#include <iostream>
#include <stdexcept>

using namespace std;

template<typename U>
bool is_big_endian() {
  if (sizeof(U) == sizeof(char)) {
    throw std::logic_error( "big endian versus little endian can only be measured for data types with size greater than the sizeof(char)");
  }
  const int num_bytes = sizeof(U) / sizeof(char);
  union {
    char bytes[num_bytes];
    U x;
  } U_byte_mask;
  U_byte_mask.x = 1;
  if (U_byte_mask.bytes[0] == 1) return false;
  if (U_byte_mask.bytes[num_bytes-1] == 1) return true;
  throw std::logic_error( "this datatype on this machine is neither big endian nor small endian");
}

int main()
{
  bool int_is_bigendian;
  try {
    int_is_bigendian = is_big_endian<int>();
  } catch (exception &e) {
    cerr << e.what() << endl;
    return 1;
  }

  bool long_is_bigendian;
  try {
    long_is_bigendian = is_big_endian<long>();
  } catch (exception &e) {
    cerr << e.what() << endl;
    return 1;
  }

  if (int_is_bigendian) {
    cout << "int's are big endian" << endl;
  } else {
    cout << "int's are small endian" << endl;
  }

  if (long_is_bigendian) {
    cout << "long's are big endian" << endl;
  } else {
    cout << "long's are small endian" << endl;
  }

  return 0;
}

int's are small endian
long's are small endian