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From: defaria@hpcupt3.cup.hp.com (Andy DeFaria)
Newsgroups: comp.lang.pascal
Subject: Reading other programs variable length records?
Message-ID: <45670016@hpcupt3.cup.hp.com>
Date: 16 May 91 17:33:53 GMT
Organization: Hewlett Packard, Cupertino
Lines: 60

I'm trying to read a file, output  by another  program, with TP that  has a
certain, predefined format and I'm having  some difficulties.  I have a few
questions about this.

First, the format of the file is roughly as:

	RecordType   : Integer
	RecordLength : Integer
	Data         : { varies }

Questions:

     1) RecordType  should really be  an enumeration but the  values of the
	enumeration are fixed and  non-sequential.  Is there  a way  that I
	can tell TP what I want the enumeration values to be?  In Ada I can
	do this.

     2) Trying  to use a variant record  in  TP doesn't work because  1) it
	would require the record to be defined as:

		RecordLength : Integer
		RecordType   : Integer
		Data	     : { varies }

	or I  could put RecordLength in  each Data field.  Still attempting
	to do:
	
		Var
		   FromFile   : File of ThisCrazyRecordType;
		   ARecordVar : ThisCrazyRecordType

		   Read (FromFile, ARecordVar);

	would cause the  largest record variant  to be read  in and this is
	not what I want since the size of the  records is not  constant but
	varies with  the  record  type.  So the question   is:  How do  you
	define this type of a record?

I can see a way to do this but it  doesn't seem ideal and I'm  wondering if
there is  a  better  way.  Basically  my work around  consists of writing a
procedure to read every  type  of record  and  assembling a  Pascal variant
record of all record types layed out any way I want:

Procedure ReadTheFunnyRecord (Var FromFile   : File;
                              Var ReturnData : ThisCrazyRecordType);

Var
   Header : HeaderType;
   Data   : DataType;

Begin
   BlockRead (FromFile, Header, SizeOf (Header));
   BlockRead (FromFile, Data, Header.Length));

   Case Header.RecordType of
      { Large case statement to change RecordType to an ascending }
      { enumeration value in ReturnData and format the Data portion of }
      { ReturnData }
   end;

end;