double类型变量的奇怪值：-nan（0x8000000000000） [英] Strange value of the double type variable: -nan(0x8000000000000)

问题描述

添加操作后，我对currdisk-> currangle的值感到困惑。最初currdisk-> currangle的值是0.77500000000000013，但是在添加操作之后，它改为-nan（0x8000000000000），有人可以解释一下吗？谢谢！以下是gdb调试的场合。

  3338  currdisk-> currangle + =（simtime  - seg-> time; / currdisk-> rotatetime; 
（gdb）p currdisk-> currangle 
 $ 28 =  0 。 77500000000000013  
（gdb）p（simtime  -  seg-> time）/ currdisk-> rotatetime 
 $ 29 =  0 。 00833333333333325  
（gdb）p（simtime  -  seg->时间）
 $ 30 =  0 。< span class =code-digit> 092592592592591672  
（gdb）p currdisk-> rotatetime 
 $ 31 =  11 。< span class =code-digit> 111111111111111  
（gdb）n 
 
（gdb）p currdisk-> currangle 
 $ 32 = -nan（0x8000000000000） 
（gdb）p / x（ char  [ 8 ]）currdisk-> currangle 
 $ 52 = {0x0,0x0,0x0,0x0,0x0,0x0,0xf8,0xff} 
（gdb）

然后我改变

 currdisk-> currangle + =（simtime  -  seg-> time）/ currdisk-> rotatetime; 

to

  double  tmp1 =（ simtime  -  seg-> time）/ currdisk-> rotatetime; 
 currdisk-> currangle + = tmp1; 

currdisk-> currangle的值是正常的。任何人都可以解释这个令人困惑的现象吗？

解决方案

28 = 0 。 77500000000000013
（gdb）p（simtime - seg->时间）/ currdisk-> rotatetime

29 = 0 。 00833333333333325
（gdb）p（simtime - seg-> time）

< blockquote> 30 = 0 。 092592592592591672
（gdb）p currdisk-> rotatetime

I am confused by the value of "currdisk->currangle" after adding operation. Initially the value of "currdisk->currangle" is 0.77500000000000013, but after adding operation, it's changed to "-nan(0x8000000000000)", Can anyone explain ? Thanks! The following is the occasion of gdb debugging.

3338          currdisk->currangle += (simtime - seg->time) / currdisk->rotatetime;
(gdb) p currdisk->currangle
$28 = 0.77500000000000013
(gdb) p (simtime - seg->time) / currdisk->rotatetime
$29 = 0.00833333333333325
(gdb) p (simtime - seg->time) 
$30 = 0.092592592592591672
(gdb) p currdisk->rotatetime
$31 = 11.111111111111111
(gdb) n

(gdb) p currdisk->currangle 
$32 = -nan(0x8000000000000)
(gdb) p/x (char[8])currdisk->currangle 
$52 = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xf8, 0xff}
(gdb)

Then I change

currdisk->currangle += (simtime - seg->time) / currdisk->rotatetime ; 

to

double tmp1 = (simtime - seg->time) / currdisk->rotatetime; 
currdisk->currangle += tmp1; 

The value of currdisk->currangle is normal. Can anyone explain the confusing phenomenon ?

解决方案

28 = 0.77500000000000013 (gdb) p (simtime - seg->time) / currdisk->rotatetime

29 = 0.00833333333333325 (gdb) p (simtime - seg->time)

30 = 0.092592592592591672 (gdb) p currdisk->rotatetime

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