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the problem of gettimeofday

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Top Forums Programming the problem of gettimeofday
# 8  
Old 08-04-2008
Quote:
Originally Posted by dophine
let us take this "Big:1217489802.1217489802,1217485404.813903,4398.000000" as an example.
1217489802-1217485404=4398

so, there are some problems for the difftime function?
What do you mean by "problems with the difftime function" Smilie
The difference between the programmatically and manually computed times is correct and your printf() doesn't have the microsecond counter so I added it in.

Code:
printf("Big:%ld.%ld,%ld.%ld,%lf\n",new_time.tv_sec,new_time.tv_usec, cur.tv_sec,cur.tv_usec,diff);

What do you get if you just subtract cur.tv_usec from new_time.tv_usec without calling difftime().

Code:
diff = new_time.tv_usec - cur.tv_usec;

# 9  
Old 08-04-2008
Quote:
Originally Posted by shamrock
What do you mean by "problems with the difftime function" Smilie
The difference between the programmatically and manually computed times is correct and your printf() doesn't have the microsecond counter so I added it in.
just forget this.

Quote:
Originally Posted by shamrock
Code:
printf("Big:%ld.%ld,%ld.%ld,%lf\n",new_time.tv_sec,new_time.tv_usec, cur.tv_sec,cur.tv_usec,diff);

What do you get if you just subtract cur.tv_usec from new_time.tv_usec without calling difftime().

Code:
diff = new_time.tv_usec - cur.tv_usec;

As I expect the time does not go back or forward by more 1 second, the micro second part is not my concern. the same result occurs suing subtraction directly. So I suspect there is a problem for gettimeofday.
# 10  
Old 08-05-2008
What platform are you on...cast the null pointer correctly in your call to gettimeofday() and see if that affects the result.

Code:
gettimeofday(&cur, (void *)0);

# 11  
Old 08-05-2008
red hat in a multi-cores platform.

it said invalid conversion from `void*' to `timezone*'.
if I change to gettimeofday(&cur, (timezone *)0); it said "expected primary-expression before ')' token"
# 12  
Old 08-05-2008
Quote:
Originally Posted by dophine
Here is the result:
Small::1217485404.98014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.99014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.100014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.101013,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.102014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.103014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.104014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.105014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.106014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.107013,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.108013,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.109013,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.110014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.111014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.112014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.113014,1217489802.813903,-4398.000000
Big:1217489802.1217489802,1217485404.813903,4398.000000
Small::1217485404.114014,1217489802.813903,-4398.000000
You are alternating between two values:
1217485404
1217489802

It looks like the first two calls to gettimeofday() worked and then it started failing. I can't say why, but I certainly don't understand why you are blaming a multi-core environment. System calls return -1 and set errno when they fail. Checking that is the documented way to discover the reason for the failure.
# 13  
Old 08-06-2008
I agree with Perderabo and great catch by the way. I didn't pay attention to the data but it is not incrementing the gettimeofday() output as it should so looks like that call is failing. You need to check the return value from gettimeofday() to make sure it is working correctly.
# 14  
Old 08-06-2008
I have checked it. It always returns 0.
the reason why I said it may be the problem of multi-core is I found this website
linux-kernel - gettimeofday() jumping into the future
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