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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"><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" class="active"><strong aria-hidden="true">11.</strong> FAQ</a></li></ol> |
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| <h1><a class="header" href="#frequently-asked-questions" id="frequently-asked-questions">Frequently Asked Questions</a></h1> |
| <!-- START doctoc generated TOC please keep comment here to allow auto update --> |
| <!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE --> |
| <ul> |
| <li><a href="#why-isnt-bindgen-generating-methods-for-this-allowlisted-class">Why isn't <code>bindgen</code> generating methods for this allowlisted class?</a></li> |
| <li><a href="#why-isnt-bindgen-generating-bindings-to-inline-functions">Why isn't <code>bindgen</code> generating bindings to inline functions?</a></li> |
| <li><a href="#does-bindgen-support-the-c-standard-template-library-stl">Does <code>bindgen</code> support the C++ Standard Template Library (STL)?</a></li> |
| <li><a href="#how-to-deal-with-bindgen-generated-padding-fields">How to deal with bindgen generated padding fields?</a></li> |
| <li><a href="#how-to-generate-bindings-for-a-custom-target">How to generate bindings for a custom target?</a></li> |
| </ul> |
| <!-- END doctoc generated TOC please keep comment here to allow auto update --> |
| <h3><a class="header" href="#why-isnt-bindgen-generating-methods-for-this-allowlisted-class" id="why-isnt-bindgen-generating-methods-for-this-allowlisted-class">Why isn't <code>bindgen</code> generating methods for this allowlisted class?</a></h3> |
| <p>Are the methods <code>inline</code> methods, or defined inline in the class? For example:</p> |
| <pre><code class="language-c++">class Dooder { |
| public: |
| // Function defined inline in the class. |
| int example_one() { return 1; } |
| |
| // `inline` function whose definition is supplied later in the header, or in |
| // another header. |
| inline bool example_two(); |
| }; |
| |
| inline bool Dooder::example_two() { |
| return true; |
| } |
| </code></pre> |
| <p>If so, see |
| <a href="#why-isnt-bindgen-generating-bindings-to-inline-functions">"Why isn't <code>bindgen</code> generating bindings to inline functions?"</a></p> |
| <p>If not, consider filing an issue!</p> |
| <h3><a class="header" href="#why-isnt-bindgen-generating-bindings-to-inline-functions" id="why-isnt-bindgen-generating-bindings-to-inline-functions">Why isn't <code>bindgen</code> generating bindings to inline functions?</a></h3> |
| <p>These functions don't typically end up in object files or shared libraries with |
| symbols that we can reliably link to, since they are instead inlined into each |
| of their call sites. Therefore, we don't generate bindings to them, since that |
| creates linking errors.</p> |
| <p>However, if you are compiling the C/C++ yourself (rather than using a system |
| shared library, for example), then you can pass <code>-fkeep-inline-functions</code> or |
| <code>-fno-inline-functions</code> to <code>gcc</code> or <code>clang</code>, and invoke <code>bindgen</code> with either |
| the <code>bindgen::Builder::generate_inline_functions</code> method or the |
| <code>--generate-inline-functions</code> flag.</p> |
| <p>Note that these functions and methods are usually marked inline for a reason: |
| they tend to be hot. The above workaround makes them an out-of-line call, which |
| might not provide acceptable performance.</p> |
| <p>As an alternative, you can invoke <code>bindgen</code> with either the |
| <code>bindgen::Builder::wrap_static_fns</code> method or the <code>--wrap-static-fns</code> flag. |
| Which generates a C source file that can be compiled against the input headers |
| to produce Rust headers for <code>static</code> and <code>static inline</code> functions. See <a href="https://github.com/rust-lang/rust-bindgen/discussions/2405">How to |
| handle <code>static inline</code> functions</a> |
| for further information.</p> |
| <h3><a class="header" href="#does-bindgen-support-the-c-standard-template-library-stl" id="does-bindgen-support-the-c-standard-template-library-stl">Does <code>bindgen</code> support the C++ Standard Template Library (STL)?</a></h3> |
| <p>Sort of. A little. Depends what you mean by "support".</p> |
| <p>Most functions, methods, constructors, and destructors are inline in the |
| STL. That ties our hands when it comes to linking: <a href="#why-isnt-bindgen-generating-bindings-to-inline-functions">"Why isn't <code>bindgen</code> generating bindings to inline functions?"</a></p> |
| <p>As far as generating opaque blobs of bytes with the correct size and alignment, |
| <code>bindgen</code> can do pretty well. This is typically enough to let you use types that |
| transitively contain STL things. We generally recommend marking <code>std::.*</code> as |
| opaque, and then allowlisting only the specific things you need from the library |
| you're binding to that is pulling in STL headers.</p> |
| <h3><a class="header" href="#how-to-deal-with-bindgen-generated-padding-fields" id="how-to-deal-with-bindgen-generated-padding-fields">How to deal with bindgen generated padding fields?</a></h3> |
| <p>Depending the architecture, toolchain versions and source struct, it is |
| possible that bindgen will generate padding fields named <code>__bindgen_padding_N</code>. |
| As these fields might be present when compiling for one architecture but not |
| for an other, you should not initialize these fields manually when initializing |
| the struct. Instead, use the <code>Default</code> trait. You can either enable this when |
| constructing the <code>Builder</code> using the <code>derive_default</code> method, or you can |
| implement this per struct using:</p> |
| <pre><code class="language-rust ignore">impl Default for SRC_DATA { |
| fn default() -> Self { |
| unsafe { std::mem::zeroed() } |
| } |
| } |
| </code></pre> |
| <p>This makes it possible to initialize <code>SRC_DATA</code> by:</p> |
| <pre><code class="language-rust ignore">SRC_DATA { |
| field_a: "foo", |
| field_b: "bar", |
| ..Default::default() |
| } |
| </code></pre> |
| <p>In the case bindgen generates a padding field, then this field will |
| be automatically initialized by <code>..Default::default()</code>.</p> |
| <h3><a class="header" href="#how-to-generate-bindings-for-a-custom-target" id="how-to-generate-bindings-for-a-custom-target">How to generate bindings for a custom target?</a></h3> |
| <p>To generate bindings for a custom target you only need to pass the <code>--target</code> |
| argument to <code>libclang</code>. For example, if you want to generate bindings for the |
| <code>armv7a-none-eabi</code> target using the command line, you need to invoke <code>bindgen</code> |
| like so:</p> |
| <pre><code class="language-bash">$ bindgen <input_headers> -- --target=armv7a-none-eabi |
| </code></pre> |
| <p>If you are using <code>bindgen</code> as a library, you should call |
| <code>builder.clang_arg("--target=armv7a-none-eabi")</code> on your <code>builder</code>.</p> |
| |
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