As far as I know, you won't even need to "know" that ext4 is the underlying filing system...
I. e. if your binary runs in a kernel that has ext4 support, and that kernel is running in a system that has drives formatted as ext4, the kernel will read and write, as ext4, whatever your binary tells it to read and write. That's the point of the operating system - it does the nitty gritty of managing diskspace for you (among many, many other things - memory, interrupts, basic I/O, etc.).
So unless you want to do something very weird or very specialised, or you will be working with file sizes or directory structures in the terabyte size range, you can just write your app and forget about what exact underlying filing system it is going to have to work with - since the Linux kernel does that for you already...?