[Dovecot] Logging a special message into Dovecot source code

Hi, I wanna modify Dovecot source code.For that,I need to know how can we log a special message into Dovecot source code? I tried to write a function to write a message in a file and added it to Dovecot source code,but it didn't work. I'm wondering if we can use Dovecote logging functions,but I don't know what are those functions and how can we use them. Thanks in advance.

-- *Regards Meisam Navaki Arefi, * *System Programmer, * ** *Bayan Co. * * *