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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <cstring>
  4. #include <typeinfo>
  5.  
  6. using namespace std;
  7.  
  8. template <size_t O,size_t I,size_t C,typename...>
  9. struct byte_offset_impl;
  10.  
  11. template <size_t O,size_t I,size_t C,typename T,typename... Ts>
  12. struct byte_offset_impl< O, I, C,T,Ts...> : 
  13. 	std::conditional<I == C,
  14. 	  std::integral_constant<size_t,O>,
  15. 	  byte_offset_impl<O + sizeof(T),I,C+1,Ts...>	 
  16. 	>::type
  17. {};
  18.  
  19.  
  20. template <typename T>
  21. struct type_c 
  22. { using type = T; };
  23.  
  24. template <size_t I,size_t C,typename...>
  25. struct type_at_impl;
  26.  
  27. template <size_t I,size_t C,typename T,typename... Ts>
  28. struct type_at_impl<I, C,T,Ts...> : 
  29. 	std::conditional<I == C,
  30. 	  type_c<T>,
  31. 	  type_at_impl<I,C+1,Ts...>	 
  32. 	>::type
  33. {};
  34.  
  35.  
  36. template <size_t I,typename... Ts>
  37. constexpr size_t byte_offset = byte_offset_impl<0,I,0,Ts...>::value;
  38.  
  39. template <size_t I,typename... Ts>
  40. using type_at = typename type_at_impl<I,0,Ts...>::type;
  41.  
  42. template <typename...Ts>
  43. struct generic_class
  44. {
  45. 	generic_class(char* byteptr) : byteptr_(byteptr)
  46. 	{};
  47.  
  48.  
  49. 	template <size_t I>
  50. 	auto get() -> type_at<I, Ts...>& // needed for c++11
  51. 	{
  52. 		using result_type = type_at<I, Ts...>;
  53. 		return *reinterpret_cast<result_type*>(&byteptr_[byte_offset<I, Ts...>]);
  54.  
  55. 	}
  56.  
  57. 	template <size_t I>
  58. 	auto get_v() -> type_at<I, Ts...> // needed for c++11
  59. 	{
  60. 		using result_type = type_at<I, Ts...>;
  61. 		result_type result;
  62.  
  63. 		std::memcpy(&result, &byteptr_[byte_offset<I, Ts...>], sizeof(result_type));
  64.  
  65. 		return result;
  66. 	}
  67. 	char* byteptr_;
  68. };
  69.  
  70.  
  71. int main() {
  72.  
  73. 	char bytes[sizeof(uint32_t) + sizeof(uint8_t) + sizeof(uint16_t)];
  74.  
  75. 	uint32_t u32 = 1561;
  76. 	uint8_t u8 = 22;
  77. 	uint16_t u16 = 99;
  78.  
  79. 	char* bytesp = bytes;
  80. 	std::memcpy(bytesp, &u32, sizeof(uint32_t)); bytesp += sizeof(uint32_t);
  81. 	std::memcpy(bytesp, &u8, sizeof(uint8_t)); bytesp += sizeof(uint8_t);
  82. 	std::memcpy(bytesp, &u16, sizeof(uint16_t));
  83.  
  84. 	generic_class<uint32_t, uint8_t, uint16_t> gen(bytes);
  85. 	std::cout << (uint32_t)gen.get<0>() << std::endl;
  86. 	std::cout << (uint32_t)gen.get<1>() << std::endl;
  87. 	std::cout << (uint32_t)gen.get<2>() << std::endl;
  88.  
  89. 	std::cout << (uint32_t)gen.get_v<0>() << std::endl;
  90. 	std::cout << (uint32_t)gen.get_v<1>() << std::endl;
  91. 	std::cout << (uint32_t)gen.get_v<2>() << std::endl;
  92. }
Success #stdin #stdout 0s 4304KB
comments (?)
stdin
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Standard input is empty
stdout
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1561
22
99
1561
22
99
https://ideone.com/xvbSUN
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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