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<title>Structures (libffi: the portable foreign function interface library)</title>
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<div class="subsection" id="Structures">
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<span id="Structures-1"></span><h4 class="subsection">2.3.2 Structures</h4>
<p><code>libffi</code> is perfectly happy passing structures back and forth.
You must first describe the structure to <code>libffi</code> by creating a
new <code>ffi_type</code> object for it.
</p>
<span id="index-ffi_005ftype"></span>
<dl class="def">
<dt id="index-ffi_005ftype-1"><span class="category">Data type: </span><span><strong>ffi_type</strong><a href='#index-ffi_005ftype-1' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>The <code>ffi_type</code> has the following members:
</p><dl compact="compact">
<dt><span><code>size_t size</code></span></dt>
<dd><p>This is set by <code>libffi</code>; you should initialize it to zero.
</p>
</dd>
<dt><span><code>unsigned short alignment</code></span></dt>
<dd><p>This is set by <code>libffi</code>; you should initialize it to zero.
</p>
</dd>
<dt><span><code>unsigned short type</code></span></dt>
<dd><p>For a structure, this should be set to <code>FFI_TYPE_STRUCT</code>.
</p>
</dd>
<dt><span><code>ffi_type **elements</code></span></dt>
<dd><p>This is a ‘<samp>NULL</samp>’-terminated array of pointers to <code>ffi_type</code>
objects. There is one element per field of the struct.
</p>
<p>Note that <code>libffi</code> has no special support for bit-fields. You
must manage these manually.
</p></dd>
</dl>
</dd></dl>
<p>The <code>size</code> and <code>alignment</code> fields will be filled in by
<code>ffi_prep_cif</code> or <code>ffi_prep_cif_var</code>, as needed.
</p>
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