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* Fix evaluateConstantInt

Ensure we set the value when there is one, instead of when there isn't.

* Use getIntegerConstantExpr in evaluateConstantInt

isIntegerConstantExpr no longer retrieves the constant from an expr in
LLVM 12, so we need to call our helper to do that to preserve the old

Co-authored-by: Stephen Crane <>

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C2Rust helps you migrate C99-compliant code to Rust. The translator (or transpiler) produces unsafe Rust code that closely mirrors the input C code. The primary goal of the translator is to preserve functionality; test suites should continue to pass after translation. Generating safe and idiomatic Rust code from C ultimately requires manual effort. However, we are building a scriptable refactoring tool that reduces the tedium of doing so. You can also cross-check the translated code against the original (tutorial).

Here's the big picture:

C2Rust overview

To learn more, check out our RustConf'18 talk on YouTube and try the C2Rust translator online at


To learn more about using and developing C2Rust, check out the manual. The manual is still a work-in-progress, so if you can't find something please let us know.



C2Rust requires LLVM 6 or later with its corresponding clang compiler and libraries. Python 3.4 or later, CMake 3.4.3 or later, and openssl (1.0) are also required. These prerequisites may be installed with the following commands, depending on your platform:

  • Ubuntu 16.04, 18.04 & 18.10:

      apt install build-essential llvm-6.0 clang-6.0 libclang-6.0-dev cmake libssl-dev pkg-config python3
  • Arch Linux:

      pacman -S base-devel llvm clang cmake openssl python
  • NixOS / nix:

  • OS X: XCode command-line tools and recent LLVM (we recommend the Homebrew version) are required.

      xcode-select --install
      brew install llvm python3 cmake openssl

Finally, installing the correct nightly Rust compiler with Rustup is required on all platforms. You will also need to add rustfmt and rustc-dev:

rustup install nightly-2019-12-05
rustup component add --toolchain nightly-2019-12-05 rustfmt rustc-dev

Installing from

cargo +nightly-2019-12-05 install c2rust

On OS X with Homebrew LLVM, you need to point the build system at the LLVM installation as follows:

LLVM_CONFIG_PATH=/usr/local/opt/llvm/bin/llvm-config cargo +nightly-2019-12-05 install c2rust

On Linux with Linuxbrew LLVM, you need to point the build system at the LLVM installation as follows:

LLVM_CONFIG_PATH=/home/linuxbrew/.linuxbrew/opt/llvm/bin/llvm-config cargo +nightly-2019-12-05 install c2rust    

Note: adjust LLVM_CONFIG_PATH accordingly if Linuxbrew was installed to your home directory.

On Gentoo, you need to point the build system to the location of and llvm-config as follows:

LLVM_CONFIG_PATH=/path/to/llvm-config LIBCLANG_PATH=/path/to/ cargo +nightly-2019-12-05 install c2rust 

If you have trouble with building and installing, or want to build from the latest master, the developer docs provide more details on the build system.

Installing from Git

If you'd like to check our recently developed features or you urgently require a bugfixed version of c2rust you can install it directly from Git:

cargo +nightly-2019-12-05 install --git c2rust

Please note that the master branch is under constant development and you may expirience issues or crashes.

You should also set LLVM_CONFIG_PATH accordingly if required as described above.

Translating C to Rust

To translate C files specified in compile_commands.json (see below), run the c2rust tool with the transpile subcommand:

c2rust transpile compile_commands.json

(The c2rust refactor tool is also available for refactoring Rust code, see refactoring).

The translator requires the exact compiler commands used to build the C code. This information is provided via a compilation database file named compile_commands.json. (Read more about compilation databases here and here). Many build systems can automatically generate this file; we show a few examples below.

Once you have a compile_commands.json file describing the C build, translate the C code to Rust with the following command:

c2rust transpile path/to/compile_commands.json

To generate a Cargo.toml template for a Rust library, add the -e option:

c2rust transpile --emit-build-files path/to/compile_commands.json

To generate a Cargo.toml template for a Rust binary, do this:

c2rust transpile --binary myprog path/to/compile_commands.json

Where --binary myprog tells the transpiler to use the main method from as the entry point for a binary.

The translated Rust files will not depend directly on each other like normal Rust modules. They will export and import functions through the C API. These modules can be compiled together into a single static Rust library or binary.

There are several known limitations in this translator. The translator will emit a warning and attempt to skip function definitions that cannot be translated.

Generating compile_commands.json files

The compile_commands.json file can be automatically created using either cmake, intercept-build, or bear.

It may be a good idea to remove optimizations(-OX) from the compile commands file, as there are optimization builtins which we do not support translating.

... with cmake

When creating the initial build directory with cmake specify -DCMAKE_EXPORT_COMPILE_COMMANDS=1. This only works on projects configured to be built by cmake. This works on Linux and MacOS.


... with intercept-build

intercept-build (part of the scan-build tool) is recommended for non-cmake projects. intercept-build is bundled with clang under tools/scan-build-py but a standalone version can be easily installed via PIP with:

pip install scan-build


intercept-build <build command>

You can also use intercept-build to generate a compilation database for compiling a single C file, for example:

intercept-build sh -c "cc program.c"

... with bear (linux only)

If you have bear installed, it can be used similarly to intercept-build:

bear <build command>


To report issues with translation or refactoring, please use our Issue Tracker.

To reach the development team, join our discord channel or email us at


I translated code on platform X but it didn't work correctly on platform Y

We run the C preprocessor before translation to Rust. This specializes the code to the host platform. For this reason, we do not support cross compiling translated code at the moment.

What platforms can C2Rust be run on?

The translator and refactoring tool support both macOS and Linux. Other features, such as cross checking the functionality between C and Rust code, are currently limited to Linux hosts.

Acknowledgements and Licensing

This material is available under the BSD-3 style license as found in the LICENSE file.

The C2Rust translator is inspired by Jamey Sharp's Corrode translator. We rely on Emscripten's Relooper algorithm to translate arbitrary C control flows.

This material is based upon work supported by the United States Air Force and DARPA under Contract No. FA8750-15-C-0124. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the United States Air Force and DARPA. Distribution Statement A, “Approved for Public Release, Distribution Unlimited.”