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An example combining C++ and Rust libraries using the Rust cxx crate

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Rust CXX demo with CBindgen, and CMake on Windows and Linux

This is an example project to experment and show how to use Rust and C++ together in a single shared library, using C++ strengths and Rust for it's strengths too.

  • C++ can call Rust functions, with native data types (such as std::unique_ptr).
  • Rust can call C++ functions, with native data types (such as std::Box)
  • C++ can call C-compatible Rust functions.

Compile and Test (GNU Linux)

The build environment assumes to be running on Linux with GCC 6.3.1.

$ cd /path/to/project/root/

$ bash build_linux.bash

# Run tests
$ ./install/bin/mmscenegraph_tests
2 + 2 = 4
SCENEGRAPH: Add SceneGraph 42
SCENEGRAPH: Remove SceneGraph 0x96b5b0
my awesome demo
done with ThingC

Note: If you are using CentOS 7.8 and require the Red Hat Developer Toolset 6 (GCC 6.3.1) for compatiblity with the VFX Reference Platform CY2018, then you can use the following commands prior to running build_linux.bash:

$ export CC=/opt/rh/devtoolset-6/root/usr/bin/gcc
$ export CXX=/opt/rh/devtoolset-6/root/usr/bin/g++
$ export _GLIBCXX_USE_CXX11_ABI=0  # Use the old std::string and std::list ABI.

# Enable Red Hat Developer Toolset 6
$ scl enable devtoolset-6 bash

Compile and Test (Microsoft Windows)

This has been tested on Windows 10, with Visual Studio 2015.

Make sure the following commands are run in the Visual Studio 2015 enabled Command Prompt.

> cd C:\path\to\project\root\

> build_windows64.bat

> install\bin\mmscenegraph_tests.exe
2 + 2 = 4
SCENEGRAPH: Add SceneGraph 42
SCENEGRAPH: Remove SceneGraph 0x1ffc8819410
my awesome demo
done with ThingC

Dependencies

You will need the Rust compiler and a C/C++ compiler. Below are the tested dependancy versions, for both Linux and Windows (MacOSX has not been tested).

This demo targets the C++11 standard.

  • Linux
    • GCC 6.3.1
  • Windows 10
    • MSVC - Visual Studio 2015
  • Linux or Windows
    • CMake 2.8.12+
    • Rust 1.48
      • cbindgen
      • cxx 1.0.26
      • libc
    • cxxbridge-cmd 1.0.26 (installed via Rust's Cargo package manager)

Project Anatomy

This example project contains many different files needing to be compiled by the Rust compilier and a C++11 compliant compilier.

Rust code

The Rust code is compiled by the cargo command, and starts in the file src/lib.rs. Any files needing to be compiled, such as src/ffi.rs and src/cxxbridge.rs must be loaded using the pub mod keywords.

Simply add more modules to add Rust functions and structs to the Rust side of the project.

C++ Files

The C++ code is compiled and linked with the Rust code, after the Rust compiler has produced a static library, the C++ compiler then links the Rust and C++ libraries together into a single Shared library (.so on Linux and .dll/.lib on Windows).

Files:

src/lib.cpp
include/mmscenegraph/_cpp.h

Library Header

The include/mmscenegraph.h file defines the functions, data structures and data types from Rust and C++ into a C++ compatible header file.

include/mmscenegraph.h is publically facing and has a C++ namespace mmscenegraph.

The contents of include/mmscenegraph.h combines auto-generated headers, see the next section for details.

Auto-Generated C++ code

Rust source files are parsed by the commands cbindgen and cxxbridge. The commands are used to generate C++ source and header files which can then be used in a C++ compiler.

The details of the cbindgen command is controlled by the cbindgen.toml configuration file, and Rust code in defined in src/ffi.rs.

The cxxbridge command parses the src/cxxbridge.rs file and outputs src/_cxxbridge.cpp and include/_cxxbridge.h files. cxxbridge Can also generate a C++ shim header include/cxx.h to aid in the transition between C++ and Rust functions.

Files:

src/ffi.rs
src/cxxbridge.rs
src/_cxxbridge.cpp
include/cxx.h
include/_cbindgen.h
include/_cxxbridge.h
cbindgen.toml

Build files

This project is built by both cargo (for Rust code) and cmake (for C++ code). To combine the two programs in an easy-to-understand way, the build_linux.bash GNU Bash and build_windows64.bat Windows Batch file are provided.

CMake is used to define the C++ build and must be called after all files have been generated and Rust code has been compiled. CMake 2.8.12 is the minimum supported version, due to backwards compatibility. The configuation file is CMakeLists.txt.

Cargo.toml defines the Rust compiler's dependencies and build process.

Files:

CMakeLists.txt
src/CMakeLists.txt
include/CMakeLists.txt
tests/CMakeLists.txt
Cargo.toml
build_linux.bash
build_windows64.bat

Tests

To ensure everything is working the tests sub-directory contains some example client code using both the cbindgen and cxx functions.

Files:

tests/test_a.cpp (cbindgen tests)
tests/test_b.cpp (cxx tests)

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