Running fork and printing hello

Question

Possible Duplicate:
Working of fork() in linux gcc
Why does this code print two times?

#include<stdio.h>
main()
{

 printf("hello\n");
 fork();

}

The above code prints "hello" one time.The code below prints "hello" two times.

#include<stdio.h>
main()
{

 printf("hello");
 fork();

}

The code above prints "hello" two times.

Please Somebody explain this strange behavior.

this has been asked multiple times before. Please use the search function.. — stefan, Oct 19 '12 at 13:29
The output buffer is copied to the child, and without newlines, it's not empty. — Daniel Fischer, Oct 19 '12 at 13:30

score 3 · Accepted Answer · answered Oct 19 '12 at 13:36

It's not guaranteed to behave in this way, but the usual behaviour is: With

printf("hello");

the "hello" is printed to the output buffer, but that buffer is not yet flushed. Then upon the

fork();

the program state is copied to the child process, including the non-empty output buffer. Upon exit, the output buffers of parent and child are both flushed.

With the newline, the output buffer is flushed before the fork().

Running fork and printing hello

1 Answers1