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

From: Bill Seymour (bill-at-the-office_at_[hidden])
Date: 2004-06-07 07:00:01

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