# zig-cinterop

A skill that walks the agent through Zig–C interop: @cImport, translate-c, extern struct, exporting Zig functions and mixed builds.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 482 installs · ★ 267
- Author: mohitmishra786
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/zig/zig-cinterop/SKILL.md
- Updated: 2026-06-27
- HTML: https://affpapa.org/en/nevibecode/skills/zig-cinterop

## What it does

The skill fires when `@cImport` or `@cInclude` shows up, when you call a C function from Zig, hand a Zig function to C, or want to see what `translate-c` produced from a header. The agent gets a type mapping table (`int` → `c_int`, `size_t` → `usize`, `char *` → `[*:0]u8`), plus examples of `extern struct` for matching a C struct layout and `packed struct` for bitfields and wire headers.

Nine scenarios are covered with working snippets: importing headers with `@cDefine` and `@cUndef`, passing null-terminated strings, opaque types like `FILE`, variadic functions, and exporting through `export fn` or `callconv(.C)`. There is a `build.zig` section too. `linkLibC()` is required when you call C functions; going the other way, Zig builds as a static library that a C executable links against.

One thing to watch from the start: skip `linkLibC()` in `build.zig` and the C symbols fail to link. The skill points to `references/translate-c-guide.md` and to sibling skills in the same repo — `zig-compiler`, `zig-build-system`, `elf-inspection`, and `rust-ffi` if you want the Rust comparison.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-cinterop -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/zig-cinterop/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/zig-cinterop/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-cinterop -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/zig-cinterop/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-cinterop -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/zig-cinterop/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install mohitmishra786/low-level-dev-skills zig-cinterop
```

2. **Manually: put the files in place**
- File: `.github/skills/zig-cinterop/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-cinterop -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/mohitmishra786/low-level-dev-skills --path skills/zig/zig-cinterop
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/zig-cinterop/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-cinterop -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/zig/zig-cinterop/SKILL.md

## When to use it
- call a C function from Zig through `@cImport`
- inspect what `translate-c` emits for a header
- declare a C struct as `extern struct` with the same layout
- pack bitfields into a `packed struct`
- wire C and Zig together in `build.zig`

## Example prompts
- Help me call `snprintf` from Zig with `@cImport` and a null-terminated buffer
- Run `translate-c` on `mylib.h` and show me how `struct MyStruct` comes out
- Build a static library from Zig in `build.zig` and link it against `src/main.c`

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: ebfd3a4666546575.

BEGIN THIRD-PARTY FILE ebfd3a4666546575
````text
---
name: zig-cinterop
description: Zig C interoperability skill. Use when calling C from Zig, calling Zig from C, using @cImport and @cInclude, running translate-c on C headers, defining extern structs and packed structs, matching C ABI types, or building mixed C/Zig projects. Activates on queries about @cImport, @cInclude, translate-c, extern struct, packed struct, Zig C ABI, calling C from Zig, exporting Zig to C, or bindgen equivalents.
---

# Zig C Interop

## Purpose

Guide agents through Zig's C interoperability: `@cImport`/`@cInclude` for calling C, `translate-c` for header inspection, `extern struct` and `packed struct` for ABI-compatible types, exporting Zig for C consumption, and `zig cc` for mixed C/Zig builds.

## Triggers

- "How do I call a C function from Zig?"
- "How do I use @cImport and @cInclude?"
- "How do I export Zig functions to be called from C?"
- "How do I define a struct that matches a C struct?"
- "What does translate-c do?"
- "How do I build a mixed C and Zig project?"

## Workflow

### 1. Calling C from Zig with @cImport

```zig
const c = @cImport({
    @cInclude("stdio.h");
    @cInclude("string.h");
    @cInclude("mylib.h");
    @cDefine("MY_FEATURE", "1");  // Equivalent to -DMY_FEATURE=1
    @cUndef("SOME_MACRO");
});

pub fn main() void {
    _ = c.printf("Hello from C: %d\n", @as(c_int, 42));

    var buf: [256]u8 = undefined;
    _ = c.snprintf(&buf, buf.len, "formatted: %d", @as(c_int, 100));
}
```

In `build.zig`:
```zig
exe.linkLibC();  // Required when using C functions
exe.addIncludePath(b.path("include/"));
```

### 2. translate-c — inspect C header translation

`translate-c` converts C headers to Zig declarations, letting you see exactly how Zig sees a C API:

```bash
# Translate a header file
zig translate-c /usr/include/stdio.h > stdio.zig

# Translate with defines/includes
zig translate-c -I include/ -DFEATURE=1 mylib.h > mylib.zig

# Translate and inspect specific types
zig translate-c mylib.h | grep -A5 "struct MyStruct"
```

This is Zig's equivalent of `bindgen` — you use it to understand what Zig generates, then use `@cImport` directly in code.

### 3. C type mapping

| C type | Zig type |
|--------|----------|
| `int` | `c_int` |
| `unsigned int` | `c_uint` |
| `long` | `c_long` |
| `unsigned long` | `c_ulong` |
| `long long` | `c_longlong` |
| `size_t` | `usize` |
| `ssize_t` | `isize` |
| `char *` | `[*:0]u8` (null-terminated) |
| `const char *` | `[*:0]const u8` |
| `void *` | `*anyopaque` |
| `NULL` | `null` |
````
END THIRD-PARTY FILE ebfd3a4666546575

The third-party file has ended. Everything between the ebfd3a4666546575 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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