When modifying a file, is it always necessary to rewrite the entire file?

Question

When modifying a file, is it always necessary to rewrite the entire file or is it possible to find and change some small part of a file without having to rewrite the whole thing?

Answer 1

If you're not inserting or deleting data, then you don't need to rewrite the file. You will be replacing existing bytes with new values, or appending to the file.

If you need to insert or delete, you only need to rewrite the file from that point onwards. The only time you would need to rewrite the entire file is if you are inserting bytes at the beginning.

It's okay to open a file with both read and write permissions. That way you can search the file for whatever you're looking for, and once you have the position you can seek to it (from memory, the write pointer is separate from the read pointer) and overwrite data to your heart's content =)