File I/O and Standard Library

The part of C that talks to the outside world instead of just moving values around in memory: opening files, reading and writing them, checking whether any of that actually worked, and the corners of <stdlib.h> worth actually knowing instead of looking up every time.

The four chapters

• A — File I/O Basics. fopen/fclose and the file-mode strings that decide read, write, append, binary, or some combination.
• B — Reading and Writing. fread/fwrite/fprintf/fscanf, and the buffering happening underneath that decides when data actually hits disk.
• C — Error Handling. errno, perror, and building the habit of checking return values that are extremely easy to just skip.
• D — Standard Library Essentials. The parts of <stdlib.h> that come up constantly — conversion functions, qsort, exit codes.

Where this lands in driver work

Userspace drivers talk to /dev and /sys nodes with exactly this file API — open/read/write on a device node is the same shape as fopen/fread/fwrite on a regular file, just at the syscall layer instead of buffered stdio. The error-checking discipline from Chapter C is non-negotiable there — a failed open() on a device node means something real went wrong with the hardware or permissions, not just a missing file.