Extracting and Sorting Records

For C programs LIBMAKE can generate declarations for "extract" files, which can be used to present views of the database. An example of using these functions is given in the extract_open() documentation. One of the chief reasons for using the extract file routines is that they can use a sophisticated sort facility that is capable of sorting millions of records using highly effcient algorithms.

To declare records for an extract file, use the #extract directive:

where fieldname_x is the name of a database field, for example region_code or name.

You can also specify a fieldname that does not appeaer on the database. In this case you need to specify the datatype of the field as well, using a datatype letter (as used in MAKEDB), the number of occurrences (which defaults to 1), and, for character fields, the length. For example local_address:C:4:30 would result in the extract record containing a field char local_address[4][30], and local_number:I would declare short local_number.

To define the sort order for the extract file, use the #sorton directive:

where each fieldname_x is one of the fieldnames given in the #extract directive.