'===========================================================================
' Subject: ABC FILE STRUCTURES               Date: 02-25-96 (10:42)       
' Author:  The ABC Programmer                Code: QB, QBasic, PDS        
' Origin:  The ABC Reader v1.00            Packet: ABC.ABC
'===========================================================================
' Here is the release of the ABC Packet structures

TYPE ABCFileStructure         ' Structures for *.ABC
  From AS STRING * 31         ' Programmer/Author's name
  Subject AS STRING * 31      ' Subject/Title of code
  Origin AS STRING * 31       ' Origin of code, or keywords
  DateOf AS STRING * 23       ' Date of code release
  CodeOf AS STRING * 23       ' Code of (QB,QBasic,PDS,ASIC,PB,VB,ASM,TEXT)
  NumLines AS STRING * 5      ' Number of lines in code
  NumBytes AS STRING * 9      ' Number of bytes when extracted
  SaveFile AS STRING * 12     ' Default extraction name
END TYPE

' NOTE:  (Number of bytes) - (Number of lines in code) = (Bytes in Packet)
'
'   Lines are deliminated by CHR$(227) therefore reducing [CR,LF] to just one
'   byte.  Note that the stucture is NOT similar to the .QWK packets.
'   Please do not use their structure or method of reading the ABC packets.
'
'   For best results, read blocks in 250 bytes.  4096 bytes would be best
'   if you decide to transfer them directly into the memory buffer.
'
' NOTE:  DO NOT read them into a string array, unless you know how to
'   free up LOTS of memory (XMS/EMS) just use file pointers (LONG).

DIM ABCIndex AS STRING * 78

' For the .IDX files, here's the structure:
'
' First character is NULL or a "û" for NEW or a "¯" for SPECIAL (Your code)
'
' Next 10 bytes are the position for the code in the .ABC counterpart.
' Next  5 bytes are the number of lines in the file
' Next 31 bytes are the Subject/Title of the code
' Last 31 bytes are the Author/Programmer's Name
'
' TYPE ABCIndexStructure
'   Code AS STRING * 1
'   Position AS STRING * 10
'   NumLines AS STRING * 5
'   Subject AS STRING * 31
'   From AS STRING * 31
' END TYPE

' Here's a short demostration on reading the INDEX and ABC Packet
' Make sure the following packets are in your current directory
' or change the path to compensate.

CLS

ABCFile$ = "GRAPHICS.ABC"      ' Choose an appropriate packet
IndexFile$ = "GRAPHICS.IDX"    ' and make sure they exist.

OPEN IndexFile$ FOR BINARY AS #1    ' Open the .IDX file
  GET #1, , ABCIndex      ' Get first record (Nah, too easy, always 1)
  PRINT ABCIndex          ' Display
  GET #1, , ABCIndex      ' Second record    (Nah, let's go deeper)
  PRINT ABCIndex          ' Display
  GET #1, , ABCIndex      ' Third record (OK, we'll use this for our DEMO)
  PRINT ABCIndex          ' Display
CLOSE #1

Position& = VAL(MID$(ABCIndex, 2, 10))     ' Get our .ABC byte position
                             ' ^Since the first byte is the Code chr
                             '  We must skip to the second byte and read
                             '  10 characters from the string ABCIndex

ABCHeader$ = SPACE$(165)     ' Total number of bytes in header is 165
                             ' Don't normally use this, only for DEMO
                             ' purposes.

OPEN ABCFile$ FOR BINARY AS #1      ' Open the .ABC file
  GET #1, Position&, ABCHeader$     ' Goto Position& and read contents
  PRINT ABCHeader$                  ' Display it, yes, it works!
CLOSE #1

' I'll leave the hard part (parsing the lines of code) up to you :)
'
' Remember:   TotalBytes& = VAL(NumBytes) - VAL(NumLines)
'
' Parse in 250 byte blocks ... until you over shoot TotalBytes&
' Use INSTR to find CHR$(227) and store pointers in LONG INTEGER arrays
'
' Piece of cake!  Good luck and happy programming!