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https://github.com/hywan/inline-c-rs
Write and execute C code inside Rust.
https://github.com/hywan/inline-c-rs
c rust rust-library
Last synced: 8 days ago
JSON representation
Write and execute C code inside Rust.
- Host: GitHub
- URL: https://github.com/hywan/inline-c-rs
- Owner: Hywan
- License: bsd-3-clause
- Created: 2020-10-05T13:44:51.000Z (about 4 years ago)
- Default Branch: master
- Last Pushed: 2024-10-08T07:33:50.000Z (about 1 month ago)
- Last Synced: 2024-10-17T15:43:45.027Z (21 days ago)
- Topics: c, rust, rust-library
- Language: Rust
- Homepage:
- Size: 178 KB
- Stars: 149
- Watchers: 6
- Forks: 19
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- License: LICENSE.md
Awesome Lists containing this project
README
inline-c
[](https://crates.io/crates/inline-c)
[](https://docs.rs/inline-c)
`inline-c` is a small crate that allows a user to write C (including
C++) code inside Rust. Both environments are strictly sandboxed: it is
non-obvious for a value to cross the boundary. The C code is
transformed into a string which is written in a temporary file. This
file is then compiled into an object file, that is finally
executed. It is possible to run assertions about the execution of the
C program.
The primary goal of `inline-c` is to ease the testing of a C API of a
Rust program (generated with
[`cbindgen`](https://github.com/eqrion/cbindgen/) for example). Note
that it's not tied to a Rust program exclusively, it's just its
initial reason to live.
## Install
Add the following lines to your `Cargo.toml` file:
```toml
[dev-dependencies]
inline-c = "0.1"
```
## Documentation
The `assert_c` and `assert_cxx` macros live in the `inline-c-macro`
crate, but are re-exported in this crate for the sake of simplicity.
Being able to write C code directly in Rust offers nice opportunities,
like having C examples inside the Rust documentation that are
executable and thus tested (with `cargo test --doc`). Let's dig into
some examples.
### Basic usage
The following example is super basic: C prints `Hello, World!` on the
standard output, and Rust asserts that.
```rust
use inline_c::assert_c;
fn test_stdout() {
(assert_c! {
#include
int main() {
printf("Hello, World!");
return 0;
}
})
.success()
.stdout("Hello, World!");
}
```
Or with a C++ program:
```rust
use inline_c::assert_cxx;
fn test_cxx() {
(assert_cxx! {
#include
using namespace std;
int main() {
cout << "Hello, World!";
return 0;
}
})
.success()
.stdout("Hello, World!");
}
```
The `assert_c` and `assert_cxx` macros return a `Result>`. See `Assert` to learn more about the possible
assertions.
The following example tests the returned value:
```rust
use inline_c::assert_c;
fn test_result() {
(assert_c! {
int main() {
int x = 1;
int y = 2;
return x + y;
}
})
.failure()
.code(3);
}
```
### Environment variables
It is possible to define environment variables for the execution of
the given C program. The syntax is using the special `#inline_c_rs` C
directive with the following syntax:
```c
#inline_c_rs : ""
```
Please note the double quotes around the variable value.
```rust
use inline_c::assert_c;
fn test_environment_variable() {
(assert_c! {
#inline_c_rs FOO: "bar baz qux"
#include
#include
int main() {
const char* foo = getenv("FOO");
if (NULL == foo) {
return 1;
}
printf("FOO is set to `%s`", foo);
return 0;
}
})
.success()
.stdout("FOO is set to `bar baz qux`");
}
```
#### Meta environment variables
Using the `#inline_c_rs` C directive can be repetitive if one needs to
define the same environment variable again and again. That's why meta
environment variables exist. They have the following syntax:
```sh
INLINE_C_RS_=
```
It is usually best to define them in [a `build.rs`
script](https://doc.rust-lang.org/cargo/reference/build-scripts.html)
for example. Let's see it in action with a tiny example:
```rust
use inline_c::assert_c;
use std::env::{set_var, remove_var};
fn test_meta_environment_variable() {
set_var("INLINE_C_RS_FOO", "bar baz qux");
(assert_c! {
#include
#include
int main() {
const char* foo = getenv("FOO");
if (NULL == foo) {
return 1;
}
printf("FOO is set to `%s`", foo);
return 0;
}
})
.success()
.stdout("FOO is set to `bar baz qux`");
remove_var("INLINE_C_RS_FOO");
}
```
Note: If you have multiple inline C tests that use the same environment
variables, you may see flakiness in test runs because by default `cargo test`
runs tests parallely. This problem can occur even if your tests are removing
the environment variables during teardown. To fix this, you can do either
of the following:
- Use unique environment variable names for each test
- (Not recommended for Production) Run the tests serially instead of parallely.
You can use the following command: `cargo test -- --test-threads=1`
#### `CFLAGS`, `CPPFLAGS`, `CXXFLAGS` and `LDFLAGS`
Some classical `Makefile` variables like `CFLAGS`, `CPPFLAGS`,
`CXXFLAGS` and `LDFLAGS` are understood by `inline-c` and consequently
have a special treatment. Their values are added to the appropriate
compilers when the C code is compiled and linked into an object file.
Pro tip: Let's say we have a Rust crate named `foo`, and it exports a
C API. It is possible to define `CFLAGS` and `LDFLAGS` as follow to
correctly compile and link all the C codes to the Rust `libfoo` shared
object by writing this in a `build.rs` script (it is assumed that
`libfoo` lands in the `target//` directory, and that `foo.h`
lands in the root directory):
```rust
use std::{env, path::PathBuf};
fn main() {
let include_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
let mut shared_object_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
shared_object_dir.push("target");
shared_object_dir.push(env::var("PROFILE").unwrap());
let shared_object_dir = shared_object_dir.as_path().to_string_lossy();
// The following options mean:
//
// * `-I`, add `include_dir` to include search path,
// * `-L`, add `shared_object_dir` to library search path,
// * `-D_DEBUG`, enable debug mode to enable `assert.h`.
println!(
"cargo:rustc-env=INLINE_C_RS_CFLAGS=-I{I} -L{L} -D_DEBUG",
I = include_dir,
L = shared_object_dir.clone(),
);
// Here, we pass the fullpath to the shared object with
// `LDFLAGS`.
println!(
"cargo:rustc-env=INLINE_C_RS_LDFLAGS={shared_object_dir}/{lib}",
shared_object_dir = shared_object_dir,
lib = if cfg!(target_os = "windows") {
"foo.dll".to_string()
} else if cfg!(target_os = "macos") {
"libfoo.dylib".to_string()
} else {
"libfoo.so".to_string()
}
);
}
```
_Et voilà !_ Now run `cargo build --release` (to generate the
shared objects) and then `cargo test --release` to see it in
action.
### Using `inline-c` inside Rust documentation
Since it is now possible to write C code inside Rust, it is
consequently possible to write C examples, that are:
1. Part of the Rust documentation with `cargo doc`, and
2. Tested with all the other Rust examples with `cargo test --doc`.
Yes. Testing C code with `cargo test --doc`. How _fun_ is that? No
trick needed. One can write:
```rust
/// Blah blah blah.
///
/// # Example
///
/// ```rust
/// # use inline_c::assert_c;
/// #
/// # fn main() {
/// # (assert_c! {
/// #include
///
/// int main() {
/// printf("Hello, World!");
///
/// return 0;
/// }
/// # })
/// # .success()
/// # .stdout("Hello, World!");
/// # }
/// ```
pub extern "C" fn some_function() {}
```
which will compile down into something like this:
```c
int main() {
printf("Hello, World!");
return 0;
}
```
Notice that this example above is actually Rust code, with C code
inside. Only the C code is printed, due to the `#` hack of `rustdoc`,
but this example is a valid Rust example, and is fully tested!
There is one minor caveat though: the highlighting. The Rust set of
rules are applied, rather than the C ruleset. [See this issue on
`rustdoc` to follow the
fix](https://github.com/rust-lang/rust/issues/78917).
### C macros
C macros with the `#define` directive is supported only with Rust
nightly. One can write:
```rust,ignore
use inline_c::assert_c;
fn test_c_macro() {
(assert_c! {
#define sum(a, b) ((a) + (b))
int main() {
return !(sum(1, 2) == 3);
}
})
.success();
}
```
Note that multi-lines macros don't work! That's because the `\` symbol
is consumed by the Rust lexer. The best workaround is to define the
macro in another `.h` file, and to include it with the `#include`
directive.
## License
`BSD-3-Clause`, see `LICENSE.md`.