Mega Code Archive

 

Categories / Delphi / Examples

 

Are 2 files identical do a 32bit crc sum

To determine, whether 2 files are identical, I first would compare their sizes. If they are identical, I would calculate a 32bit CRC sum for each of them and compare the results. It is extremely unlikely that the files are different but have the same CRC. Someone asked me: "Are you sure? Take for example two files, where the only difference would be that in one of them, I turned a "hello" into a "ehllo". I guess the checksum would be the same, don't you think?" Answer: No, a CRC might even tell you where the difference was (if the files are really that short). The following function does compute such a 32bit CRC (cyclic redundancy check) value: function ComputeFileCRC32(const FileName : string): LongInt; Since the polynome table is rather long, you may download the pascal file: crc32.zip (2.2kB). To compare, use something like this: function Ident (const fn1, fn2 : string) : boolean; begin Ident := ComputeFileCRC32(fn1) = ComputeFileCRC32(fn2); end;