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  1. #include <iostream>
  2. #include <stdexcept>
  3.  
  4. template<typename T>
  5. constexpr T pack(bool b)
  6. {
  7.     return b;
  8. }
  9.  
  10. template<typename T, typename... Types>
  11. constexpr T pack(bool b, Types... args)
  12. {
  13.     static_assert(std::is_integral<T>::value, "The pack type is not an integral type");
  14.     static_assert(sizeof(T) * 8 >= 1 + sizeof...(Types), "The pack type is not large enough to store the bits you have passed");
  15.     return (b << sizeof...(Types)) | pack<T>(args...);
  16. }
  17.  
  18. template<typename T>
  19. void unpack(T packed, bool& b)
  20. {
  21.     b = packed & 1;
  22. }
  23.  
  24. template<typename T, typename... Types>
  25. void unpack(T packed, bool& b, Types&... args)
  26. {
  27.     static_assert(std::is_integral<T>::value, "The pack type is not an integral type");
  28.     static_assert(sizeof(T) * 8 >= 1 + sizeof...(Types), "The pack type is not large enough to provide the bits you have requested");
  29.     b = packed & (1 << sizeof...(Types));
  30.     unpack(packed, args...);
  31. }
  32.  
  33. template<typename T, typename... Types>
  34. void unpackChecked(T packed, bool& b, Types&... args)
  35. {
  36.     static_assert(std::is_integral<T>::value, "The pack type is not an integral type");
  37.     if(packed >= 1 + sizeof...(Types)) {
  38.     	throw std::overflow_error(__PRETTY_FUNCTION__);
  39.     }
  40.     b = packed & (1 << sizeof...(Types));
  41.     unpack(packed, args...);
  42. }
  43.  
  44. void printPackedUnpacked(int number) {
  45. 	bool b0, b1;
  46. 	unpack(number, b0, b1);
  47. 	std::cout << "The number you entered was:" << pack<int>(b0, b1) << "\n";
  48. }
  49.  
  50. void printPackedUnpackedChecked(int number) {
  51. 	bool b0, b1;
  52. 	unpackChecked(number, b0, b1);
  53. 	std::cout << "The number you entered was:" << pack<int>(b0, b1) << "\n";
  54. }
  55.  
  56. int main() {
  57. 	std::cout << "Enter number: ";
  58. 	int number;
  59. 	std::cin >> number;
  60. 	// Oops: no check if we have enough bits to represent the number
  61. 	printPackedUnpacked(number);
  62. 	//Ok, we check, but what if we decide to only use one bit and forget to 
  63. 	//update the check itself?
  64. 	if(number < (1<<2))
  65. 		printPackedUnpacked(number);
  66. 	// now we don't need to update two places:
  67. 	try {
  68. 		printPackedUnpackedChecked(number);
  69. 	} catch(const std::overflow_error &) {
  70. 		std::cout << "The number you entered was to big to be processed!\n";
  71. 	}
  72. }
Success #stdin #stdout 0s 3480KB
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Enter number: The number you entered was:1
The number you entered was to big to be processed!
https://ideone.com/1R3xlP
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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