mohitmishra786/low-level-dev-skills

zig-cinterop

Zig C interoperability skill.

소스 보기

사용 방법

  1. 설치 명령을 복사하고 자신의 에이전트 환경에 설치하기 전에 소스 패키지를 확인하세요.
  2. 필요한 도구, 인증 정보, 지원 환경은 원본 문서에서 확인하세요.
  3. 입력과 원하는 산출물을 설명하고 출처와 결과를 대조하세요.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill zig-cinterop

시작 전 확인

  • 설치에는 모델 구독, API 한도, 파일 접근 권한이 포함되지 않습니다.
  • 별점 수와 설치 수는 활동 지표이며 독립적인 품질·보안 검증이 아닙니다.
원본 Skill 문서

원본 저장소의 제목, 예시, 코드, 표, 링크, 이미지를 유지해 표시합니다.

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 typeZig type
intc_int
unsigned intc_uint
longc_long
unsigned longc_ulong
long longc_longlong
size_tusize
ssize_tisize
char *[*:0]u8 (null-terminated)
const char *[*:0]const u8
void **anyopaque
NULLnull
boolbool (C99) or c_int (older)
floatf32
doublef64
zig
// Passing strings to C
const str = "hello";
_ = c.puts(str);  // Zig string literals are [*:0]const u8

// Dynamic strings — need null terminator
var buf: [64:0]u8 = undefined;
const len = std.fmt.bufPrint(buf[0..63], "hello {d}", .{42}) catch unreachable;
buf[len] = 0;
_ = c.puts(&buf);

4. extern struct — ABI-compatible structs

Use extern struct to match a C struct's memory layout exactly:

zig
// Matches: struct Point { int x; int y; };
const Point = extern struct {
    x: c_int,
    y: c_int,
};

// Matches: struct Header { uint32_t magic; uint16_t version; uint16_t flags; };
const Header = extern struct {
    magic: u32,
    version: u16,
    flags: u16,
};

// Use with C API
var p = Point{ .x = 10, .y = 20 };
_ = c.draw_point(&p);

5. packed struct — bit-level layout

zig
// Matches C bitfield: struct { uint8_t flags : 4; uint8_t type : 4; };
const Flags = packed struct(u8) {
    mode: u4,
    kind: u4,
};

// Packed struct for wire protocols
const IpHeader = packed struct(u32) {
    ihl: u4,
    version: u4,
    tos: u8,
    total_length: u16,
};

var h: IpHeader = @bitCast(@as(u32, raw_bytes));

6. Exporting Zig to C

zig
// Export a function callable from C
export fn zig_add(a: c_int, b: c_int) c_int {
    return a + b;
}

// Export with specific calling convention
pub fn my_func(x: u32) callconv(.C) u32 {
    return x * 2;
}

// Export a struct (use extern struct for C layout)
export const VERSION: c_int = 42;

Generate a C header (manual or with tools):

c
/* mylib.h */
#ifndef MYLIB_H
#define MYLIB_H
#include <stdint.h>

int zig_add(int a, int b);
uint32_t my_func(uint32_t x);
extern int VERSION;

#endif

7. Calling Zig from C in build.zig

zig
// Build Zig as a C-compatible static library
const lib = b.addStaticLibrary(.{
    .name = "myzig",
    .root_source_file = b.path("src/lib.zig"),
    .target = target,
    .optimize = optimize,
});

// The C code that uses the Zig library
const c_exe = b.addExecutable(.{
    .name = "c_consumer",
    .target = target,
    .optimize = optimize,
});
c_exe.addCSourceFile(.{
    .file = b.path("src/main.c"),
    .flags = &.{"-std=c11"},
});
c_exe.linkLibrary(lib);
c_exe.linkLibC();
b.installArtifact(c_exe);

8. Opaque types and forward declarations

zig
// Forward-declared C struct (opaque)
const FILE = opaque {};
extern fn fopen(path: [*:0]const u8, mode: [*:0]const u8) ?*FILE;
extern fn fclose(file: *FILE) c_int;
extern fn fprintf(file: *FILE, fmt: [*:0]const u8, ...) c_int;

// Opaque handle pattern
const MyHandle = opaque {};
extern fn lib_create() ?*MyHandle;
extern fn lib_destroy(h: *MyHandle) void;

9. Variadic functions

zig
// Call variadic C functions using @call with variadic args
const c = @cImport(@cInclude("stdio.h"));

// printf works directly through @cImport
_ = c.printf("value: %d\n", @as(c_int, 42));

// For custom variadic C functions, use extern with ...
extern fn my_log(level: c_int, fmt: [*:0]const u8, ...) void;

For translate-c output guide and C ABI types reference, see references/translate-c-guide.md.

Related skills

  • Use skills/zig/zig-compiler for zig cc C compilation and basic Zig builds
  • Use skills/zig/zig-build-system for build.zig with mixed C/Zig projects
  • Use skills/binaries/elf-inspection to verify symbol exports and ABI
  • Use skills/rust/rust-ffi for comparison with Rust's C FFI approach

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