#c #ffi #syntex


Write C code inline in your rust code (hacky fork of rust-cpp / cpp crate)

2 releases

Uses old Rust 2015

0.1.2 Apr 10, 2018
0.1.1 Apr 28, 2017
0.1.0 Apr 24, 2017

#1566 in Rust patterns

25 downloads per month

MPL-2.0 license

450 lines


Forked from rust-cpp version 0.1.0 for situations where a full C++ compiler isn't available or warranted. Pretty hacky implementation, intended to get a few bits and pieces bootstrapped until Rust matures enough that some C code can be replaced. I couldn't have written this myself from scratch, so hats off to @mystor. One day this crate may disappear and be subsumed into rust-cpp.

Comments that follow are from rust-cpp with minor changes of C++ and cpp to C and c, etc.

rust-c is a build tool & macro which enables you to write C code inline in your rust code.

NOTE: This crate works on stable rust, but it is not stable itself. You can use this version all you want, but don't be surprised when a 0.2 release is made which completely breaks backwords compatibility. I view this crate as more of an experiment than a product.

As the tools come into stable rust to make this more practical to use, I expect that it will stabilize. Namely, I do not expect that this module will have a stable-ish interface until we get a stable procedural macro system.


Add c as a dependency to your project. It will need to be added both as a build dependency, and as a normal dependency, with different flags. You'll also need a build.rs set up for your project.

# ...
build = "build.rs"

# ...
c = { version = "0.1.0", features = ["build"] }

# ...
c = { version = "0.1.0", features = ["macro"] }

You'll also then need to call the c build plugin from your build.rs. It should look something like this:

extern crate c;

fn main()
    c::build("src/lib.rs", "crate_name", |cfg|
        // cfg is a gcc::Config object. You can use it to add additional
        // configuration options to the invocation of the C compiler.


In your crate, include the cpp crate macros:

extern crate c;

Then, use the c! macro to define code and other logic which you want shared between rust and C. The c! macro supports the following forms:

    // Include a C header into the C shim. Only the `#include` directive 
    // is supported in this context.
    #include <stdlib.h>
    #include "foo.h"
    // Write some logic directly into the shim. Either a curly-braced block or
    // string literal are supported
        #define X 10
        struct Foo
            uint32_t x;
    raw r#"
        #define Y 20
    // Define a function which can be called from rust, but is implemented in
    // C. Its name is used as the C function name, and cannot collide with
    // other C functions. The body may be defined as a curly-braced block or 
    // string literal.
    // These functions are unsafe, and can only be called from unsafe blocks.
    fn my_function(x: i32 as "int32_t", y: u64 as "uint32_t") -> f32 as "float"
        return (float)(x + y);
    fn my_raw_function(x: i32 as "int32_t") -> u32 as "uint32_t" r#"
        return x;
    // Define a struct which is shared between C and rust. In C-land its
    // name will be in the global namespace (there's only one)! In rust it will be located 
    // wherever the c! block is located
    struct MyStruct
        x: i32 as "int32_t",
        y: *const i8 as "const char*",
    // Define an enum which is shared between C and rust. In C-land it 
    // will be defined in the global namespace as an `enum` (there's only one)!. In rust,
    // it will be located wherever the c! block is located.
    enum MyEnum
        A, // Known in C as `A`

c also provides a header which may be useful for interop code. This header includes <stdint.h>. This header, rust_types.h, can be included with:-

    #include "rust_types.h"

The full body of rust_types.h is included below.

#ifndef _RUST_TYPES_H_
#define _RUST_TYPES_H_

#include <stdint.h>

typedef int8_t i8;
typedef int16_t i16;
typedef int32_t i32;
typedef int64_t i64;
typedef intptr_t isize;

typedef uint8_t u8;
typedef uint16_t u16;
typedef uint32_t u32;
typedef uint64_t u64;
typedef uintptr_t usize;

typedef float f32;
typedef double f64;

typedef u8 bool_;

typedef uint32_t char_;


Warning about Macros

rust-cpp cannot identify and parse the information found in cpp! blocks which are generated with macros. These blocks will correctly generate rust code, but will not generate the corresponding C++ code, most likely causing your build to fail with a linker error. Do not create cpp! {} blocks with macros to avoid this.


~11K SLoC