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<h3 class="section">6.48 Offsetof</h3>

<p><a name="index-g_t_005f_005fbuiltin_005foffsetof-2612"></a>
GCC implements for both C and C++ a syntactic extension to implement
the <code>offsetof</code> macro.

<pre class="smallexample">     primary:
             "__builtin_offsetof" "(" <code>typename</code> "," offsetof_member_designator ")"
     
     offsetof_member_designator:
               <code>identifier</code>
             | offsetof_member_designator "." <code>identifier</code>
             | offsetof_member_designator "[" <code>expr</code> "]"
</pre>
 <p>This extension is sufficient such that

<pre class="smallexample">     #define offsetof(<var>type</var>, <var>member</var>)  __builtin_offsetof (<var>type</var>, <var>member</var>)
</pre>
 <p>is a suitable definition of the <code>offsetof</code> macro.  In C++, <var>type</var>
may be dependent.  In either case, <var>member</var> may consist of a single
identifier, or a sequence of member accesses and array references.

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