Re: [boost] Interest in a small array count facility?

From: Matt Calabrese (rivorus_at_[hidden])
Date: 2006-06-25 13:59:57

On 6/25/06, me22 <me22.ca_at_[hidden]> wrote:
>
> I think it's worth including.  It's not all that uncommon; even
> Freenode/##C++'s channel bot has the following factoid:
> Don't use sizeof() to get the size of an array, because sizeof() will
> do the wrong thing if that 'array' is actually a pointer.  Use the
> following instead: template <typename T, size_t N> size_t array_size(T
> (&)[N]) { return N; }

The downside of that is that it doesn't yield a compile-time constant, so
you can't use it, for instance, as the size of another non-dynamically
allocated array, nor for template metaprogramming, etc. For my projects, I
do something like:

#include <cstddef>

namespace boost
{
template< typename Type, ::std::size_t Size >
char (&array_size_impl( Type (&)[Size] ))[Size];
}

#define BOOST_ARRAY_SIZE( array ) sizeof( ::boost::array_size_impl( array )
)

////////////////////////

The benefit of the above is that in addition to
giving an easy-to-read compile-time an
error when attempting to pass a pointer, it also yields a compile-time
constant value.

-- 
-Matt Calabrese