Dec 31, 2004 3:56 pm    Post subject: Re: NaN and inf literal constants g++ Victor Bazarov wrote: Quote: "Jon Wilson" <jsw (AT) fnal (DOT) gov> wrote... How do I write Not A Number or +/- infinity (floating point values) as literal constants (I'm using g++)? I have a function that returns float, and I need a flag value, and for various reasons one of NaN, +/-inf would be most convenient. But how do I tell my function to return one of these? The best I can come up with so far is float foo() { if(bar) return (2 + 2); else return (0.0 / 0.0); } Which works, ( (0.0 / 0.0) == NaN, or (1.0 / 0.0) == inf ), but g++ gives me a divide-by-zero warning when I compile. Take a look at std::numeric_limits template, there are static member functions for NaN, infinity, and other things. You won't need to do anything as weird as what you've shown. V Unfortunately, I don't seem to have the std::numeric_limits template... I'm running on FermiLinux, and for some reason, the FermiLinux maintainers are extremely late adopters... I've still got gcc 2.96. And since I would expect any of my users to be running on the same distro, I can't add my own little extensions. cmath includes math.h includes bits/nan.h, but only if __ISO_C99 is defined, which it apparently is not, so I don't have the NAN macro defined. However, I have found HUGE_VAL to be defined, which gives me inf. Thank you! 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