2018q3 Homework2 (lab0)

contributed by <KittyLiou>

After the first time I finished the implementation of queue.c and queue.h, I got 93/100.

Below is the error message:

+++ TESTING trace trace-06-string:
# Test of truncated strings
ERROR: Removed value meerkat_panda_squirrel_vultureXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX != expected value meerkat_panda_squirrel_vulture

trace-06-string.cmd

\# Test of truncated strings
option fail 0
option malloc 0
new
ih aardvark_bear_dolphin_gerbil_jaguar 5
it meerkat_panda_squirrel_vulture_wolf 5
rh aardvark_bear_dolphin_gerbil_jaguar
reverse
rh meerkat_panda_squirrel_vulture_wolf
option length 30
rh meerkat_panda_squirrel_vulture
reverse
option length 28
rh aardvark_bear_dolphin_gerbil
option length 21
rh aardvark_bear_dolphin
reverse
option length 22
rh meerkat_panda_squirrel
option length 7
rh meerkat
reverse
option length 8
rh aardvark
option length 100 
rh aardvark_bear_dolphin_gerbil_jaguar
reverse
rh meerkat_panda_squirrel_vulture_wolf
free
quit

After execute each line one by one, I found the problem was caused by the line:
rh meerkat_panda_squirrel_vulture

In qtest.c, we can see that the function of rh is to remove the head of the queue and optionally compare the returned string to the expected string.

add_cmd("rh", do_remove_head,
        " [str]          | Remove from head of queue.  Optionally compare "
        "to expected value str");

Now, I can know that the problem lies in the function bool q_remove_head(queue_t *q, char *sp, size_t bufsize) in queue.c

By the error message, the returned string seems to have something wrong. It has a lot of weird paddings. This is usually caused by the missing of \0 at the end of the sting. Without \0, the string didn't end at the proper position but kept looking for a terminator until it found one.

After I modified the code to append \0 at the end of the returned string, everything went smoothly!