Re: Private inheritance from std::basic_string

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.stl

Date:

Fri, 8 Jan 2010 17:02:46 -0500

Message-ID:

<eEbBR5KkKHA.1864@TK2MSFTNGP05.phx.gbl>

Praetorian <ashish.sadanandan@gmail.com> wrote:

This is what the class looks like so far:

class string_t :
#if defined(UNICODE) || defined(_UNICODE)
private std::basic_string<wchar_t>
#else
private std::basic_string<char>
#endif

Consider using basic_string<TCHAR> - it works without ifdefs.

{
public:
string_t() : basic_string<value_type>() {}

string_t( const basic_string<value_type>& str )
   : basic_string<value_type>( str ) {}

virtual ~string_t() {}

using std::basic_string<value_type>::operator=; /* Line causing
error */

std::vector<string_t> split( const string_t& delims )
{
   std::vector<string_t> tokens;

   tokens.push_back( substr( 0, npos ) );
}
};
I get the following errors:

1>c:\program files\microsoft visual studio 9.0\vc\include\xutility
(3133) : error C2243: 'type cast' : conversion from 'const string_t *'
to 'const std::basic_string<_Elem,_Traits,_Ax> &' exists, but is
inaccessible 1> with 1> [ 1> _Elem=wchar_t, 1>
_Traits=std::char_traits, 1> _Ax=std::allocator 1> ]

vector requires that its value type be assignable. To work in a vector, =
string_t should provide an assignment operator taking const string_t&.

Without that using directive, the compiler generated a default =
assignment operator for you. But by bringing other declarations into =
your class, you suppressed that.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not =
necessarily a good idea. It is hard to be sure where they are going to =
land, and it could be dangerous sitting under them as they fly overhead. =
-- RFC 1925