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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)
  18. 	, num_2(2)
  19. 	, num_3(3)
  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. 	void* const pFirst = static_cast<void*>(&pObj->num_1);
  36. 	void* const pLast = static_cast<void*>(&pObj->num_3);
  37.  
  38. 	const ptrdiff_t delta = static_cast<char*>(pLast) - static_cast<char*>(pFirst);
  39. 	assert(delta > 0);
  40. 	std::cout << "delta =  " << delta << "\n";
  41. 	const size_t sizeAll = delta + sizeof(int);
  42. 	std::cout << "sizeAll =  " << sizeAll << "\n";
  43.  
  44. 	std::vector<char> buf( sizeAll, 0 );
  45. 	memcpy(pFirst, &buf[0], sizeAll);
  46. }
  47.  
  48. int main()
  49. {
  50. 	MyStandardLayout obj;
  51. 	obj.print();
  52. 	ZeroInts(&obj);
  53. 	obj.print();
  54.  
  55.     return 0;
  56. }
  57.  
  58.  
Success #stdin #stdout 0s 3468KB
comments (?)
stdin 
Standard input is empty
stdout 
MySL Obj: a / 1 / 2 / 3 / z
delta =  6
sizeAll =  10
MySL Obj: a / 0 / 0 / 0 / z
https://ideone.com/1lP2Gd
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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