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| <h1 id="interoperability"><a class="header" href="#interoperability">Interoperability</a></h1> |
| <p>Interoperability between Rust and C code is always dependent |
| on transforming data between the two languages. |
| For this purpose, there is a dedicated module |
| in the <code>stdlib</code> called |
| <a href="https://doc.rust-lang.org/std/ffi/index.html"><code>std::ffi</code></a>.</p> |
| <p><code>std::ffi</code> provides type definitions for C primitive types, |
| such as <code>char</code>, <code>int</code>, and <code>long</code>. |
| It also provides some utility for converting more complex |
| types such as strings, mapping both <code>&str</code> and <code>String</code> |
| to C types that are easier and safer to handle.</p> |
| <p>As of Rust 1.30, |
| functionalities of <code>std::ffi</code> are available |
| in either <code>core::ffi</code> or <code>alloc::ffi</code> |
| depending on whether or not memory allocation is involved. |
| The <a href="https://crates.io/crates/cty"><code>cty</code></a> crate and the <a href="https://crates.io/crates/cstr_core"><code>cstr_core</code></a> crate |
| also offer similar functionalities.</p> |
| <div class="table-wrapper"><table><thead><tr><th>Rust type</th><th>Intermediate</th><th>C type</th></tr></thead><tbody> |
| <tr><td><code>String</code></td><td><code>CString</code></td><td><code>char *</code></td></tr> |
| <tr><td><code>&str</code></td><td><code>CStr</code></td><td><code>const char *</code></td></tr> |
| <tr><td><code>()</code></td><td><code>c_void</code></td><td><code>void</code></td></tr> |
| <tr><td><code>u32</code> or <code>u64</code></td><td><code>c_uint</code></td><td><code>unsigned int</code></td></tr> |
| <tr><td>etc</td><td>...</td><td>...</td></tr> |
| </tbody></table> |
| </div> |
| <p>A value of a C primitive type can be used |
| as one of the corresponding Rust type and vice versa, |
| since the former is simply a type alias of the latter. |
| For example, the following code compiles on platforms |
| where <code>unsigned int</code> is 32-bit long.</p> |
| <pre><code class="language-rust ignore">fn foo(num: u32) { |
| let c_num: c_uint = num; |
| let r_num: u32 = c_num; |
| }</code></pre> |
| <h2 id="interoperability-with-other-build-systems"><a class="header" href="#interoperability-with-other-build-systems">Interoperability with other build systems</a></h2> |
| <p>A common requirement for including Rust in your embedded project is combining |
| Cargo with your existing build system, such as make or cmake.</p> |
| <p>We are collecting examples and use cases for this on our issue tracker in |
| <a href="https://github.com/rust-embedded/book/issues/61">issue #61</a>.</p> |
| <h2 id="interoperability-with-rtoss"><a class="header" href="#interoperability-with-rtoss">Interoperability with RTOSs</a></h2> |
| <p>Integrating Rust with an RTOS such as FreeRTOS or ChibiOS is still a work in |
| progress; especially calling RTOS functions from Rust can be tricky.</p> |
| <p>We are collecting examples and use cases for this on our issue tracker in |
| <a href="https://github.com/rust-embedded/book/issues/62">issue #62</a>.</p> |
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