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  1. #include <cstdio>
  2. using namespace std;
  3.  
  4. int main(void)
  5. {
  6. 	double *d = new double; 
  7. 	*d = 15.25; 
  8. 	printf("float: %f\n", *d);
  9.  
  10. 	//forced hex output of double
  11. 	printf("forced bitwise of double: ");
  12. 	unsigned char * c = (unsigned char *) d;
  13. 	int i;
  14. 	for (i = sizeof (double)-1; i >=0 ; i--) {
  15. 	     printf ("%02X ", c[i]);
  16. 	}
  17. 	printf ("\n");
  18.  
  19. 	//cast to long long-pointer, so that bitops become possible
  20. 	long long * l = (long long*)d;
  21. 	//now the bitops: 
  22. 	printf("IntHex: %016X, float: %f\n", *l, *(double*)l); //this output is wrong!
  23. 	*l = *l | 0x07; 
  24. 	printf("last 3 bits set to 1: %016llX, float: %.30f\n", *l, *d);//this output is wrong!
  25. 	*l = *l | 0x18; 
  26. 	printf("2 bits more set to 1: %016llX, float: %.30f\n", *l, *d);//this output is wrong!
  27.  
  28. 	*l = *l | 0x10000000000ll;
  29. 	printf("float4: %f\n", *d);
  30. }
  31.  
Success #stdin #stdout 0.01s 2856KB
comments (?)
stdin 
Standard input is empty
stdout 
float: 15.250000
forced bitwise of double: 40 2E 80 00 00 00 00 00 
IntHex: 0000000000000000, float: 0.000000
last 3 bits set to 1: 402E800000000007, float: 15.250000000000012434497875801753
2 bits more set to 1: 402E80000000001F, float: 15.250000000000055067062021407764
float4: 15.251953
https://ideone.com/1MgiQ
language:
C++ (gcc 8.3)
created:
13 years ago
visibility:
public

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