---
title: bt.h
related:
  - "[cum.h](cum.h.md)"
categories:
  - C libraries
---

**bt.h** is a single-header red-black tree for C with string keys. Adding,
finding and deleting are O(log n), and deleting keeps the tree balanced.

Walks in key order (`bt_first`/`bt_next`, or `for_bt_each`) keep no state of
their own, so they can nest. The older `bt_iter` still works, but has a
single state for the whole program.

## Usage

1. Copy `bt.h` into your project.
2. `#define BT_IMPLEMENTATION` before including it, in exactly one file.
3. `#include "bt.h"` wherever you need it.

The public API is documented in `bt.h`; `test.c` is an example.

> [!NOTE]
> If you get *implicit declaration of function strdup*, include `bt.h` before
> `string.h`, or define `_XOPEN_SOURCE >= 500` or
> `_POSIX_C_SOURCE >= 200809L`.

The tree is not type-agnostic yet.

## See also

- [Source code](https://github.com/hugoocoto/bt.h)