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 <a name="Method-signatures"></a>
 <div class="header">
 <p>
 Previous: <a href="_0040encode.html#g_t_0040encode" accesskey="p" rel="prev">@encode</a>, Up: <a href="Type-encoding.html#Type-encoding" accesskey="u" rel="up">Type encoding</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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 <a name="Method-signatures-1"></a>
 <h4 class="subsection">8.3.3 Method signatures</h4>

 <p>This section documents the encoding of method types, which is rarely
 needed to use Objective-C.  You should skip it at a first reading; the
 runtime provides functions that will work on methods and can walk
 through the list of parameters and interpret them for you.  These
 functions are part of the public &ldquo;API&rdquo; and are the preferred way to
 interact with method signatures from user code.
 </p>
 <p>But if you need to debug a problem with method signatures and need to
 know how they are implemented (i.e., the &ldquo;ABI&rdquo;), read on.
 </p>
 <p>Methods have their &ldquo;signature&rdquo; encoded and made available to the
 runtime.  The &ldquo;signature&rdquo; encodes all the information required to
 dynamically build invocations of the method at runtime: return type
 and arguments.
 </p>
 <p>The &ldquo;signature&rdquo; is a null-terminated string, composed of the following:
 </p>
 <ul>
 <li> The return type, including type qualifiers.  For example, a method
 returning <code>int</code> would have <code>i</code> here.

 </li><li> The total size (in bytes) required to pass all the parameters.  This
 includes the two hidden parameters (the object <code>self</code> and the
 method selector <code>_cmd</code>).

 </li><li> Each argument, with the type encoding, followed by the offset (in
 bytes) of the argument in the list of parameters.

 </li></ul>

 <p>For example, a method with no arguments and returning <code>int</code> would
 have the signature <code>i8@0:4</code> if the size of a pointer is 4.  The
 signature is interpreted as follows: the <code>i</code> is the return type
 (an <code>int</code>), the <code>8</code> is the total size of the parameters in
 bytes (two pointers each of size 4), the <code>@0</code> is the first
 parameter (an object at byte offset <code>0</code>) and <code>:4</code> is the
 second parameter (a <code>SEL</code> at byte offset <code>4</code>).
 </p>
 <p>You can easily find more examples by running the &ldquo;strings&rdquo; program
 on an Objective-C object file compiled by GCC.  You&rsquo;ll see a lot of
 strings that look very much like <code>i8@0:4</code>.  They are signatures
 of Objective-C methods.
 </p>

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 Previous: <a href="_0040encode.html#g_t_0040encode" accesskey="p" rel="prev">@encode</a>, Up: <a href="Type-encoding.html#Type-encoding" accesskey="u" rel="up">Type encoding</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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	<a name="Method-signatures"></a>
	<div class="header">
	<p>
	Previous: <a href="_0040encode.html#g_t_0040encode" accesskey="p" rel="prev">@encode</a>, Up: <a href="Type-encoding.html#Type-encoding" accesskey="u" rel="up">Type encoding</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Method-signatures-1"></a>
	<h4 class="subsection">8.3.3 Method signatures</h4>

	<p>This section documents the encoding of method types, which is rarely
	needed to use Objective-C. You should skip it at a first reading; the
	runtime provides functions that will work on methods and can walk
	through the list of parameters and interpret them for you. These
	functions are part of the public “API” and are the preferred way to
	interact with method signatures from user code.
	</p>
	<p>But if you need to debug a problem with method signatures and need to
	know how they are implemented (i.e., the “ABI”), read on.
	</p>
	<p>Methods have their “signature” encoded and made available to the
	runtime. The “signature” encodes all the information required to
	dynamically build invocations of the method at runtime: return type
	and arguments.
	</p>
	<p>The “signature” is a null-terminated string, composed of the following:
	</p>
	<ul>
	<li> The return type, including type qualifiers. For example, a method
	returning <code>int</code> would have <code>i</code> here.

	</li><li> The total size (in bytes) required to pass all the parameters. This
	includes the two hidden parameters (the object <code>self</code> and the
	method selector <code>_cmd</code>).

	</li><li> Each argument, with the type encoding, followed by the offset (in
	bytes) of the argument in the list of parameters.

	</li></ul>

	<p>For example, a method with no arguments and returning <code>int</code> would
	have the signature <code>i8@0:4</code> if the size of a pointer is 4. The
	signature is interpreted as follows: the <code>i</code> is the return type
	(an <code>int</code>), the <code>8</code> is the total size of the parameters in
	bytes (two pointers each of size 4), the <code>@0</code> is the first
	parameter (an object at byte offset <code>0</code>) and <code>:4</code> is the
	second parameter (a <code>SEL</code> at byte offset <code>4</code>).
	</p>
	<p>You can easily find more examples by running the “strings” program
	on an Objective-C object file compiled by GCC. You’ll see a lot of
	strings that look very much like <code>i8@0:4</code>. They are signatures
	of Objective-C methods.
	</p>

	<hr>
	<div class="header">
	<p>
	Previous: <a href="_0040encode.html#g_t_0040encode" accesskey="p" rel="prev">@encode</a>, Up: <a href="Type-encoding.html#Type-encoding" accesskey="u" rel="up">Type encoding</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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