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  1. #include <vector>
  2. #include <iostream>
  3. #include <assert.h>
  4. #include <inttypes.h>
  5. #include <stddef.h>
  6. #include <memory.h>
  7.  
  8. struct MyStandardLayout {
  9. 	char mem_a;
  10. 	int16_t num_1;
  11. 	int32_t num_2;
  12. 	int64_t num_3;
  13. 	char mem_z;
  14.  
  15. 	MyStandardLayout()
  16. 	: mem_a('a')
  17. 	, num_1(1 + (1 << 14))
  18. 	, num_2(1 + (1 << 30))
  19. 	, num_3(1LL + (1LL << 62))
  20. 	, mem_z('z')
  21. 	{ }
  22.  
  23. 	void print() const {
  24. 		std::cout << 
  25. 			"MySL Obj: " <<
  26. 			mem_a << " / " <<
  27. 			num_1 << " / " <<
  28. 			num_2 << " / " <<
  29. 			num_3 << " / " <<
  30. 			mem_z << "\n";
  31. 	}
  32. };
  33.  
  34. void ZeroInts(MyStandardLayout* pObj) {
  35. 	const size_t first = offsetof(MyStandardLayout, num_1);
  36. 	const size_t third = offsetof(MyStandardLayout, num_3);
  37. 	std::cout << "ofs(1st) =  " << first << "\n";
  38. 	std::cout << "ofs(3rd) =  " << third << "\n";
  39. 	assert(third > first);
  40. 	const size_t delta = third - first;
  41. 	std::cout << "delta =  " << delta << "\n";
  42. 	const size_t sizeAll = delta + sizeof(MyStandardLayout::num_3);
  43. 	std::cout << "sizeAll =  " << sizeAll << "\n";
  44.  
  45. 	std::vector<char> buf( sizeAll, 0 );
  46. 	memcpy(&pObj->num_1, &buf[0], sizeAll);
  47. }
  48.  
  49. int main()
  50. {
  51. 	MyStandardLayout obj;
  52. 	obj.print();
  53. 	ZeroInts(&obj);
  54. 	obj.print();
  55.  
  56.     return 0;
  57. }
  58.  
  59.  
Success #stdin #stdout 0s 3468KB
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stdin
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Standard input is empty
stdout
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MySL Obj: a / 16385 / 1073741825 / 4611686018427387905 / z
ofs(1st) =  2
ofs(3rd) =  8
delta =  6
sizeAll =  14
MySL Obj: a / 0 / 0 / 0 / z
https://ideone.com/YXspBk
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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