when are the xxxin() functions called

Hello,

I'm trying to figure out when the following functions are called,

charin()
int2in()
int4in()
textin()

I used GDB for debuging. I set break points at each function and I did
following testing.

create table abcin( id integer, name varchar(10), title text);
insert into abcin( id, name, title ) values (1,'tom', 'manager');

The result is, textin() was called to handle 'manager' assigned to
title, but charin(), int2in and int4in were not called.

Does anyone know when are charin(),int2in() and int4in() called?

Thanks,

Rui Hai