Weird behaviour of nanosleep() in a loop

Asked May 01 '20 at 17:49

Active May 01 '20 at 17:56

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I was writing a simple C program, then I ran to a problem: when I put nanosleep() in a loop, my output is different from what I expect. The code is simple:

struct timespec ts = {1, 0};
    for(int i = 0; i<4; i++)
    {
      printf("test ");
      nanosleep(&ts,NULL);
    }

From what I understand, it should print word "test", then wait 1 second, repeat. However, when I run it, it waits for 4 seconds, and then it prints "test" four times, immediately. What confuses me the most, is that the printing of each word should be done before sleeping, but it seems like it doesn't happen even in the first iteration of the loop. I realize that it may not be correct use of nanosleep() but in man nanosleep I couldn't find anything about not using it in loops.

asked May 01 '20 at 17:49

Jakub Malinowski

3

Output buffering. Append a newline, or `fflush`. – Eugene Sh. May 01 '20 at 17:50
Need to find a canonical dupe for this – Barmar May 01 '20 at 17:51
There is some good information on this topic [here](https://eklitzke.org/stdout-buffering). – larsks May 01 '20 at 17:51
This has nothing to do with nanosleep or loops. Any long-running function will cause the behavior. – Ben Voigt May 01 '20 at 17:51

Weird behaviour of nanosleep() in a loop

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