Any function returning a string pointer will return
NULL if an error occurs. Functions returning an integer will return one of the following:
E_OK
The function was successful.
E_SYSTEM_ERROR
There was a system error during the call.
E_BAD_ARGUMENT
One or more of the arguments passed to the function was incorrect.
E_POSTED
The form is already posted.
E_CONNECTED
A field was already connected to a form.
E_BAD_STATE
The function was called from within an initialization or termination routine.
E_NO_ROOM
The form does not fit within the subwindow.
E_NOT_POSTED
The form is not posted.
E_UNKNOWN_COMMAND
The form driver does not recognize the request passed to it.
E_NOT_SELECTABLE
The field could not be selected.
E_NOT_CONNECTED
The field is not connected to a form.
E_REQUEST_DENIED
The form driver could not process the request.
E_INVALID_FIELD
The field is invalid.
E_CURRENT
The field is the active one on the form.