C++ Type Properties


Example

C++11

Type properties compare the modifiers that can be placed upon different variables. The usefulness of these type traits is not always obvious.

Note: The example below would only offer an improvement on a non-optimizing compiler. It is a simple a proof of concept, rather than complex example.

e.g. Fast divide by four.

template<typename T>
inline T FastDivideByFour(cont T &var) {
  // Will give an error if the inputted type is not an unsigned integral type.    
  static_assert(std::is_unsigned<T>::value && std::is_integral<T>::value,
    "This function is only designed for unsigned integral types.");
  return (var >> 2);
}

Is Constant:

This will evaluate as true when type is constant.

std::cout << std::is_const<const int>::value << "\n"; // Prints true.
std::cout << std::is_const<int>::value << "\n"; // Prints false.

Is Volatile:

This will evaluate as true when the type is volatile.

std::cout << std::is_volatile<static volatile int>::value << "\n"; // Prints true.
std::cout << std::is_const<const int>::value << "\n"; // Prints false.

Is signed:

This will evaluate as true for all signed types.

std::cout << std::is_signed<int>::value << "\n"; // Prints true.
std::cout << std::is_signed<float>::value << "\n"; // Prints true.
std::cout << std::is_signed<unsigned int>::value << "\n"; // Prints false.
std::cout << std::is_signed<uint8_t>::value << "\n"; // Prints false.

Is Unsigned:

Will evaluate as true for all unsigned types.

std::cout << std::is_unsigned<unsigned int>::value << "\n"; // Prints true.
std::cout << std::is_signed<uint8_t>::value << "\n"; // Prints true.
std::cout << std::is_unsigned<int>::value << "\n"; // Prints false.
std::cout << std::is_signed<float>::value << "\n"; // Prints false.