### Core “make C nicer” utilities

1. **`xmalloc/xcalloc/xrealloc/xstrdup` (header: `xalloc.h`)**

   * Teaches: error handling patterns, `errno`, consistent OOM behavior.

2. **Arena allocator (header: `arena.h`)**

   * `arena_init`, `arena_alloc`, `arena_reset`, `arena_free`
   * Teaches: alignment, bump allocators, lifetime-based allocation.

3. **Dynamic buffer / string builder (header: `buf.h`)**

   * `buf_reserve`, `buf_append`, `buf_appendf`
   * Teaches: amortized growth, `vsnprintf`, safe formatting.

4. **Slice + spans (header: `span.h`)**

   * `typedef struct { uint8_t* p; size_t n; } span_u8;` etc.
   * Teaches: safer APIs than raw pointers, length-carrying.

5. **Hash map (header: `hashmap.h`)** (string→void* or string→u64)

   * Teaches: hashing, open addressing, tombstones, resizing.

6. **Bitset (header: `bitset.h`)**

   * `bitset_set/clear/test`, `bitset_find_first_zero`
   * Teaches: word operations, popcount/ctz if you want.

### C11 correctness features

7. **Compile-time assertions & type checks (header: `ctassert.h`)**

   * Wrap `_Static_assert`, plus some `_Generic` helpers.
   * Teaches: compile-time constraints, “making invalid states unrepresentable”.

8. **`_Generic` logging macros (header: `log.h`)**

   * `LOG_INFO("x=%d", x)` with file/line, optional type-based formatting helpers.
   * Teaches: variadic macros, `_Generic`, ergonomics.

9. **Defer/cleanup pattern (header: `defer.h`)**

   * Macro that runs cleanup at scope end (via `goto` pattern).
   * Teaches: structured cleanup in C, error paths.

10. **Optional result type (header: `result.h`)**

* `typedef struct { int ok; int err; T value; } result_T;` pattern.
* Teaches: explicit error handling, no hidden global state.

### Concurrency & atomics (C11’s “real” new power)

11. **Atomic reference counting (header: `refcnt.h`)**

* `ref_inc/ref_dec` with destructor callback.
* Teaches: `stdatomic.h`, memory ordering (start with seq_cst, then learn relax/acq_rel).

12. **Lock-free SPSC ring buffer (header: `ring_spsc.h`)**

* Single-producer/single-consumer queue.
* Teaches: atomics, cache friendliness, correctness reasoning.

13. **Thread pool (header: `threadpool.h`)** using `threads.h`

* `tp_init`, `tp_submit`, `tp_join`, `tp_destroy`
* Teaches: `thrd_t`, `mtx_t`, `cnd_t`, work queues.

14. **Once-init & singletons (header: `once.h`)**

* Use `once_flag` / `call_once` (or implement if platform lacks).
* Teaches: init races, safe global setup.

### Parsing / CLI tools (you’ll actually use these)

15. **Argument parser (header: `argparse.h`)**

* `--long`, `-s`, combined short flags, `--key=value`
* Teaches: string parsing, API design, test cases.

16. **INI parser (header: `ini.h`)**

* Minimal: sections, key=value, comments.
* Teaches: parsing state machines, callbacks.

17. **CSV reader/writer (header: `csv.h`)**

* Correct quoting/escaping.
* Teaches: edge cases, streaming parsing.

18. **Path utilities (header: `path.h`)**

* `path_join`, `path_dirname`, `path_basename`, normalize `..` and `.`
* Teaches: portability pitfalls, careful string ops.

### Systems-ish building blocks

19. **File mapping / buffered reader (header: `io.h`)**

* Portable-ish wrapper for “read whole file”, “iter lines”, “atomic write via temp+rename”.
* Teaches: robust file I/O patterns, error handling.

20. **Timing + profiling helpers (header: `timeutil.h`)**

* `now_ns()`, `stopwatch`, `scope_timer` macro
* Teaches: `timespec_get`, measurement pitfalls, microbenchmark hygiene.

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## A suggested “crash course” order (so it builds)

1–3 (xalloc/arena/buf) → 7–10 (static assert, generic, cleanup, results) → 15 (argparse) → 19 (io) → 16–18 (parsers) → 11–14 (atomics/threads) → 5–6 (hashmap/bitset) → 20 (timing) → 12/13 (ring + threadpool, as capstone)

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## Two capstone tool ideas that use a lot of the above

* **`logscan`**: fast log parser + filter + histogram (buf + argparse + csv + hashmap + timeutil)
* **`dedupe`**: file deduplicator by hashing chunks (io + hashmap + arena + threadpool)

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