sed - please help me

Hi

I want extract class names from C++ file sources. So I think sed will
perfeclty fit my needs. I wrote two almos identical sed commands, but
second completly does not work. Please tell me why?

First command:
$ sed -n '/^class[[:space:]]\+[[:alpha:]]\+.*$/p' ./User.h
class RoomState
class UserBase
class UserData : public UserBase
class User : public UserBase

And similiar but with simple transformation:
$ sed -n 's/^class[[:space:]]\+\([[:alpha:]]\+\).*$/\1/' ./User.h
[no output]


thank you
Szyk