{"id":13225,"date":"2022-10-03T10:19:58","date_gmt":"2022-10-03T04:49:58","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-how-to-hold-rust-objects-in-rust-code-created-through-c\/"},"modified":"2022-10-03T10:19:58","modified_gmt":"2022-10-03T04:49:58","slug":"solved-how-to-hold-rust-objects-in-rust-code-created-through-c","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-how-to-hold-rust-objects-in-rust-code-created-through-c\/","title":{"rendered":"[Solved] How to hold Rust objects in Rust code created through C++?"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-62345080\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"62345080\" data-parentid=\"62338832\" data-score=\"2\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<blockquote>\n<p>To achieve that, we need a way to store the instances into a list of some kind, and return the index of the list to C++, so it works like a pointer to a Rust struct.<\/p>\n<\/blockquote>\n<p>I can&#8217;t see why this would be the case. You don&#8217;t need a static list to return pointers from Rust. Simply allocate a <code>Box<\/code> in Rust and return it to the C++ code \u2013 a <code>Box&lt;T&gt;<\/code> with <code>T: Sized<\/code> has <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/doc.rust-lang.org\/beta\/std\/boxed\/index.html#memory-layout\">the same memory layout as a C pointer<\/a>.<\/p>\n<p>As explained in the linked documentation, your code can simply look like this:<\/p>\n<pre class=\"lang-cc prettyprint-override\"><code>\/\/ C++ header\n\n\/\/ Returns ownership to the caller\nextern \"C\" void *foo_new();\n\n\/\/ Borrows mutably. The pointee cannot be changed by a different thread\n\/\/ during the runtime of the function. The argument must be a pointer\n\/\/ allocated with foo_new().\nextern \"C\" void foo_transmogrify(void *);\n\n\/\/ Takes ownership from the caller; no-op when invoked with NULL\nextern \"C\" void foo_delete(void *);\n<\/code><\/pre>\n<pre><code>#[repr(C)]\npub struct Foo {\n    glonk: bool,\n}\n\n#[no_mangle]\npub extern \"C\" fn foo_new() -&gt; Box&lt;Foo&gt; {\n    Box::new(Foo { glonk: false })\n}\n\n#[no_mangle]\npub extern \"C\" fn foo_transmogrify(foo: &amp;mut Foo) {\n    foo.glonk = true;\n}\n\n#[no_mangle]\npub extern \"C\" fn foo_delete(_: Option&lt;Box&lt;Foo&gt;&gt;) {}\n<\/code><\/pre>\n<p>Note that the deallocation function can simply be empty. It will take ownership of the <code>Box<\/code> and implicitly drops it at the end of the function body.<\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">9<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved How to hold Rust objects in Rust code created through C++? <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] To achieve that, we need a way to store the instances into a list of some kind, and return the index of the list to C++, so it works like a pointer to a Rust struct. I can&#8217;t see why this would be the case. You don&#8217;t need a static list to return pointers &#8230; <a title=\"[Solved] How to hold Rust objects in Rust code created through C++?\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-hold-rust-objects-in-rust-code-created-through-c\/\" aria-label=\"More on [Solved] How to hold Rust objects in Rust code created through C++?\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[942],"class_list":["post-13225","post","type-post","status-publish","format-standard","hentry","category-solved","tag-rust"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] How to hold Rust objects in Rust code created through C++? - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-hold-rust-objects-in-rust-code-created-through-c\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] How to hold Rust objects in Rust code created through C++? - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] To achieve that, we need a way to store the instances into a list of some kind, and return the index of the list to C++, so it works like a pointer to a Rust struct. 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