fork() and redirection

[Richard L Andrews]

Why does the fork command start the child process at the point where
it occurs in the program normally, yet restart the child process when
the output is redireced to a file?  (I am using the tsch shell on UNIX).

Example:
--------
Code:
-----
#include <stdio.h>

main(

     printf("This is a test.\n");
     printf("Statement 2 in main.\n");
     if (fork() == 0) {
          printf("Child statement 1\n");
          printf("Child statement 2\n");
     } else {
          printf("Parent statement 3\n");
          printf("Parent statement 4\n");
     }
}

when output to terminal:
------------------------
This is a test.
Statement 2 in main.
Parent statement 3
Parent statement 4
Child statement 1
Child statement 2

When piped to a file, the file reads:
-------------------------------------
This is a test.
Statement 2 in main.
Parent statement 3
Parent statement 4
This is a test.
Statement 2 in main.
Child statement 1
Child statement 2


When displayed on the terminal, although the output can be
undetermined, it never prints "This is a test." twice.

Much thanks in advance.
-Rich
-- 
  //   Richard L Andrews II   |"Like any good philosophical discussion, the
\X/ andrewsr at topaz.rutgers.edu| conclusion is left unresolved." -McLaughlin