I fixed the problem you pointed out, and tried gdb again. this time I set break point at parse and using curl to request hello.html. I followed the instruction here cs50.stackexchange.com/questions/16688/debugging-webserver-i‌​n-c/… However, the gdb does not show any error, the code gets HTTP/1.1 200 OK. and then goes back to if(connected()), and stuck in there again..... I need some more clue.... thanks!

A minor question: I test my code with a small dictionary, which contains only 1 word "a". Valgrind reports there are 4 allocs. I drew the trie structure, it only takes 2 nodes, one is root the other is the node with is_word returning true. Why the code malloc 4?

My code passes the "check50", but I really want to fix all the error reported by valgrind. I do not understand why there is invalid read at " if (destroyer->children[j] != NULL) " by unload....

I used 1 word dictionary, valgrind reports 4 alloc and 3 free. ( I can't see why it takes 4 alloc to build a only 1 word dictionary.) And after I modified the codes, gdb does not reports any fault, the main funtion exits successfully, returning 0 and shows the "time report". Just the valgrind reports the first invalid read of size 8 at " if (destroyer->children[j] != NULL) " by unload. I edited the code and hope some hints so that I can make the code better :)

I fixed the seg fault. It's not the recursion. It's how I set the pointer destroyer. Anyway, although I got rid of the seg fault, I still have the problem: Valgrind reports total heap usage: 14 allocs, 3 frees, 3,824 bytes allocated after running with a small dictionary with only 5 words. Could you give me some hint on what's wrong with my unload function? I really want to figure out how to successfully unload all the nodes. Thanks

I added return true after free(destroyer), but still, seg fault...