Re: [boost] [type_traits] warning free is_signed on g++

Subject: Re: [boost] [type_traits] warning free is_signed on g++
From: John Maddock (john_at_[hidden])
Date: 2009-09-18 06:35:15

> When using boost::is_signed<> on types such as unsigned int and unsigned 
> long,
> various recent versions of g++ (MinGW 4.4.0 and Apple's 4.0.1, at least) 
> spit
> out a warning:
>
>   warning: comparison of unsigned expression < 0 is always false
>
> Would there be any harm in changing boost::detail::is_signed_helper in
> boost/type_traits/is_signed.hpp as follows?
>
>   template <class T>
>   struct is_signed_helper
>   {
>      typedef typename remove_cv<T>::type no_cv_t;
>      // BOOST_STATIC_CONSTANT(bool, value = (static_cast<no_cv_t>(-1) < 
> 0));
>      BOOST_STATIC_CONSTANT(bool, value = (static_cast<no_cv_t>(-1) < 1));
>   };
>
> This change gets rid of the warnings emitted by g++.

Already been there and fixed it: 
https://svn.boost.org/trac/boost/ticket/3381

John.