[boost] Re: static sized strings (struct hack)

From: John Nagle (nagle_at_[hidden])
Date: 2004-06-12 11:14:16

    I think we're back to using an abstract base class.
The hacks to get around it introduce worse problems.

    Take a look at my approach at

http://www.animats.com/source/index.html

That's a straightforward approach.  The only
fundamental objection is that you take a virtual function
call overhead on some operations.

What needs to be done to that?
Should I check it into the Boost sandbox, and
if so, how?  Comments, please.  Thanks.

                        John Nagle
                        Animats

Bill Seymour wrote:

> Rob Stewart:
> 
>>From: John Nagle <nagle_at_[hidden]>
>>
>>>>From: "Reece Dunn" <msclrhd_at_[hidden]>
>>>
>>>>>  class fs_base
>>>>>  {
>>>>>     size_t len;
>>>>>     szie_t capacity; // needed for buffer-safe operations
>>>>>     CharT str[ 1 ];
>>>>>     // string manipulation functions
>>>>>
>>>>>     fs_base( size_t c ): capacity( c ){}
>>>>>  };
>>>>>
>>>>>  template< size_t n >
>>>>>  class fixed_string: public fs_base
>>>>>  {
>>>>>     CharT data[ n ];
>>>>>     fixed_string(): fs_base( n ){}
>>>>>  };
>>>
>>>     Are you assuming that "data[n]" physically follows
>>>"str[1]" in memory, and that "data[n]" can be addressed
>>>by subscripting "str[1]" out of range? ...
>>
>>Oh, right.  It was C99 that blessed the struct hack.  Oh well.
>>
> 
> 
> Well, yes; but the struct hack is not what the code above
> tries to do.  What C99 says is that you can malloc sizeof(fs_base)
> plus some extra, then address str[2] to str[whatever up to
> malloc'd size].  Even in C99 (and even if C understood the
> C++-specific stuff in the above), there is no relationship
> between fs_base::str and fixed_string::data (except that
> they don't overlap).
> 
> --Bill Seymour
> _______________________________________________
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
>