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| <ol class="chapter"><li class="chapter-item expanded "><a href="../index.html"><strong aria-hidden="true">1.</strong> Rust ❤️ C++</a></li><li class="chapter-item expanded "><a href="../concepts.html"><strong aria-hidden="true">2.</strong> Core concepts</a></li><li class="chapter-item expanded "><a href="../tutorial.html"><strong aria-hidden="true">3.</strong> Tutorial</a></li><li class="chapter-item expanded "><a href="../context.html"><strong aria-hidden="true">4.</strong> Other Rust–C++ interop tools</a></li><li class="chapter-item expanded "><a href="../building.html"><strong aria-hidden="true">5.</strong> Multi-language build system options</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../build/cargo.html"><strong aria-hidden="true">5.1.</strong> Cargo</a></li><li class="chapter-item expanded "><a href="../build/bazel.html"><strong aria-hidden="true">5.2.</strong> Bazel or Buck2</a></li><li class="chapter-item expanded "><a href="../build/cmake.html"><strong aria-hidden="true">5.3.</strong> CMake</a></li><li class="chapter-item expanded "><a href="../build/other.html"><strong aria-hidden="true">5.4.</strong> More...</a></li></ol></li><li class="chapter-item expanded "><a href="../reference.html"><strong aria-hidden="true">6.</strong> Reference: the bridge module</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../extern-rust.html"><strong aria-hidden="true">6.1.</strong> extern "Rust"</a></li><li class="chapter-item expanded "><a href="../extern-c++.html"><strong aria-hidden="true">6.2.</strong> extern "C++"</a></li><li class="chapter-item expanded "><a href="../shared.html"><strong aria-hidden="true">6.3.</strong> Shared types</a></li><li class="chapter-item expanded "><a href="../attributes.html"><strong aria-hidden="true">6.4.</strong> Attributes</a></li><li class="chapter-item expanded "><a href="../async.html"><strong aria-hidden="true">6.5.</strong> Async functions</a></li><li class="chapter-item expanded "><a href="../binding/result.html"><strong aria-hidden="true">6.6.</strong> Error handling</a></li></ol></li><li class="chapter-item expanded "><a href="../bindings.html"><strong aria-hidden="true">7.</strong> Reference: built-in bindings</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../binding/string.html"><strong aria-hidden="true">7.1.</strong> String — rust::String</a></li><li class="chapter-item expanded "><a href="../binding/str.html"><strong aria-hidden="true">7.2.</strong> &str — rust::Str</a></li><li class="chapter-item expanded "><a href="../binding/slice.html"><strong aria-hidden="true">7.3.</strong> &[T], &mut [T] — rust::Slice<T></a></li><li class="chapter-item expanded "><a href="../binding/cxxstring.html"><strong aria-hidden="true">7.4.</strong> CxxString — std::string</a></li><li class="chapter-item expanded "><a href="../binding/box.html"><strong aria-hidden="true">7.5.</strong> Box<T> — rust::Box<T></a></li><li class="chapter-item expanded "><a href="../binding/uniqueptr.html"><strong aria-hidden="true">7.6.</strong> UniquePtr<T> — std::unique_ptr<T></a></li><li class="chapter-item expanded "><a href="../binding/sharedptr.html"><strong aria-hidden="true">7.7.</strong> SharedPtr<T> — std::shared_ptr<T></a></li><li class="chapter-item expanded "><a href="../binding/vec.html"><strong aria-hidden="true">7.8.</strong> Vec<T> — rust::Vec<T></a></li><li class="chapter-item expanded "><a href="../binding/cxxvector.html"><strong aria-hidden="true">7.9.</strong> CxxVector<T> — std::vector<T></a></li><li class="chapter-item expanded "><a href="../binding/rawptr.html" class="active"><strong aria-hidden="true">7.10.</strong> *mut T, *const T raw pointers</a></li><li class="chapter-item expanded "><a href="../binding/fn.html"><strong aria-hidden="true">7.11.</strong> Function pointers</a></li><li class="chapter-item expanded "><a href="../binding/result.html"><strong aria-hidden="true">7.12.</strong> Result<T></a></li></ol></li><li class="part-title"><a href="https://github.com/dtolnay/cxx"><i class="fa fa-github"></i>https://github.com/dtolnay/cxx</a></li></ol> |
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| <h1 id="mut-t-const-t"><a class="header" href="#mut-t-const-t">*mut T, *const T</a></h1> |
| <p>Generally you should use references (<code class="hljs">&mut T</code>, <code class="hljs">&T</code>) or <a href="uniqueptr.html">std::unique_ptr<T></a> |
| where possible over raw pointers, but raw pointers are available too as an |
| unsafe fallback option.</p> |
| <h3 id="restrictions"><a class="header" href="#restrictions">Restrictions:</a></h3> |
| <p>Extern functions and function pointers taking a raw pointer as an argument must |
| be declared <code class="hljs">unsafe fn</code> i.e. unsafe to call. The same does not apply to |
| functions which only <em>return</em> a raw pointer, though presumably doing anything |
| useful with the returned pointer is going to involve unsafe code elsewhere |
| anyway.</p> |
| <h2 id="example"><a class="header" href="#example">Example</a></h2> |
| <p>This example illustrates making a Rust call to a canonical C-style <code class="hljs">main</code> |
| signature involving <code class="hljs">char *argv[]</code>.</p> |
| <pre><code class="hidelines hide-boring hljs"><span class="hljs-comment">// include/args.h</span> |
| |
| <span class="hljs-meta">#<span class="hljs-meta-keyword">pragma</span> once</span> |
| |
| <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">parseArgs</span><span class="hljs-params">(<span class="hljs-keyword">int</span> argc, <span class="hljs-keyword">char</span> *argv[])</span></span>; |
| </code></pre> |
| <pre><code class="hidelines hide-boring hljs"><span class="hljs-comment">// src/args.cc</span> |
| |
| <span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">"example/include/args.h"</span></span> |
| <span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string"><iostream></span></span> |
| |
| <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">parseArgs</span><span class="hljs-params">(<span class="hljs-keyword">int</span> argc, <span class="hljs-keyword">char</span> *argv[])</span> </span>{ |
| <span class="hljs-built_in">std</span>::<span class="hljs-built_in">cout</span> << argc << <span class="hljs-built_in">std</span>::<span class="hljs-built_in">endl</span>; |
| <span class="hljs-keyword">for</span> (<span class="hljs-keyword">int</span> i = <span class="hljs-number">0</span>; i < argc; i++) { |
| <span class="hljs-built_in">std</span>::<span class="hljs-built_in">cout</span> << <span class="hljs-string">'"'</span> << argv[i] << <span class="hljs-string">'"'</span> << <span class="hljs-built_in">std</span>::<span class="hljs-built_in">endl</span>; |
| } |
| } |
| </code></pre> |
| <pre><code class="noplayground hidelines hide-boring hljs"><span class="hljs-comment">// src/main.rs</span> |
| |
| <span class="hljs-keyword">use</span> std::env; |
| <span class="hljs-keyword">use</span> std::ffi::CString; |
| <span class="hljs-keyword">use</span> std::os::raw::c_char; |
| <span class="hljs-keyword">use</span> std::os::unix::ffi::OsStrExt; |
| <span class="hljs-keyword">use</span> std::ptr; |
| |
| <span class="hljs-meta">#[cxx::bridge]</span> |
| <span class="hljs-keyword">mod</span> ffi { |
| <span class="hljs-keyword">extern</span> <span class="hljs-string">"C++"</span> { |
| include!(<span class="hljs-string">"example/include/args.h"</span>); |
| |
| <span class="hljs-keyword">unsafe</span> <span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">parseArgs</span></span>(argc: <span class="hljs-built_in">i32</span>, argv: *<span class="hljs-keyword">mut</span> *<span class="hljs-keyword">mut</span> c_char); |
| } |
| } |
| |
| <span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">main</span></span>() { |
| <span class="hljs-comment">// Convert from OsString to nul-terminated CString, truncating each argument</span> |
| <span class="hljs-comment">// at the first inner nul byte if present.</span> |
| <span class="hljs-keyword">let</span> args: <span class="hljs-built_in">Vec</span><CString> = env::args_os() |
| .map(|os_str| { |
| <span class="hljs-keyword">let</span> bytes = os_str.as_bytes(); |
| CString::new(bytes).unwrap_or_else(|nul_error| { |
| <span class="hljs-keyword">let</span> nul_position = nul_error.nul_position(); |
| <span class="hljs-keyword">let</span> <span class="hljs-keyword">mut</span> bytes = nul_error.into_vec(); |
| bytes.truncate(nul_position); |
| CString::new(bytes).unwrap() |
| }) |
| }) |
| .collect(); |
| |
| <span class="hljs-comment">// Convert from Vec<CString> of owned strings to Vec<*mut c_char> of</span> |
| <span class="hljs-comment">// borrowed string pointers.</span> |
| <span class="hljs-comment">//</span> |
| <span class="hljs-comment">// Once extern type stabilizes (https://github.com/rust-lang/rust/issues/43467)</span> |
| <span class="hljs-comment">// and https://internals.rust-lang.org/t/pre-rfc-make-cstr-a-thin-pointer/6258</span> |
| <span class="hljs-comment">// is implemented, and CStr pointers become thin, we can sidestep this step</span> |
| <span class="hljs-comment">// by accumulating the args as Vec<Box<CStr>> up front, then simply casting</span> |
| <span class="hljs-comment">// from *mut [Box<CStr>] to *mut [*mut CStr] to *mut *mut c_char.</span> |
| <span class="hljs-keyword">let</span> argc = args.len(); |
| <span class="hljs-keyword">let</span> <span class="hljs-keyword">mut</span> argv: <span class="hljs-built_in">Vec</span><*<span class="hljs-keyword">mut</span> c_char> = <span class="hljs-built_in">Vec</span>::with_capacity(argc + <span class="hljs-number">1</span>); |
| <span class="hljs-keyword">for</span> arg <span class="hljs-keyword">in</span> &args { |
| argv.push(arg.as_ptr() <span class="hljs-keyword">as</span> *<span class="hljs-keyword">mut</span> c_char); |
| } |
| argv.push(ptr::null_mut()); <span class="hljs-comment">// Nul terminator.</span> |
| |
| <span class="hljs-keyword">unsafe</span> { |
| ffi::parseArgs(argc <span class="hljs-keyword">as</span> <span class="hljs-built_in">i32</span>, argv.as_mut_ptr()); |
| } |
| |
| <span class="hljs-comment">// The CStrings go out of scope here. C function must not have held on to</span> |
| <span class="hljs-comment">// the pointers beyond this point.</span> |
| }</code></pre> |
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