# Patterns/callback Context

> Callback + Context Pattern (C-Specific) pattern for C development

- Skill: `majiayu000/patterns-callback-context` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds add majiayu000/patterns-callback-context`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/patterns-callback-context/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/patterns-callback-context

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# Callback + Context Pattern (C-Specific)

Pair function pointer with `void *` user data. Callback receives user data, enabling state access without globals. Universal C pattern for async/event handling.

## ikigai Application

**Streaming responses:**
```c
typedef void (*chunk_cb_t)(void *user_ctx, const char *data, size_t len);

res_t ik_llm_stream(ik_llm_client_t *client,
                    ik_message_t **msgs,
                    chunk_cb_t on_chunk,
                    void *user_ctx);  // Passed to callback
```

**Usage:** REPL passes itself as context, callback updates scrollback.

**Convention:** Callback function pointer immediately followed by `void *` context parameter. Callback signature includes context as first param.

**Benefit:** Stateful callbacks without globals. Each caller provides own context.