when privacy options enabled in profile field  . say for example - Full name field

if user select option to show full name to friends only.

then the complete field not visible in profile info to public.

how public know that there is one field namely full name that was kept in private by user

Field should be visible to everyone. privacy settings should apply to field data But not Field

actually in my opinion it should be like this

field should be visible and name should not be visible. 

Full name  : Request access to View / visible to friends only or ( on mouse over)  click to  Add friend to view details ( if user clicks on add friend then its should go to register if he is not registered . if he is registered then friend request  / requesting access by user will be sent)  If user adds him s frind then automatically he /she will gain access to all fields