[Libpqxx-general] distance() return type

[Jorgen Austvik - Sun Norway]

Hi,

in include/pqxx/compiler-internal.hxx, the distance function is defined 
like this:

----8<-----------8<-----------8<-----------8<-----------8<-----------8<-------
/// Wrapper for std::distance; not all platforms have std::distance().
template<typename T> inline ptrdiff_t distance(T first, T last)
{
#ifdef PQXX_HAVE_DISTANCE
   return PGSTD::distance(first, last);
#else
   // Naive implementation.  All we really need for now.
   iterator_traits<T>::difference_type d = 0;
   while (first != last) ++d;
   return d;
#endif
}
----8<-----------8<-----------8<-----------8<-----------8<-----------8<-------

I am curious why the return type of the function is ptrdiff_t while it 
looks like std::distance returns iterator_traits<T>::difference_type[1], 
and the d variable certainly has that type - should they all be 
iterator_traits<T>::difference_type?

On the Sun Studio compiler, with it's Rough Wave STL implementation, 
iterator_traits does not exist (and std::distance is also non-standard). 
There I just change iterator_traits<T>::difference_type d = 0 to 
ptrdiff_t d = 0, which seems to do the job there.

[1] http://www.sgi.com/tech/stl/distance.html
[2] http://wikis.sun.com/pages/viewpage.action?pageId=6455548

-J
-- 

Jørgen Austvik, Software Engineering - QA
Sun Microsystems Database Group

http://blogs.sun.com/austvik/
http://www.austvik.net/