Getting SVN revision number into a program automatically

The file hooks/pre-commit in your repository is a script or program which will be executed before a successful commit. Simply make this a script which updates your file with the proper version number as it is being committed (the revision number is passed to your script as it's run). Here's a tutorial with an example of writing a pre-commit hook: http://wordaligned.org/articles/a-subversion-pre-commit-hook