6502.org

Sometimes have a second implementation of something is handy so as there is a bit of chatter about FAT32 I'm posting a C++ implementation I've done below (that includes reading, writing, seeking, formatting):

It was initially based on (stolen from) Fernando Rodriguez's implementation and is pretty thoroughly tested. The two big changes I made were to rewrite it in C++ with a focus on shorter more readable methods and adding a cache behind the file system. I've used it for reading SD cards on a Raspberry Pi Pico but it's ultimately supposed to be the file system for a 65C816 based computer.

A good starting point is:
FatFile.h
FatFile.cpp
that includes the Open, Close, Write, Read, Seek, Flush, Truncate, Tell and Size methods.

and from there backing up to the:
FatCommon.h
file that defines all of the FAT file structures.

then if you're brave take a look in:
FatVolume.h
FatVolume.cpp
that finally do the work to deal with the awful mangled cluster system that is FAT.

a FAT Volume sits on top of an implementation of a:
FileDrive.h
FileDrive.cpp
that is some form of block device. In my case an SD card whose implementation is in another library.

Tests can be found in:
TestFat32.cpp
TestFatCache.cpp

If you want to get this compiling and running you'll need Windows with Visual Studio 2019 and then clone the two repositories: and then message me because I think there is one project level variable that needs to be setup and I cannot remember what it is off of the of my head. And I'm assuming people are only going to read this implementation for reference, not try and run it.