🚀 go-pugleaf

Ethan Henry <ethan@learnix.ca> writes:
>[someone wrote:]
>>>>"Brett W. Denner" <dennerbw@cliffy.lfwc.lockheed.com> writes:
>>>>>Is there a way to identify whether a data type in a template function is a

>>>>>class or a built-in type?  For example,
>>
>>How about using template specialization?
>>	template<class T> bool builtin() { return false; }
>>	template<class T> bool builtin<char>() { return true; }
>
>Why not use RTTI ? typeid() will tell you the info you need...

Perhaps because you want to write standard-conforming, portable code?

>from G++ 2.7.0 typeinfo.h:

If you are interested in writing standard-conforming portable
code, it would be more useful to read the draft standard than
to read your particular implementation's header files.

>public:
>  enum node_type {
>    _RTTI_BUILTIN_TYPE,               // builtin type
>    _RTTI_USER_TYPE,                  // user defined type
>    _RTTI_CLASS_TYPE,                 // class type
>    _RTTI_POINTER_TYPE,               // pointer type
>    _RTTI_ATTR_TYPE,                  // attribute type for const and volatile

>    _RTTI_FUNC_TYPE,                  // function type
>    _RTTI_PTMF_TYPE,                  // pointer to member function type
>    _RTTI_PTMD_TYPE                   // pointer to member data type
>    };
>
>  // return node type of the object
>  virtual node_type __rtti_get_node_type() const {}

Note that all these names (other than `node_type') are in the implementation's
namespace, since they start with two underscores or with an underscore
and a capital letter.  These names are all GNU C++ extensions.

>so to determine the type of object x...
>
>if(typeid(x).__rtti_get_node_type() == _RTTI_BUILTIN_TYPE)
>	cout << "x is a builtin type" << endl;
>else if if(typeid(x).__rtti_get_node_type() == _RTTI_CLASS_TYPE)
>	cout << "x is a class type" << endl;
>etc.

That may work with g++ 2.7, but it is not portable, and it does
not conform to the draft C++ standard.

-- 
Fergus Henderson             	WWW: http://www.cs.mu.oz.au/~fjh
fjh@cs.mu.oz.au              	PGP: finger fjh@128.250.37.3
---
[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
  is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]