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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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