[cs631apue] Weird Output when use pipe

[bzhang41]

Hi all,

I am a little confused why the output my program is not stable I when I 
try to use pipe.

If I test separately,
./aed -e <file >file.enc
./aed -d <file.enc

I always get the correct answer:
Hi Alice, I am Bob !
Hi bob!

However, interesting thing happened when I use pipe, each time I try, it 
will
output different result, sometimes it is correct, sometimes it is not. 
The
following is the output of the test:

bzhang41 at nemo:~/hw4$ cat file | ./aed -e | ./aed -d
?r?}??? , I am Bob !
Hi bob!
bzhang41 at nemo:~/hw4$ cat file | ./aed -e | ./aed -d
`???*, I am Bob !
Hi bob!
bzhang41 at nemo:~/hw4$ cat file | ./aed -e | ./aed -d
????T??, I am Bob !
Hi bob!
bzhang41 at nemo:~/hw4$ cat file | ./aed -e | ./aed -d
Hi Alice, I am Bob !
Hi bob!
bzhang41 at nemo:~/hw4$ cat file | ./aed -e | ./aed -d
Hi Alice, I am Bob !
Hi bob!
bzhang41 at nemo:~/hw4$ cat file | ./aed -e | ./aed -d
S?pYY?e, I am Bob !
Hi bob!
bzhang41 at nemo:~/hw4$ cat file | ./aed -e | ./aed -d
?8?R?J, I am Bob !
Hi bob!
bzhang41 at nemo:~/hw4$ cat file | ./aed -e | ./aed -d
Hi Alice, I am Bob !
Hi bob!