Re: [boost] Question about leading underscores

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2001-06-22 17:40:28

From: <rwgk_at_[hidden]>
> In the header file boost/utility.hpp, leading underscores are
> are used for some variable names:
> 
>     template <class A, class B>
>     class tied {
>     public:
>       inline tied(A& a, B& b) : _a(a), _b(b) { }
>       /...
>     protected:
>       A& _a;
>       B& _b;
>     };
> 
> I always thought that identifiers with leading underscores
> should not be used. Is this only true for identifieres
> in the global namespace?

The safe rule is not to use leading underscores, although I
think those above are technically OK, if useless.

17.4.3.1.2  Global names                            [lib.global.names]

1 Certain sets of names and function signatures are always  reserved  to
  the implementation:

  --Each  name  that  contains a double underscore __) or begins with an
    underscore followed by an uppercase letter (_lex.key_)  is  reserved
    to the implementation for any use.

  --Each  name  that begins with an underscore is reserved to the imple-
    mentation for use as a name in the global namespace.22)

  _________________________
  22)  Such  names  are  also  reserved  in  namespace  ::std  (_lib.re-
  served.names_).