Windows® via C/C++, Fifth Edition

Working with File Devices

Because working with files is so common, I want to spend some time addressing issues that apply specifically to file devices. This section shows how to position a file’s pointer and change a file’s size.

The first issue you must be aware of is that Windows was designed to work with extremely large files. Instead of representing a file’s size using 32-bit values, the original Microsoft designers chose to use 64-bit values. This means that theoretically a file can reach a size of 16 EB (exabytes).

Dealing with 64-bit values in a 32-bit operating system makes working with files a little unpleasant because a lot of Windows functions require you to pass a 64-bit value as two separate 32-bit values. But as you’ll see, working ...