Cpp2Rust

Cpp2Rust translates C++ to fully safe Rust automatically. It is a syntax-driven translator based on clang's AST.

Cpp2Rust's algorithm is described in the paper Cpp2Rust: Automatic Translation of C++ to Safe Rust published at PLDI 2026.

Overview

Cpp2Rust first parses the input C++ file(s) with clang and produces an AST. It then traverses the AST and emits Rust code as strings, inserting calls to the libcc2rs runtime library where needed (e.g., for raw pointer semantics). Finally, the Rust code is pretty-printed using rustfmt to a single .rs file.

By default the reference counting model is used, which produces fully safe Rust. A generator of unsafe Rust is also available through the --model=unsafe command line argument for debugging and performance comparisons.

Runtime library (libcc2rs)

The generated code relies on a runtime library designed to simplify the translation process. C pointers are converted into the Ptr<T> type provided by libcc2rs. Ptr<T> models C pointer semantics, including null, arithmetic, and aliasing, while satisfying Rust's borrow checker through checked run-time operations.

Requirements

On Ubuntu, install the required dependencies with:

sudo apt install libclang-22-dev clang++-22 ninja-build cmake python3-tomli
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain 1.94.0

Build

mkdir build
cd build
cmake -GNinja ..
ninja
ninja check

Run

Translate a single file

./build/cpp2rust/cpp2rust --file=<file>.cpp -o=<file>.rs

By default, the reference couting model is used (fully safe output). To generate unsafe Rust instead:

./build/cpp2rust/cpp2rust --file=<file>.cpp -o=<file>.rs --model=unsafe

Minimal example. Given hello.cpp:

#include <cstdio>
int main() {
  printf("hello world\n");
  return 0;
}

Running ./build/cpp2rust/cpp2rust --file=hello.cpp -o=hello.rs produces:

pub fn main() {
    std::process::exit(main_0());
}
fn main_0() -> i32 {
    println!("hello world");
    return 0;
}

Compile and run with:

rustc hello.rs -L ../libcc2rs/target/debug
./hello

Translate a whole program

First generate a compile_commands.json for your project. With CMake this is one extra flag:

cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON ..

Then run:

./build/cpp2rust/cpp2rust --dir=<dir> -o <output>.rs

<dir> must be the directory that contains compile_commands.json.

Test Suite

# Run all tests except benchmarks
ninja check

# Run only the unit tests
ninja check-unit

# Run libcc2rs unit tests
ninja check-libcc2rs

# Run benchmarks (compile & execute)
ninja check-benchmarks

# Check benchmark output without executing binaries
SKIP_RUN=1 ninja check-benchmarks

# Regenerate and check if the IR for the rules changed
ninja check-rules

# Regenerate expected output for unit tests after intentional changes
REPLACE_EXPECTED=1 ninja check-unit