Overview
This bulletin explains the layout of Clarion index and key files. Clarion Index and Key Files While Technical Bulletin #117, «Clarion Data File,» covered the layout of Clarion Professional Developer’s data files, it only touched on the subject of the index and key files that Professional Developer uses to access your data in a specific order.  The purpose of this technical bulletin is to explain how Clarion’s key and index files are laid out.
This technical bulletin assumes a knowledge of basic data structures and the C programming language.  While you don’t have to be a C guru to understand the material presented here, a passing knowledge helps, as C makes it easy to create many types of data structures.
As far as this discussion is concerned, there are NO internal differences between index and key files.  Index files are simply key files that are not updated automatically by adding, deleting, of changing records in your data base. Also, this bulletin will not explain how you create key files, only how to read them.  Our method of managing B+ Trees is proprietary and quite complicated.  In all fairness, we can only support products that create key files using our own code.  When you see a non-Clarion product that creates and/or maintains Clarion key files, it means they have licensed our code for use in their product. Читать далее →

Overview
This bulletin explains the format of Clarion data files.

Clarion Data Files
This technical bulletin explains the format of data files created by the
Clarion Professional Developer and the Clarion Personal Developer (Version 2 and
above).  It will only cover data files; key and index files are covered in
Clarion Technical Bulletin #118.  Use this information carefully because an
erroneous change to a data file will make your file unreadable.  Due to the
risks of data integrity, encryption is not covered in this bulletin.
A file defined with Clarion contains a lot of information on data such as
fields, keys, indexes, pictures, arrays, etc.  When the file is first
created, you will have a .DAT file and optionally one or more .K??, .I??, and .MEM
files (where ?? is a two digit number).  The .DAT file also contains
information on keys, fields and their layouts, and many fields that allow
Professional Developer to efficiently use the space on your disk.
First, let us discuss the .DAT file.  This file consists of several
sections (some sections are optional): Читать далее →