Project 8: File I/O System

A comprehensive file I/O library handling text and binary files, buffering strategies, serialization with endianness handling, and cross-platform compatibility.

Quick Reference

Attribute Value
Primary Language C
Alternative Languages None
Difficulty Level 3 - Advanced
Time Estimate See main guide
Knowledge Area I/O, Operating Systems
Tooling GCC, strace/dtrace
Prerequisites See main guide

What You Will Build

A comprehensive file I/O library handling text and binary files, buffering strategies, serialization with endianness handling, and cross-platform compatibility.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Buffering modes → Maps to understanding stdio internals
  • Binary I/O with endianness → Maps to portable data formats
  • Error handling in I/O → Maps to robust file operations

Key Concepts

  • Map the project to core concepts before you code.

Real-World Outcome

# 1. Buffering mode demonstration
$ ./file_io buffering
=== Line Buffered (stdout default) ===
Writing without newline... [1 second pause]
Now with newline:
Output appears immediately!

=== Fully Buffered (file default) ===
Writing to file... [writes to buffer]
Buffer size: 8192 bytes
Writing 100 bytes... (not yet on disk)
After fflush: now on disk
After fclose: definitely on disk

=== Unbuffered (stderr default) ===
Each write goes directly to OS (slow but immediate)

# 2. Binary file format with endianness
$ ./file_io binary_write test.bin
Writing struct to file in portable format...
Platform is: little-endian
File format: big-endian (network byte order)
Converting before write:
  int32 12345678 -> bytes: 0x00 0xBC 0x61 0x4E
  float 3.14159 -> bytes: 0x40 0x49 0x0F 0xD0
Wrote 16 bytes to test.bin

$ ./file_io binary_read test.bin
Reading portable format...
Converting from big-endian to native...
Recovered values:
  int32: 12345678
  float: 3.14159
Cross-platform compatible!

# 3. System call tracing
$ strace -e read,write ./file_io syscalls
read(3, "Hello, World!\n", 4096) = 14  # One read for small file
write(1, "File contents: Hello, World!\n", 30) = 30
...
Buffered reads reduce syscall count by 10-100x!

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: PROFESSIONAL_C_PROGRAMMING_MASTERY.md
  • Effective C, 2nd Edition by Robert C. Seacord