I'm searching for a good way to add meta data to a file. dsofile.dll works fine for NTFS. The meta data is lost, when one drops a copy on a FAT32 share (it uses NTFS hidden streams I guess). Microsoft Word documents contain meta data that are not lost, how do they do it? Similiar to FAT, sending the file via E-Mail strips of all meta data created with dsofile (and also meta data created by hand with Windows Explorer). Separate meta data files are not an option. It must be compatible with standard Windows techniques. If I send someone a file with Outlook and he sends it back, the meta-data should not be lost.
(the required meta data is actually only an ID)
Any solution would be format-dependent. MS OFfice files are (all) compound files and there's a place for properties there. In some formats (PE files, for example) it's safe to just append data to the end of the file, if you know how to read them later. In ZIP file you can probably find a place in the directory or just add a helper file with your data to the archive. Other formats can't stand this, and you'd need to find your own way at solving the problem.
Actually, file name can also be a good placeholder for your ID.
If you need to store the files somewhere but don't need the file to remain readable by outside applications, you can pack them to ZIP archive or use something like our SolFS library.