Project 9: Preprocessor Metaprogramming

A comprehensive preprocessor toolkit including type-generic macros, X-macros for code generation, debugging macros, and conditional compilation patterns.

Quick Reference

Attribute Value
Primary Language C
Alternative Languages None
Difficulty Level 4 - Expert
Time Estimate See main guide
Knowledge Area Metaprogramming, Code Generation
Tooling GCC, Clang, cpp
Prerequisites See main guide

What You Will Build

A comprehensive preprocessor toolkit including type-generic macros, X-macros for code generation, debugging macros, and conditional compilation patterns.

Why It Matters

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

Core Challenges

  • Macro hygiene → Maps to avoiding macro pitfalls
  • Type-generic selection → Maps to _Generic and polymorphism
  • Code generation with X-macros → Maps to DRY principles

Key Concepts

  • Map the project to core concepts before you code.

Real-World Outcome

# 1. Debug macro demonstration
$ ./preprocessor debug
[DEBUG] main.c:42 in test_debug(): Entering function
[DEBUG] main.c:43 in test_debug(): x = 42, y = 3.14
[ERROR] main.c:45 in test_debug(): Something went wrong!
Compiled without DEBUG: (no output - macros expand to nothing)

# 2. Type-generic print
$ ./preprocessor generic
generic_print(42):       42 (as int)
generic_print(3.14):     3.140000 (as double)
generic_print("hello"):  hello (as string)
generic_print('c'):      c (as char)

# 3. X-macro enum generation
$ ./preprocessor xmacro
Enum values generated:
  STATUS_OK = 0
  STATUS_ERROR = 1
  STATUS_PENDING = 2
  STATUS_COMPLETE = 3

String conversion:
  status_to_string(STATUS_OK) = "STATUS_OK"
  status_to_string(STATUS_ERROR) = "STATUS_ERROR"

# 4. Preprocessor output inspection
$ gcc -E macros.c | head -50
# Shows expanded macros - what compiler actually sees

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