<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><p style="margin: 0px 0px 1em; padding: 0px; border: 0px; font-size: 14px; vertical-align: baseline; clear: both; font-family: Arial, 'Liberation Sans', 'DejaVu Sans', sans-serif; line-height: 17.804800033569336px;">I'm trying to call some C code from OCaml where I need to supply an allocated pointer to my type <code style="margin: 0px; padding: 1px 5px; border: 0px; vertical-align: baseline; background-color: rgb(238, 238, 238); font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, serif; white-space: pre-wrap;">yaml_parser_t</code>. But I'm not sure how I should be allocating a valid pointer. The example code is below.</p><p style="margin: 0px 0px 1em; padding: 0px; border: 0px; font-size: 14px; vertical-align: baseline; clear: both; font-family: Arial, 'Liberation Sans', 'DejaVu Sans', sans-serif; line-height: 17.804800033569336px;">Ideally I'd like to not have to supply a concrete implementation for <code style="margin: 0px; padding: 1px 5px; border: 0px; vertical-align: baseline; background-color: rgb(238, 238, 238); font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, serif; white-space: pre-wrap;">yaml_parser_t</code> as well, since I don't need to inspect it's internals, just pass it into and out of various functions. Plus the description of <span style="background-color: rgb(238, 238, 238); font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, serif; white-space: pre-wrap;">yaml_parser_t</span><span style="line-height: 17.804800033569336px;"> is large and I don't want to spend my time mapping it if I don't have to. I was initially following the time_t example from</span><span style="line-height: 17.804800033569336px;"> </span><a href="https://realworldocaml.org/v1/en/html/foreign-function-interface.html#pointers-and-arrays" rel="nofollow" style="line-height: 17.804800033569336px; margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(74, 107, 130); text-decoration: none; cursor: pointer;">Real World OCaml</a><span style="line-height: 17.804800033569336px;"> </span><span style="line-height: 17.804800033569336px;">but they seem to be using the</span><span style="line-height: 17.804800033569336px;"> </span><code style="line-height: 17.804800033569336px; margin: 0px; padding: 1px 5px; border: 0px; vertical-align: baseline; background-color: rgb(238, 238, 238); font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, serif; white-space: pre-wrap;">time</code><span style="line-height: 17.804800033569336px;"> </span><span style="line-height: 17.804800033569336px;">function to allocate which I don't have here.</span><span style="line-height: 17.804800033569336px;"> </span></p><pre class="lang-ml prettyprint prettyprinted" style="margin-top: 0px; margin-bottom: 10px; padding: 5px; border: 0px; font-size: 14px; vertical-align: baseline; background-color: rgb(238, 238, 238); font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, serif; overflow: auto; width: auto; max-height: 600px; word-wrap: normal; line-height: 17.804800033569336px;"><code style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, serif; white-space: inherit;"><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">open</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> PosixTypes</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">;;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">open</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> Ctypes</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">;;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">open</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> Foreign</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">;;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">type</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> yaml_parser_t </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> unit</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">;;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">let</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> yaml_parser_t </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">:</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> yaml_parser_t typ </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> </span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">void</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">;;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="com" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(128, 128, 128);">(* To get it working in utop, specify the name of the library *)</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">let</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> libyaml </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> Dl</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">.(</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">dlopen </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">~</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">filename</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">:</span><span class="str" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(128, 0, 0);">"libyaml.dylib"</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">~</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">flags</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">:[</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">RTLD_NOW</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">]);;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">let</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> init </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> foreign </span><span class="str" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(128, 0, 0);">"yaml_parser_initialize"</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">(</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">ptr yaml_parser_t </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">@-></span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> returning int</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">);;</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">let</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> make </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">let</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> p_ptr </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> allocate yaml_parser_t </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">(</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">from_voidp yaml_parser</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">)</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> </span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">in</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
</span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">let</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> _ </span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">=</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;"> init p_ptr </span><span class="kwd" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 139);">in</span><span class="pln" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">
p_ptr</span><span class="pun" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: transparent;">;;</span></code></pre><div><br></div><div>How can I allocate a yaml_parser_t without having to map the entire structure in ctypes?</div><div><br></div><div>Thanks</div><div><br></div><div>
<span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px;"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>-----------------------------------------------------</div><div>Tim McGilchrist</div><div><br></div><div><a href="https://twitter.com/lambda_foo">@lambda_foo</a><br><div><a href="https://github.com/tmcgilchrist">http://github.com/tmcgilchrist</a></div></div></div></span></div></span></span>
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