How to know if the argument that is passed to the function is a class, union or enum in c++?

Question

I want to define an operator<< for all enums, to cout the value and print that it is an enum like this:

code:

enum AnyEnum{A,B,C};
AnyEnum enm          


        

Answer 1

I am interested how to identify if the veriable is a class type, union type or an enum (in compile time).

boost::type_traits

Even C++ TR1 has got a header to support that functionality. In C++0x everything's gonna be a lot better.

For example the following machinery makes use of SFINAE to check whether the argument passed is a class type:

templatestruct Check_If_T_Is_Class_Type
{
    template static char func (char C::*p);
    template static long func (...);
    enum{val = CHECKER(func,Check_If_T_Is_Class_Type)};
};

The MACRO CHECKER is

#define CHECKER(func_name,class_name) \
sizeof(class_name::template func_name(0)) == 1

To understand how type_traits work you need to have some basic knowledge of templates including template metaprogramming and SFINAE.