| [29] | 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> |
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| 3 | <html> |
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| 4 | <head> |
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| 5 | <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> |
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| 6 | <title>Boost.Range Introduction </title> |
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| 7 | <link rel="stylesheet" href="style.css" type="text/css"> |
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| 8 | </head> |
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| 9 | |
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| 10 | <body> |
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| 11 | |
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| 12 | <table border="0" > |
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| 13 | <tr> |
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| 14 | <td ><img src="../../../boost.png" border="0" ></td> |
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| 15 | <td ><h1 align="center">Boost.Range</h1></td> |
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| 16 | </tr> |
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| 17 | </table> |
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| 18 | |
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| 19 | <h2>Introduction</h2> |
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| 20 | <p> |
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| 21 | Generic algorithms have so far been specified in terms of two or more |
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| 22 | iterators. Two iterators would together form a range of values that the |
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| 23 | algorithm could work on. This leads to a very general interface, but also |
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| 24 | to a somewhat clumsy use of the algorithms with redundant specification |
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| 25 | of container names. Therefore we would like to raise the abstraction level |
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| 26 | for algorithms so they specify their interface in terms of <a |
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| 27 | href=range.html>Ranges</a> as much as possible. |
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| 28 | </p> |
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| 29 | |
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| 30 | <p> |
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| 31 | The most common form of ranges we are used to work with is standard library |
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| 32 | containers. However, one |
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| 33 | often finds it desirable to extend that code to work with other types that |
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| 34 | offer |
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| 35 | enough functionality to satisfy the needs of the generic code |
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| 36 | <i>if a suitable layer of indirection is applied </i>. For |
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| 37 | example, raw arrays are often suitable for use with generic code that |
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| 38 | works with containers, provided a suitable adapter is used. Likewise, null |
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| 39 | terminated strings can be treated as containers of characters, if suitably |
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| 40 | adapted. |
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| 41 | </p> |
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| 42 | |
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| 43 | <p> |
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| 44 | This library therefore provides the means to adapt standard-like |
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| 45 | containers, |
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| 46 | null terminated strings, <code>std::pairs</code> of iterators, and raw |
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| 47 | arrays (and more), such that the same generic code can work with them all. |
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| 48 | The basic idea is to add another layer of indirection using <a |
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| 49 | href="../../mpl/doc/refmanual/metafunction.html">metafunctions</a> and |
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| 50 | free-standing functions so syntactic and/or semantic differences can be removed. |
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| 51 | </p> |
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| 52 | |
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| 53 | <p > |
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| 54 | The main advantages are |
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| 55 | <ul > |
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| 56 | <li > |
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| 57 | simpler implementation and specification of generic range algorithms |
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| 58 | </li> |
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| 59 | <li > |
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| 60 | more flexible, compact and maintainable client code |
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| 61 | </li> |
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| 62 | <li > |
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| 63 | correct handling of null-terminated strings |
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| 64 | <p> |
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| 65 | <b>Warning:</b><i> support for null-terminated strings is deprecated and will |
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| 66 | disappear in the next Boost release (1.34). </i> |
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| 67 | </p> |
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| 68 | </li> |
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| 69 | <li > |
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| 70 | safe use of built-in arrays (for legacy code; why else would you use |
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| 71 | built-in arrays?) </li> |
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| 72 | |
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| 73 | </ul> |
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| 74 | </p> |
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| 75 | <p > |
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| 76 | Below are given a small example (the complete example can be found <a href="../test/algorithm_example.cpp" target="_self" >here</a> |
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| 77 | ): |
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| 78 | <blockquote> |
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| 79 | <pre > |
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| 80 | <span class=comment> |
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| 81 | // |
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| 82 | // example: extracting bounds in a generic algorithm |
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| 83 | // |
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| 84 | </span><span class=keyword>template</span><span class=special>< </span><span class=keyword>class </span><span class=identifier>ForwardReadableRange</span><span class=special>, </span><span class=keyword>class </span><span class=identifier>T </span><span class=special>> |
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| 85 | </span><span class=keyword>inline </span><span class=keyword>typename </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>range_iterator</span><span class=special>< </span><span class=identifier>ForwardReadableRange </span><span class=special>>::</span><span class=identifier>type |
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| 86 | </span><span class=identifier>find</span><span class=special>( </span><span class=identifier>ForwardReadableRange</span><span class=special>& </span><span class=identifier>c</span><span class=special>, </span><span class=keyword>const </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>value </span><span class=special>) |
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| 87 | </span><span class=special>{ |
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| 88 | </span><span class=keyword>return </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>find</span><span class=special>( </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>end</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>value </span><span class=special>); |
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| 89 | </span><span class=special>} |
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| 90 | |
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| 91 | </span><span class=keyword>template</span><span class=special>< </span><span class=keyword>class </span><span class=identifier>ForwardReadableRange</span><span class=special>, </span><span class=keyword>class </span><span class=identifier>T </span><span class=special>> |
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| 92 | </span><span class=keyword>inline </span><span class=keyword>typename </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>range_const_iterator</span><span class=special>< </span><span |
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| 93 | class=identifier>ForwardReadableRange </span><span class=special>>::</span><span class=identifier>type |
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| 94 | </span><span class=identifier>find</span><span class=special>( </span><span class=keyword>const </span><span class=identifier>ForwardReadableRange</span><span class=special>& </span><span class=identifier>c</span><span class=special>, </span><span class=keyword>const </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>value </span><span class=special>) |
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| 95 | </span><span class=special>{ |
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| 96 | </span><span class=keyword>return </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>find</span><span class=special>( </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>end</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>value </span><span class=special>); |
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| 97 | </span><span class=special>} |
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| 98 | |
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| 99 | </span><span class=comment>// |
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| 100 | // replace first value and return its index |
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| 101 | // |
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| 102 | </span><span class=keyword>template</span><span class=special>< </span><span class=keyword>class </span><span class=identifier>ForwardReadableWriteableRange</span><span class=special>, </span><span class=keyword>class </span><span class=identifier>T </span><span class=special>> |
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| 103 | </span><span class=keyword>inline </span><span class=keyword>typename </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>range_size</span><span class=special>< </span><span class=identifier>ForwardReadableWriteableRange </span><span class=special>>::</span><span class=identifier>type |
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| 104 | </span><span class=identifier>my_generic_replace</span><span class=special>( </span><span class=identifier>ForwardReadableWriteableRange</span><span class=special>& </span><span class=identifier>c</span><span class=special>, </span><span class=keyword>const </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>value</span><span class=special>, </span><span class=keyword>const </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>replacement </span><span class=special>) |
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| 105 | </span><span class=special>{ |
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| 106 | </span><span class=keyword>typename </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>range_iterator</span><span class=special>< </span><span class=identifier>ForwardReadableWriteableRange </span><span class=special>>::</span><span class=identifier>type </span><span class=identifier>found </span><span class=special>= </span><span class=identifier>find</span><span class=special>( </span><span class=identifier>c</span><span class=special>, </span><span class=identifier>value </span><span class=special>); |
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| 107 | |
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| 108 | </span><span class=keyword>if</span><span class=special>( </span><span class=identifier>found </span><span class=special>!= </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>end</span><span class=special>( </span><span class=identifier>c </span><span class=special>) </span><span class=special>) |
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| 109 | </span><span class=special>*</span><span class=identifier>found </span><span class=special>= </span><span class=identifier>replacement</span><span class=special>; |
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| 110 | </span><span class=keyword>return </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>distance</span><span class=special>( </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>found </span><span class=special>); |
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| 111 | </span><span class=special>} |
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| 112 | |
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| 113 | </span><span class=comment>// |
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| 114 | // usage |
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| 115 | // |
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| 116 | </span><span class=keyword>const </span><span class=keyword>int </span><span class=identifier>N </span><span class=special>= </span><span class=number>5</span><span class=special>; |
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| 117 | </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>vector</span><span class=special><</span><span class=keyword>int</span><span class=special>> </span><span class=identifier>my_vector</span><span class=special>; |
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| 118 | </span><span class=keyword>int </span><span class=identifier>values</span><span class=special>[] </span><span class=special>= </span><span class=special>{ </span><span class=number>1</span><span class=special>,</span><span class=number>2</span><span class=special>,</span><span class=number>3</span><span class=special>,</span><span class=number>4</span><span class=special>,</span><span class=number>5</span><span class=special>,</span><span class=number>6</span><span class=special>,</span><span class=number>7</span><span class=special>,</span><span class=number>8</span><span class=special>,</span><span class=number>9 </span><span class=special>}; |
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| 119 | </span> |
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| 120 | <span class=identifier>my_vector</span><span class=special>.</span><span |
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| 121 | class=identifier>assign</span><span class=special>( </span><span class=identifier>values</span><span class=special>, </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>end</span><span class=special>( </span><span class=identifier>values </span><span class=special>) </span><span class=special>);</span> |
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| 122 | </span><span class=keyword>typedef </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>vector</span><span class=special><</span><span class=keyword>int</span><span class=special>>::</span><span class=identifier>iterator </span><span class=identifier>iterator</span><span class=special>; |
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| 123 | </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>pair</span><span class=special><</span><span class=identifier>iterator</span><span class=special>,</span><span class=identifier>iterator</span><span class=special>> </span><span class=identifier>my_view</span><span class=special>( </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>my_vector </span><span class=special>), |
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| 124 | </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>my_vector </span><span class=special>) </span><span class=special>+ </span><span class=identifier>N </span><span class=special>); |
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| 125 | </span><span class=keyword>char </span><span class=identifier>str_val</span><span class=special>[] </span><span class=special>= </span><span class=string>"a string"</span><span class=special>; |
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| 126 | </span><span class=keyword>char</span><span class=special>* </span><span class=identifier>str </span><span class=special>= </span><span class=identifier>str_val</span><span class=special>; |
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| 127 | |
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| 128 | </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>cout </span><span class=special><< </span><span class=identifier>my_generic_replace</span><span class=special>( </span><span class=identifier>my_vector</span><span class=special>, </span><span class=number>4</span><span class=special>, </span><span class=number>2 </span><span class=special>); |
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| 129 | </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>cout </span><span class=special><< </span><span class=identifier>my_generic_replace</span><span class=special>( </span><span class=identifier>my_view</span><span class=special>, </span><span class=number>4</span><span class=special>, </span><span class=number>2 </span><span class=special>); |
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| 130 | </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>cout </span><span class=special><< </span><span class=identifier>my_generic_replace</span><span class=special>( </span><span class=identifier>str</span><span class=special>, </span><span class=literal>'a'</span><span class=special>, </span><span class=literal>'b' </span><span class=special>); |
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| 131 | </span> |
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| 132 | <span class=comment>// prints '3', '5' and '0' </span> |
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| 133 | </pre> |
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| 134 | </blockquote> |
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| 135 | |
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| 136 | By using the free-standing functions and <a |
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| 137 | href="../../mpl/doc/refmanual/metafunction.html">metafunctions</a>, the code automatically |
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| 138 | works for all the types supported by this library; now and in the future. |
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| 139 | Notice that we have to |
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| 140 | provide two version of <code >find()</code> since we cannot forward a non-const |
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| 141 | rvalue with reference arguments (see this article about <a href="http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_self" >The |
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| 142 | Forwarding Problem</a> ). |
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| 143 | |
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| 144 | </p> |
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| 145 | |
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| 146 | |
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| 147 | <hr> |
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| 148 | <p> |
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| 149 | (C) Copyright Thorsten Ottosen 2003-2004. Use, modification and distribution is subject to the Boost Software License, Version 1.0. |
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| 150 | </p> |
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| 151 | |
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| 152 | <br> |
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| 153 | <br> |
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| 154 | <br> |
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| 155 | <br> |
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| 156 | <br> |
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| 157 | <br> |
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| 158 | <br> |
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| 159 | <br> |
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| 160 | <br> |
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| 161 | <br> |
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| 162 | <br> |
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| 163 | <br> |
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| 164 | |
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| 165 | |
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| 166 | </body> |
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| 167 | </html> |
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| 168 | |
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