How to check type on compile time

Question

I'm giving option to compile the program with either float or double type, but there is a problem: I need to manually set either GL_FLOAT or GL_DOUBLE, because I dont know how can I do the following:

typedef float MYTYPE;

#if MYTYPE == float
    #define GL_MYTYPE GL_FLOAT // used for vertex array parameters.
#else
    #define GL_MYTYPE GL_DOUBLE
#endif

Note: I dont have C++11 or whatsoever, just the good old C++.

Answer 1

In C++11, you can use std::conditional and std::is_same as:

#define GL_MYTYPE  std::conditional                       \
                   <  std::is_same<MYTYPE,float>::value,  \
                      GL_FLOAT,                           \
                      GL_DOUBLE                           \
                   >::type                            

In C++03, you can implement these functionalities yourself as:

template<bool B, class T, class F>
struct conditional { typedef T type; };

template<class T, class F>
struct conditional<false, T, F> { typedef F type; };

and

template<class T, class U>
struct is_same { static const bool value = false; };

template<class T>
struct is_same<T, T> { static const bool value = true; };

Note that the implementation of conditional is taken from the site itself.