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  1. #include <iostream>
  2. #include <string>
  3. #include <iomanip>
  4. #include <cstring>
  5. using namespace std;
  6.  
  7. bool is_aligned (char *p) {
  8. 	return reinterpret_cast<unsigned long long>(p)%alignof(int)==0;
  9. }
  10. void dump(const string &message, char *p, size_t s) {
  11. 	cout << message << hex; 
  12. 	for (int i=0; i<s; i++) cout<< (int) p[i]<<" "; cout<<endl;
  13. 	cout<<dec; 
  14. }
  15.  
  16. int main() {
  17. 	int x = 27; 
  18. 	char w;
  19. 	char z [sizeof(int)*10+1];
  20. 	char y; 
  21.  
  22. 	// check conditions 
  23.  
  24. 	cout << " "<< alignof(x) << " "<< alignof(y) << " "<< alignof(z)<<endl; 
  25. 	cout << " "<< &x << " "<< (void*)&y << " "<< (void*) z<<endl; 
  26. 	char *p = z + is_aligned(z);    // never aligned unless int is aligned on 1
  27. 	cout << "Is z aligned for int ? " << (is_aligned(z) ?"yes":"no") <<endl;
  28. 	cout << "Is p aligned for int ? " << (is_aligned(p) ?"yes":"no") <<endl;
  29.  
  30. 	// memcpy option 
  31. 	memcpy (p, &x, sizeof(x)); // test
  32. 	dump ("Int stored with memcpy: ", p, sizeof(int));  
  33. 	x=0; 
  34. 	memcpy (&x,p, sizeof(x)); 
  35. 	memset(p, 0, sizeof (x));	
  36. 	cout << "restored: "<<x<<endl; 
  37.  
  38. 	// reinterpret cast option: 
  39. 	cout << "Going to store with reinterpret cast."<<endl; 
  40. 	*reinterpret_cast<int*>(p) = x;   //ouch 
  41. 	dump ("Int stored with reinterpret cast: ", p, sizeof(int));  
  42. 	x=0; 
  43. 	cout << "Going to restore with reinterpret cast."<<endl; 
  44. 	x = *reinterpret_cast<int const*>( p );
  45. 	cout << "restored: "<<x<<endl; 
  46.  
  47. 	return 0;
  48. }
Success #stdin #stdout 0.01s 5280KB
comments (?)
stdin
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Standard input is empty
stdout
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 4 1 1
 0x7ffc5f25455c 0x7ffc5f25455b 0x7ffc5f254580
Is z aligned for int ? yes
Is p aligned for int ? no
Int stored with memcpy: 1b 0 0 0 
restored: 27
Going to store with reinterpret cast.
Int stored with reinterpret cast: 1b 0 0 0 
Going to restore with reinterpret cast.
restored: 27
https://ideone.com/uiF53Q
language:
C++14 (gcc 8.3)
created:
306 days ago
visibility:
secret

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