Fun with gettimeofday

This is a discussion on Fun with gettimeofday within the Linux Programming forums, part of the Platform Specific Boards category; The tv_usec field in struct timeval is supposed to store the number of microseconds since January 1, 1970 00:00. But ...

  1. #1
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    Fun with gettimeofday

    The tv_usec field in struct timeval is supposed to store the number of microseconds since January 1, 1970 00:00. But when I do the following:
    Code:
    #include <sys/time.h>
    
    int main()
    {
    	int i;
    	struct timeval start, end;
    	struct timezone tzp;
    
    	gettimeofday(&start, &tzp);
    
    	for(i = 0; i < 100000; i++){}
    	
    	gettimeofday(&end, &tzp);
    
    	printf("start: %lu\n", start.tv_usec);
    	printf("end: %lu\n", end.tv_usec);
    	printf("time: %lu\n", end.tv_usec - start.tv_usec);
    
    	return 0;
    }
    The values I get for start.tv_usec and end.tv_usec are not increasing after every run of the program. For example, I'll get
    start: 609659
    end: 610257

    and in another run afterwards I'll get
    start: 204615
    end: 205695

  2. #2
    and the hat of wrongness Salem's Avatar
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    > The tv_usec field in struct timeval is supposed to store the number of microseconds since January 1, 1970 00:00
    No, tv_sec stores this value

    tv_usec is 0 to 999999

    If tv_usec is 999999, adding 1 resets it back to 0, and increments tv_sec
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    Thanks

    Thanks. You're a pro.

  4. #4
    Registered User newbie_grg's Avatar
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    haha..

    Believe me dude Salem is the only REAL programmer we have in this forum...
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    -Isaac Asimov(1920-1992)

  5. #5
    Comment your source code! Lynux-Penguin's Avatar
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    I don't know I think Prelude, and Hammer classify as programmers too.

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  6. #6
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    Originally posted by Lynux-Penguin
    I don't know I think Prelude, and Hammer classify as programmers too.

    -LC
    But aren't we all?
    Sigh, nothing ever works the first try.

    Register Linux User #314127

  7. #7
    twm
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    >But aren't we all?
    I'm not. And proud of it too. Programmers are always running around mumbling about deadlines and looking worried. I run around making deadlines and looking goofy. That's the way to live life!
    The information given in this message is known to work on FreeBSD 4.8 STABLE.
    *The above statement is false if I was too lazy to test it.*
    Please take note that I am not a technical writer, nor do I care to become one.
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    Don't assume that I'm ever entirely serious or entirely joking.

  8. #8
    still a n00b Jaguar's Avatar
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    I agree with you all.
    But where is vVv and where are his posts?
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