examples of non-printable characters.

[vani747]

i am using this following function in my code.
select regexp_replace( col name,'[[:cntrl:]]','u')
In this above function [[:cntrl:]] means non printable charcters..how can i give value to this function..pleas e help me.

[rski]

select regexp_replace(column_name,'[[:cntrl:]]','u')
from table_name;