c_import

This is a small proc macro crate providing a c_import macro (also a cpp_import macro), which can be used to import C headers into your program. It leverages bindgen, so bindgen needs to be installed in your system. It also works in no_std mode.

Usage

In your Cargo.toml:

# Cargo.toml

[depenedencies]
c_import = "0.2"

In your Rust source file:

// src/main.rs
use c_import::c_import;

c_import!(
    "<stdio.h>", 
    "<cairo/cairo.h>",
    "--link cairo"
);

fn main() {
    let version = unsafe { cairo_version() };
    println!("{}", version);
}

If you don't use the --link directive, you can use a Rust build script:

// build.rs
fn main() {
    println!("cargo:rustc-link-lib=cairo");
}

Using non-system headers is also possible via enclosing the header path with quotation marks:

// src/main.rs
use c_import::c_import;
c_import!("src/my_header.h");

fn main() {
    let version = unsafe { cairo_version() };
    println!("{}", version);
}

Extra clang arguments

You can pass extra clang arguments as extra arguments to the macro:

// src/main.rs
use c_import::c_import;
c_import!(
    "src/my_header.h", 
    "-DMY_DEFINE", 
    "-I/somepath/include"
);

fn main() {
    let version = unsafe { cairo_version() };
    println!("{}", version);
}

Similarly you can invoke tools like pkg-config to retrieve cflags and pass them to bindgen:

use c_import::c_import;

c_import!(
    "<cairo.h>", 
    "<stdio.h>",
    "$pkg-config --cflags cairo"
);

fn main() {
    let version = unsafe { cairo_version() };
    println!("{}", version);
}

Macro parameters

• Normal arguments are considered header files.
• Arguments starting with --link are used to insert #[link (name = libname)] attributes to the generated extern functions, this allows linking the libraries without having to explicitly create a build.rs file containing println!("cargo:rustc-link-lib=libname");
• Arguments starting with -- are considered bindgen arguments.
• Arguments starting with - are considered cflags, such as include paths or defines ("-I" & "-D" respectively).
• Arguments starting with $ are considered shell commands which return cflags, similar to pkg-config.

Usage with C++ headers (limited)

// src/main.rs
use c_import::cpp_import;

cpp_import!("<FL/Fl.H>");

fn main() {
    let version = unsafe { Fl::api_version() }; // static method of class Fl
    println!("{}", version);
}

// build.rs
fn main() {
    println!("cargo:rustc-link-lib=fltk");
}

Another example showing how to deal with C++ namespaces:

// src/my_header.hpp
#pragma once

namespace my_namespace {
class MyStruct {
    int version_;
  public:
    MyStruct(int version);
    int version() const;
};
}

// src/main.rs
use c_import::cpp_import;

cpp_import!("src/my_header.hpp");

fn main() {
    let h = unsafe { my_namespace_MyStruct::new(2) };
    println!("{}", unsafe { h.version() });
}

Limitations

• Mostly bindgen limitations:
  • with C++ headers.
  • with static inline functions.