don't we need to release memory before exit(1)?

Dear there,

I learned to release everything malloced before exit. however this code from die.net doesn't do it.
tsearch(3): manage binary tree - Linux man page

is it wrong or I missed something?

Since the OS in question will reclaim the memory anyway, it is not necessary. On the other hand, getting into the habit of not releasing memory when you are done with it can be a Bad Thing.