Possible Duplicate:
Is there an easy way to tell if a class/struct has no data members?
Can we detect emply classes, possibly using template?
struct A {};
struct B { char c;};
std::cout << is_empty<A>::value; //should print 0
std::cout << is_empty<B>::value; //should print 1
//this is important, the alleged duplicate doesn't deal with this case!
std::cout << is_empty<int>::value; //should print 0
Only C++03 only, not C++0x!
If your compiler supports the empty base class optimization, yes.
template <typename T>
struct is_empty
{
struct test : T { char c; };
enum { value = sizeof (test) == sizeof (char) };
};
template <>
struct is_empty<int>
{
enum { value = 0 };
};
Better:
#include <boost/type_traits/is_fundamental.hpp>
template <bool fund, typename T>
struct is_empty_helper
{
enum { value = 0 };
};
template <typename T>
struct is_empty_helper<false, T>
{
struct test : T { char c; };
enum { value = sizeof (test) == sizeof (char) };
};
template<typename T>
struct is_empty
{
enum { value = is_empty_helper<boost::is_fundamental<T>::value, T>::value };
};