literalcategory.cpp

#include <iostream>

template<typename T>
struct value_category {
  static constexpr auto value = "prvalue";
};
template<typename T>
struct value_category<T&> {
  static constexpr auto value = "lvalue";
};
template<typename T>
struct value_category<T&&> {
  static constexpr auto value = "xvalue";
};
#define VALUE_CATEGORY(expr) value_category<decltype((expr))>::value

// UDL
struct X {};
X operator "" _x(unsigned long long) { return {}; }

int main()
{
  std::cout << VALUE_CATEGORY(42)      << std::endl;  // integer-literal
  std::cout << VALUE_CATEGORY('X')     << std::endl;  // character-literal
  std::cout << VALUE_CATEGORY(3.14)    << std::endl;  // floating-literal
  std::cout << VALUE_CATEGORY("ABC")   << std::endl;  // string-literal
  std::cout << VALUE_CATEGORY(true)    << std::endl;  // boolean-literal
  std::cout << VALUE_CATEGORY(nullptr) << std::endl;  // pointer-literal
  std::cout << VALUE_CATEGORY(1_x)     << std::endl;  // user-defined-literal
}