Skip to content

Commit

Permalink
move documentation from README.md to lib.rs
Browse files Browse the repository at this point in the history 
so it appears on https://docs.rs and inconsistencies aren't
created between README.md and lib.rs

per discussion in rust-lang#920

The old introductory text in lib.rs has been replaced with
the text from README.md and the introductory paragraph revised.
Otherwise no major changes to the text have been made.
  • Loading branch information
@Be-ing
Be-ing committed Jan 28, 2024
1 parent 4d36cfa commit c2df4e4
Show file tree
Hide file tree
Showing 2 changed files with 195 additions and 237 deletions.
222 changes: 8 additions & 214 deletions README.md
View file
@@ -1,219 +1,13 @@
# cc-rs

A library to compile C/C++/assembly into a Rust library/application.

[Documentation](https://docs.rs/cc)

A simple library meant to be used as a build dependency with Cargo packages in
order to build a set of C/C++ files into a static archive. This crate calls out
to the most relevant compiler for a platform, for example using `cl` on MSVC.

## Using cc-rs

First, you'll want to both add a build script for your crate (`build.rs`) and
also add this crate to your `Cargo.toml` via:

```toml
[build-dependencies]
cc = "1.0"
```

Next up, you'll want to write a build script like so:

```rust,no_run
// build.rs
fn main() {
cc::Build::new()
.file("foo.c")
.file("bar.c")
.compile("foo");
}
```

And that's it! Running `cargo build` should take care of the rest and your Rust
application will now have the C files `foo.c` and `bar.c` compiled into a file
named `libfoo.a`. If the C files contain

```c
void foo_function(void) { ... }
```
and
```c
int32_t bar_function(int32_t x) { ... }
```

you can call them from Rust by declaring them in
your Rust code like so:

```rust,no_run
extern "C" {
fn foo_function();
fn bar_function(x: i32) -> i32;
}
pub fn call() {
unsafe {
foo_function();
bar_function(42);
}
}
fn main() {
// ...
}
```

See [the Rustonomicon](https://doc.rust-lang.org/nomicon/ffi.html) for more details.

## External configuration via environment variables

To control the programs and flags used for building, the builder can set a
number of different environment variables.

* `CFLAGS` - a series of space separated flags passed to compilers. Note that
individual flags cannot currently contain spaces, so doing
something like: `-L=foo\ bar` is not possible.
* `CC` - the actual C compiler used. Note that this is used as an exact
executable name, so (for example) no extra flags can be passed inside
this variable, and the builder must ensure that there aren't any
trailing spaces. This compiler must understand the `-c` flag. For
certain `TARGET`s, it also is assumed to know about other flags (most
common is `-fPIC`).
* `AR` - the `ar` (archiver) executable to use to build the static library.
* `CRATE_CC_NO_DEFAULTS` - the default compiler flags may cause conflicts in
some cross compiling scenarios. Setting this variable
will disable the generation of default compiler
flags.
* `CXX...` - see [C++ Support](#c-support).

Furthermore, projects using this crate may specify custom environment variables
to be inspected, for example via the `Build::try_flags_from_environment`
function. Consult the project’s own documentation or its use of the `cc` crate
for any additional variables it may use.

Each of these variables can also be supplied with certain prefixes and suffixes,
in the following prioritized order:

1. `<var>_<target>` - for example, `CC_x86_64-unknown-linux-gnu`
2. `<var>_<target_with_underscores>` - for example, `CC_x86_64_unknown_linux_gnu`
3. `<build-kind>_<var>` - for example, `HOST_CC` or `TARGET_CFLAGS`
4. `<var>` - a plain `CC`, `AR` as above.

If none of these variables exist, cc-rs uses built-in defaults.

In addition to the above optional environment variables, `cc-rs` has some
functions with hard requirements on some variables supplied by [cargo's
build-script driver][cargo] that it has the `TARGET`, `OUT_DIR`, `OPT_LEVEL`,
and `HOST` variables.

[cargo]: https://doc.rust-lang.org/cargo/reference/build-scripts.html#inputs-to-the-build-script

## Optional features

### Parallel

Currently cc-rs supports parallel compilation (think `make -jN`) but this
feature is turned off by default. To enable cc-rs to compile C/C++ in parallel,
you can change your dependency to:

```toml
[build-dependencies]
cc = { version = "1.0", features = ["parallel"] }
```

By default cc-rs will limit parallelism to `$NUM_JOBS`, or if not present it
will limit it to the number of cpus on the machine. If you are using cargo,
use `-jN` option of `build`, `test` and `run` commands as `$NUM_JOBS`
is supplied by cargo.

## Compile-time Requirements

To work properly this crate needs access to a C compiler when the build script
is being run. This crate does not ship a C compiler with it. The compiler
required varies per platform, but there are three broad categories:

* Unix platforms require `cc` to be the C compiler. This can be found by
installing cc/clang on Linux distributions and Xcode on macOS, for example.
* Windows platforms targeting MSVC (e.g. your target triple ends in `-msvc`)
require Visual Studio to be installed. `cc-rs` attempts to locate it, and
if it fails, `cl.exe` is expected to be available in `PATH`. This can be
set up by running the appropriate developer tools shell.
* Windows platforms targeting MinGW (e.g. your target triple ends in `-gnu`)
require `cc` to be available in `PATH`. We recommend the
[MinGW-w64](https://www.mingw-w64.org/) distribution, which is using the
[Win-builds](http://win-builds.org/) installation system.
You may also acquire it via
[MSYS2](https://www.msys2.org/), as explained [here][msys2-help]. Make sure
to install the appropriate architecture corresponding to your installation of
rustc. GCC from older [MinGW](http://www.mingw.org/) project is compatible
only with 32-bit rust compiler.

[msys2-help]: https://github.com/rust-lang/rust#building-on-windows

## C++ support

`cc-rs` supports C++ libraries compilation by using the `cpp` method on
`Build`:

```rust,no_run
fn main() {
cc::Build::new()
.cpp(true) // Switch to C++ library compilation.
.file("foo.cpp")
.compile("foo");
}
```

For C++ libraries, the `CXX` and `CXXFLAGS` environment variables are used instead of `CC` and `CFLAGS`.

The C++ standard library may be linked to the crate target. By default it's `libc++` for macOS, FreeBSD, and OpenBSD, `libc++_shared` for Android, nothing for MSVC, and `libstdc++` for anything else. It can be changed in one of two ways:

1. by using the `cpp_link_stdlib` method on `Build`:
```rust,no-run
fn main() {
cc::Build::new()
.cpp(true)
.file("foo.cpp")
.cpp_link_stdlib("stdc++") // use libstdc++
.compile("foo");
}
```
2. by setting the `CXXSTDLIB` environment variable.

In particular, for Android you may want to [use `c++_static` if you have at most one shared library](https://developer.android.com/ndk/guides/cpp-support).

Remember that C++ does name mangling so `extern "C"` might be required to enable Rust linker to find your functions.

## CUDA C++ support

`cc-rs` also supports compiling CUDA C++ libraries by using the `cuda` method
on `Build`:

```rust,no_run
fn main() {
cc::Build::new()
// Switch to CUDA C++ library compilation using NVCC.
.cuda(true)
.cudart("static")
// Generate code for Maxwell (GTX 970, 980, 980 Ti, Titan X).
.flag("-gencode").flag("arch=compute_52,code=sm_52")
// Generate code for Maxwell (Jetson TX1).
.flag("-gencode").flag("arch=compute_53,code=sm_53")
// Generate code for Pascal (GTX 1070, 1080, 1080 Ti, Titan Xp).
.flag("-gencode").flag("arch=compute_61,code=sm_61")
// Generate code for Pascal (Tesla P100).
.flag("-gencode").flag("arch=compute_60,code=sm_60")
// Generate code for Pascal (Jetson TX2).
.flag("-gencode").flag("arch=compute_62,code=sm_62")
// Generate code in parallel
.flag("-t0")
.file("bar.cu")
.compile("bar");
}
```
A library for [Cargo build scripts](https://doc.rust-lang.org/cargo/reference/build-scripts.html)
to compile a set of C/C++/assembly/CUDA files into a static archive for Cargo
to link into the crate being built. This crate does not compile code itself;
it calls out to the default compiler for the platform. This crate will
automatically detect situations such as cross compilation and
various environment variables and will build code appropriately.

Refer to the [documentation](https://docs.rs/cc) for detailed usage instructions.

## License

Expand Down

0 comments on commit c2df4e4

Please sign in to comment.