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  3. <title>BOOST_PP_LIST_AT</title>
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  8. The <b>BOOST_PP_LIST_AT</b> macro extracts an element in a <i>list</i>.
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  10. <h4>Usage</h4>
  11. <div class="code">
  12. <b>BOOST_PP_LIST_AT</b>(<i>list</i>, <i>index</i>)
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  14. <h4>Arguments</h4>
  15. <dl>
  16. <dt>list</dt>
  17. <dd>
  18. The <i>list</i> from which a element is to be extracted.&nbsp;
  19. This <i>list</i> must have at least <i>index</i> + <i>1</i> elements.
  20. </dd>
  21. <dt>index</dt>
  22. <dd>
  23. The zero-based position in the <i>list</i> of the element to be extracted.
  24. </dd>
  25. </dl>
  26. <h4>Remarks</h4>
  27. <div>
  28. Previously, this macro could not be used inside <b>BOOST_PP_WHILE</b>.&nbsp;
  29. There is no longer any such restriction.&nbsp;
  30. It is more efficient, however, to use <b>BOOST_PP_LIST_AT_D</b> in such a situation.
  31. </div>
  32. <h4>See Also</h4>
  33. <ul>
  34. <li><a href="list_at_d.html">BOOST_PP_LIST_AT_D</a></li>
  35. </ul>
  36. <h4>Requirements</h4>
  37. <div>
  38. <b>Header:</b> &nbsp;<a href="../headers/list/at.html">&lt;boost/preprocessor/list/at.hpp&gt;</a>
  39. </div>
  40. <h4>Sample Code</h4>
  41. <div><pre>
  42. #include &lt;<a href="../headers/list/at.html">boost/preprocessor/list/at.hpp</a>&gt;
  43. #define LIST (a, (b, (c, <a href="nil.html">BOOST_PP_NIL</a>)))
  44. <a href="list_at.html">BOOST_PP_LIST_AT</a>(LIST, 0) // expands to a
  45. <a href="list_at.html">BOOST_PP_LIST_AT</a>(LIST, 2) // expands to c
  46. </pre></div>
  47. <hr size="1">
  48. <div style="margin-left: 0px;">
  49. <i>© Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
  50. </br><i>© Copyright Paul Mensonides 2002</i>
  51. </div>
  52. <div style="margin-left: 0px;">
  53. <p><small>Distributed under the Boost Software License, Version 1.0. (See
  54. accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
  55. copy at <a href=
  56. "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
  57. </div>
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