Inside Macintosh: Files
The function FSpExchangeFiles allows you to exchange the data in two files.
You can use the FSpExchangeFiles function to exchange the data stored in two files on the same volume.
FUNCTION FSpExchangeFiles (source: FSSpec; dest: FSSpec): OSErr;
The FSpExchangeFiles function swaps the data in two files by changing the information in the volume's catalog and, if the files are open, in the file control blocks. You should use FSpExchangeFiles when updating an existing file, so that the file ID remains valid in case the file is being tracked through its file ID. The FSpExchangeFiles function changes the fields in the catalog entries that record the location of the data and the modification dates. It swaps both the data forks and the resource forks.
The FSpExchangeFiles function works on both open and closed files. If either file is open, FSpExchangeFiles updates any file control blocks associated with the file. Exchanging the contents of two files requires essentially the same access permissions as opening both files for writing.
The files whose data is to be exchanged must both reside on the same volume. If they do not, FSpExchangeFiles returns the result code diffVolErr .