delphi compare text file contents

Question

We need to compare the contents of two (or more) text files to determine if we need to create a backup. If they differ we create a new backup.

I currently use the CRC value of each file to check for differences but I was wondering if there is a more efficient or elegant way of detecting differences between to files.

//Use madZIP to calculate the CRC fior this file
GetUncompressedFileInfo(Filename_1, Size_1, NewCRC);

//Use madZIP to calculate the CRC fior this file
GetUncompressedFileInfo(Filename_2, Size_2, OldCRC);

//if ThisFileHash = ExistingFileHash then
if (OldCRC <> NewCRC) then
  CreateABackup;

Regards, Pieter.

Answer 1

CRC is not a safe method to detect file changes - cryptographic hashes (like MD5 or SHA1) are much better.

Another approach (like the one used by build systems) is to compare file dates. If the file is newer than backup, a new backup is needed.

Answer 2

CRC is probably more accurate, and pretty efficient. However do you need to check the contents?

I'm assuming you're checking the CRC to see if a modification has been made and re-backup the updated file. In which case FileAge() would do just fine.