Solved

Record alignment, Delphi 4 vs Delphi 5

Posted on 2000-02-14
6
592 Views
Last Modified: 2010-04-04
I wrote to a file in Delphi 4 using the following record structure:

TRouteFileHeader = record      // 40 in Delphi 5, 32 in Delphi 4
  HRouteId: string[8];              // 9
  HRouteVersion: string[5];     // 6
  HOperationCount: Integer;  // 4
  HLoadDate: TDateTime;       // 8
  HFileVersion: string[2];        // 3
end;

I recompiled in Delphi 5 and tried to read the same file. The first three fields were okay, but the last two were not. When I did a sizeof on the record, it was 40 bytes. In Delphi 4 it was only 32 bytes (which seems about right).

I think this may have something to do with aligning records on 32 bit boundries. I tried to change that setting, and it did make a difference. I couldn't get the Delphi 5 program to correctly read the file though.

My question is, is there a setting in Delphi 5 that will allow it to correctly read this file as written in Delphi 4?
0
Comment
Question by:wipnav
  • 3
  • 3
6 Comments
 
LVL 12

Accepted Solution

by:
rwilson032697 earned 200 total points
ID: 2520868
The answer is no, there is not setting (sorry). You need to declare your record like this if the D4 record size was 32:

TRouteFileHeader = packed record
  HRouteId: string[8];            
  Dummy1 : Byte;
  HRouteVersion: string[5];    
  Dummy2 : Byte;
  HOperationCount: Integer;  
  HLoadDate: TDateTime;      
  HFileVersion: string[2];      
end;

In general, any record that you write to a file should be declared as 'packed'

Cheers,

Raymond.
0
 
LVL 1

Author Comment

by:wipnav
ID: 2520922
Thanks for your help. I will try that.
0
 
LVL 12

Expert Comment

by:rwilson032697
ID: 2520933
Your welcome.

As a general rule experts here do not mind if you verify an answer works for you before grading.

Let me know how it goes.

Cheers,

Raymond.
0
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 1

Author Comment

by:wipnav
ID: 2525231
Raymond,

I tried it today and didn't work. I think using a packed record made things worse. I didn't get a chance to document exactly what I got, but it didn't look too good. I still wonder what they changed in Delphi 5 to cause this problem.

Regards,

Bill
0
 
LVL 12

Expert Comment

by:rwilson032697
ID: 2525316
I found the definitive guide in section 18-7 of the D3 Object Pascal Guide. According to that, the record should look like this (sorry for the incorrect initial answer):

TRouteFileHeader = packed record
  HRouteId: string[8];            
  HRouteVersion: string[5];  
  Dummy1 : Byte;    
  HOperationCount: Integer;  
  HLoadDate: TDateTime;        
  HFileVersion: string[2];        
  Dummy2 : Byte;
end;

I don't think there were changes between D3 and D4, though there have been for D4 to D5.

Cheers,

Raymond.
0
 
LVL 1

Author Comment

by:wipnav
ID: 2529459
Raymond,

The second answer worked. Thanks for your help. My initial grade stands.

Regards,

Bill
0

Featured Post

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
how to center only a line in richedit? 4 69
Delphi IDE crash without error message ... 7 120
How to renew a Delphi rad-studio licence? 5 77
control image tags in a string ? 12 153
Have you ever had your Delphi form/application just hanging while waiting for data to load? This is the article to read if you want to learn some things about adding threads for data loading in the background. First, I'll setup a general applica…
Introduction I have seen many questions in this Delphi topic area where queries in threads are needed or suggested. I know bumped into a similar need. This article will address some of the concepts when dealing with a multithreaded delphi database…
A short tutorial showing how to set up an email signature in Outlook on the Web (previously known as OWA). For free email signatures designs, visit https://www.mail-signatures.com/articles/signature-templates/?sts=6651 If you want to manage em…
Attackers love to prey on accounts that have privileges. Reducing privileged accounts and protecting privileged accounts therefore is paramount. Users, groups, and service accounts need to be protected to help protect the entire Active Directory …

733 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question