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  25           <th width="60%" align="center">Chapter 12.
  26  Db_vector_base_iterator  </th>
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  36             <h2 class="title" style="clear: both"><a id="stldb_vector_base_iteratoroperator_sub"></a>operator-</h2>
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  44               <h3 class="title"><a id="stldb_vector_base_iteratoroperator_sub_details"></a>Function Details</h3>
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  48         <pre class="programlisting">
  49 self operator-(difference_type n) const
  50  </pre>
  51         <p>Iterator movement operator. </p>
  52         <p>Return another iterator by moving this iterator backward by n elements. </p>
  53         <div class="sect3" lang="en" xml:lang="en">
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  55             <div>
  56               <div>
  57                 <h4 class="title"><a id="idp765344"></a>Parameters</h4>
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  61           <div class="sect4" lang="en" xml:lang="en">
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  65                   <h5 class="title"><a id="idp767096"></a>n</h5>
  66                 </div>
  67               </div>
  68             </div>
  69             <p>The amount and direction of movement. If negative, will move backward by |n| element. </p>
  70           </div>
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  72         <div class="sect3" lang="en" xml:lang="en">
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  74             <div>
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  76                 <h4 class="title"><a id="idp764200"></a>Return Value</h4>
  77               </div>
  78             </div>
  79           </div>
  80           <p>The new iterator at new position. </p>
  81         </div>
  82         <pre class="programlisting">
  83 difference_type operator-(const self &amp;itr) const
  84  </pre>
  85         <p>Iterator distance operator. </p>
  86         <p>Return the index difference of this iterator and itr, so if this iterator sits on an element with a smaller index, this call will return a negative number. </p>
  87         <div class="sect3" lang="en" xml:lang="en">
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  91                 <h4 class="title"><a id="idp769496"></a>Parameters</h4>
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  99                   <h5 class="title"><a id="idp769688"></a>itr</h5>
 100                 </div>
 101               </div>
 102             </div>
 103             <p>The other iterator to substract. itr can be the invalid iterator after last element or before first element, their index will be regarded as last element's index + 1 and -1 respectively. </p>
 104           </div>
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 110                 <h4 class="title"><a id="idp759008"></a>Return Value</h4>
 111               </div>
 112             </div>
 113           </div>
 114           <p>The index difference. </p>
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 117       <div class="sect2" lang="en" xml:lang="en">
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 121               <h3 class="title"><a id="idp738736"></a>Group: Iterator movement operators.</h3>
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 125         <p>When we talk about iterator movement, we think the container is a uni-directional range, represented by [begin, end), and this is true no matter we are using iterators or reverse iterators.</p>
 126         <p>When an iterator is moved closer to "begin", we say it is moved forward, otherwise we say it is moved backward. </p>
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