[boost] Re: Problem with type_with_alignment.hpp

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2003-09-03 14:32:02

Hartmut Kaiser wrote:
> Daniel Frey wrote:
> 
> Concatenating two tokens with the '##' operator, where the result isn't
> a new valid token results in undefined behaviour. In your sample it
> yields '>>', which is a valid token, so it is well defined. In other
> contexts two consecutive '>' characters are always interpreted as '>>'
> and not as two single '>'.

That wasn't my point :)

> But this isn't the point here. The '>>' was not formend by a '##'
> operator but by plain consecutiveness:
> 
> #define SOME_MACRO(T)  <T>
> SOME_MACRO(some_class<...>)  // expands to <some_class<...>>

Exactly. But the expanded <some_class<...>> is the result of the 
preprocessor, so IIRC the two >'s are treated as two tokens, not as one, 
because they weren't glued together with ##. Also, the GCC preprocessor 
expands the above to

< some_class<...> >

and I'm pretty sure that the rules for inserting spaces are exactly 
defined and there is not much room for interpretation. If the GCC is 
correct to insert spaces, then the patch is a work-around for a compiler 
(here: preprocessor) bug. So, what is the correct behaviour here?

Regards, Daniel

-- 
Daniel Frey
aixigo AG - financial training, research and technology
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eMail: daniel.frey_at_[hidden], web: http://www.aixigo.de