Question

#include <stdio.h>
#include <unistd.h>
int main()
{
    while(1)
    {
        fprintf(stdout,"hello-out");
        fprintf(stderr,"hello-err");
        sleep(1);
    }
    return 0;
}

The output of above on my machine is

hello-errhello-errhello-errhello-errhello-errhello-errhello-errhello-errhello-errhello-errhello-errhello-errhello-errhello-err

I had to kill the program to stop it.
Is it the correct and expected behavior.
Or it is wrong.This was an interview question hence I am posting here.

Answer 1

This is the expected output:

• The program loops forever because of the while (1) loop.
• stdout is line-buffered (by default), so it only flushes to the console when a new-line character ('\n') is printed. As you aren’t printing any new-line characters, you never see any of the hello-out text.
• However stderr is not line-buffered (by default), so it updates the console on every new fprintf() call.