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| <ol class="chapter"><li class="chapter-item expanded "><a href="introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="requirements.html"><strong aria-hidden="true">2.</strong> Requirements</a></li><li class="chapter-item expanded "><a href="library-usage.html"><strong aria-hidden="true">3.</strong> Library Usage with build.rs</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="tutorial-0.html"><strong aria-hidden="true">3.1.</strong> Tutorial</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="tutorial-1.html"><strong aria-hidden="true">3.1.1.</strong> Add bindgen as a Build Dependency</a></li><li class="chapter-item expanded "><a href="tutorial-2.html"><strong aria-hidden="true">3.1.2.</strong> Create a wrapper.h Header</a></li><li class="chapter-item expanded "><a href="tutorial-3.html" class="active"><strong aria-hidden="true">3.1.3.</strong> Create a build.rs File</a></li><li class="chapter-item expanded "><a href="tutorial-4.html"><strong aria-hidden="true">3.1.4.</strong> Include the Generated Bindings in src/lib.rs</a></li><li class="chapter-item expanded "><a href="tutorial-5.html"><strong aria-hidden="true">3.1.5.</strong> Write a Sanity Test</a></li><li class="chapter-item expanded "><a href="tutorial-6.html"><strong aria-hidden="true">3.1.6.</strong> Publish Your Crate!</a></li></ol></li><li class="chapter-item expanded "><a href="non-system-libraries.html"><strong aria-hidden="true">3.2.</strong> Bindings for non-system libraries</a></li></ol></li><li class="chapter-item expanded "><a href="command-line-usage.html"><strong aria-hidden="true">4.</strong> Command Line Usage</a></li><li class="chapter-item expanded "><a href="customizing-generated-bindings.html"><strong aria-hidden="true">5.</strong> Customizing the Generated Bindings</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="allowlisting.html"><strong aria-hidden="true">5.1.</strong> Allowlisting</a></li><li class="chapter-item expanded "><a href="blocklisting.html"><strong aria-hidden="true">5.2.</strong> Blocklisting</a></li><li class="chapter-item expanded "><a href="opaque.html"><strong aria-hidden="true">5.3.</strong> Treating a Type as an Opaque Blob of Bytes</a></li><li class="chapter-item expanded "><a href="replacing-types.html"><strong aria-hidden="true">5.4.</strong> Replacing One Type with Another</a></li><li class="chapter-item expanded "><a href="nocopy.html"><strong aria-hidden="true">5.5.</strong> Preventing the Derivation of Copy and Clone</a></li><li class="chapter-item expanded "><a href="nodebug.html"><strong aria-hidden="true">5.6.</strong> Preventing the Derivation of Debug</a></li><li class="chapter-item expanded "><a href="nodefault.html"><strong aria-hidden="true">5.7.</strong> Preventing the Derivation of Default</a></li><li class="chapter-item expanded "><a href="must-use-types.html"><strong aria-hidden="true">5.8.</strong> Annotating types with #[must-use]</a></li><li class="chapter-item expanded "><a href="visibility.html"><strong aria-hidden="true">5.9.</strong> Field visibility</a></li><li class="chapter-item expanded "><a href="code-formatting.html"><strong aria-hidden="true">5.10.</strong> Code formatting</a></li></ol></li><li class="chapter-item expanded "><a href="cpp.html"><strong aria-hidden="true">6.</strong> Generating Bindings to C++</a></li><li class="chapter-item expanded "><a href="objc.html"><strong aria-hidden="true">7.</strong> Generating Bindings to Objective-c</a></li><li class="chapter-item expanded "><a href="using-unions.html"><strong aria-hidden="true">8.</strong> Using Unions</a></li><li class="chapter-item expanded "><a href="using-bitfields.html"><strong aria-hidden="true">9.</strong> Using Bitfields</a></li><li class="chapter-item expanded "><a href="using-fam.html"><strong aria-hidden="true">10.</strong> Using Flexible Array Members</a></li><li class="chapter-item expanded "><a href="faq.html"><strong aria-hidden="true">11.</strong> FAQ</a></li></ol> |
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| <h1><a class="header" href="#create-a-buildrs-file" id="create-a-buildrs-file">Create a <code>build.rs</code> File</a></h1> |
| <p>We create a <code>build.rs</code> file in our crate's root. Cargo will pick up on the existence of this file, then compile and execute it before the rest of the crate is built. |
| This can be used to generate code at compile time. |
| And of course in our case, we will be generating Rust FFI |
| bindings to <code>bzip2</code> at compile time. The resulting bindings will be written to |
| <code>$OUT_DIR/bindings.rs</code> where <code>$OUT_DIR</code> is chosen by <code>cargo</code> and is something |
| like <code>./target/debug/build/bindgen-tutorial-bzip2-sys-afc7747d7eafd720/out/</code>.</p> |
| <p>Note that the associated shared object to <code>bz2</code> is <code>libbz2.so</code>. In general, a <code>lib<name>.so</code> should be referenced in the build file by <code><name></code>.</p> |
| <pre><code class="language-rust ignore">use std::env; |
| use std::path::PathBuf; |
| |
| fn main() { |
| // Tell cargo to look for shared libraries in the specified directory |
| println!("cargo:rustc-link-search=/path/to/lib"); |
| |
| // Tell cargo to tell rustc to link the system bzip2 |
| // shared library. |
| println!("cargo:rustc-link-lib=bz2"); |
| |
| // The bindgen::Builder is the main entry point |
| // to bindgen, and lets you build up options for |
| // the resulting bindings. |
| let bindings = bindgen::Builder::default() |
| // The input header we would like to generate |
| // bindings for. |
| .header("wrapper.h") |
| // Tell cargo to invalidate the built crate whenever any of the |
| // included header files changed. |
| .parse_callbacks(Box::new(bindgen::CargoCallbacks::new())) |
| // Finish the builder and generate the bindings. |
| .generate() |
| // Unwrap the Result and panic on failure. |
| .expect("Unable to generate bindings"); |
| |
| // Write the bindings to the $OUT_DIR/bindings.rs file. |
| let out_path = PathBuf::from(env::var("OUT_DIR").unwrap()); |
| bindings |
| .write_to_file(out_path.join("bindings.rs")) |
| .expect("Couldn't write bindings!"); |
| } |
| </code></pre> |
| <p>Now, when we run <code>cargo build</code>, our bindings to <code>bzip2</code> are generated on the |
| fly!</p> |
| <p><a href="https://doc.rust-lang.org/cargo/reference/build-scripts.html">There's more info about <code>build.rs</code> files in the Cargo documentation.</a></p> |
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