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Level: 101 · for anyone starting from zero

One line: C is a small language with a large amount of "it depends", and this library runs every example on two machines that disagree — so each page can say which answers are C's and which are your compiler's.

What this library is for

Being able to build, read and debug C you did not write — a repository with a Makefile at the top, the benchmarks from a conference talk, the C view on a page in a sibling library — and to know, for anything a program prints, whether you are looking at the language or at your machine.

How a lesson works

  • The page — one idea, opening with the version that works, then the trap.
  • examples/ — the programs behind the page. A block marked Verified output was pasted in by a tool from a real run, and CI runs it again on Ubuntu and on macOS on every push.
  • demo/ — files meant to be copied: a Makefile and the sources it builds. A Makefile shown on a page is the demo file byte for byte, TABs included — which matters, because make refuses a recipe line indented with spaces.
  • A fence titled Real output — … — one run on one named machine, kept because it shows a difference between machines. CI does not re-run it, and its title says where it came from.

Running an example yourself

git clone https://github.com/masiarek/c-learning-library
cd c-learning-library/01_Building/makefiles/examples
bash makefiles_rebuild_sh.sh
python3 ../../../tools/run_examples.py --only makefiles_rebuild_sh

The first command prints what the page's verified block shows. The last one checks that output against the recorded answer key and tells you if your machine disagrees — which, in a C library, is sometimes the lesson.

The chapters

Chapter What it covers
01_Building The compiler, the linker and make — what turns .c files into a program, and what decides which of them to rebuild

Planned

Rough order, not a promise:

  • Integers — widths, promotions, signed overflow, and <stdint.h>
  • Strings are arrays — the terminating NUL, strlen against sizeof, and the library functions that do not check a length
  • Pointers and memory — malloc and free, lifetimes, and what AddressSanitizer catches
  • Undefined behaviour — what the standard declines to define, and why the optimizer cares. The Rust library's C and C++ chapter ↗ already runs nine of them