sleep() function does not work as expected

Question

I have written a simple code to understand the working of sleep() function in c.

Code:

int main()
{
FILE *fp;
fp=fopen("ass1q1.txt","r");
printf("before sleep");
sleep(5);
printf("\nafter");

}

O/p:

$ ./a.out
before sleep
after

It sleeps for 5 secs & later displays before & after msg together.

Can anyone explain how can I make it work?

Answer 1

Your sleep function is working perfectly. It's just that the output is flushed to screen at the end of the program.

Here's how things are happening :-

1) put "before sleep" string in output buffer

2) sleep for 5 seconds

3) put "\nafter" string in output buffer.

The output buffer is then flushed to stdout after the program execution ( or before if it fills completely )

Try using "fflush(stdout)" after first print statement to flush the output buffer before and see the difference.

Answer 2

I am running it on Ubuntu (via VMware)
Headers used are:

#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>

Answer 3

Thank you for your quick response!
Much appreciated!

Answer 4

Ok ✌

Answer 5

You need to flush output buffer
This normally happens in Linux OS.

Use fflush(stdout) after printing first string