|char **||GetUsedFields ()|
|char ** OGRFeatureQuery::GetUsedFields||(||)|
Returns lists of fields in expression.
All attribute fields are used in the expression of this feature query are returned as a StringList of field names. This function would primarily be used within drivers to recognise special case conditions depending only on attribute fields that can be very efficiently fetched.
NOTE: If any fields in the expression are from tables other than the primary table then NULL is returned indicating an error. In succesful use, no non-empty expression should return an empty list.