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从www.CppReference.com打包的C++参考手册

    count_if
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;algorithm&gt;
  size_t count_if( iterator start, iterator end, UnaryPred p );
</pre>

  <p>The count_if() function returns the number of elements between
  <em>start</em> and <em>end</em> for which the predicate <em>p</em>
  returns true.</p>

  <p>For example, the following code uses count_if() with a predicate
  that returns true for the integer 3 to count the number of items in
  an array that are equal to 3:</p>
  <pre class="example-code">
 int nums[] = { 0, 1, 2, 3, 4, 5, 9, 3, 13 };
 int start = 0;
 int end = 9;           

 int target_value = 3;
 int num_items = count_if( nums+start,
                    nums+end,
                    bind2nd(equal_to&lt;int&gt;(), target_value) );             

 cout &lt;&lt; &quot;nums[] contains &quot; &lt;&lt; num_items &lt;&lt; &quot; items matching &quot; &lt;&lt; target_value &lt;&lt; endl;               
</pre>

  <p>When run, the above code displays the following output:</p>
  <pre class="example-code">
 nums[] contains 2 items matching 3             
</pre>

  <div class="related-name-format">
    Related topics:
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  <div class="related-content">
    <a href="count.html">count</a>
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<hr>

  <div class="name-format">
    equal
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;algorithm&gt;
  bool equal( iterator start1, iterator end1, iterator start2 );
  bool equal( iterator start1, iterator end1, iterator start2, BinPred p );
</pre>

  <p>The equal() function returns true if the elements in two ranges
  are the same. The first range of elements are those between
  <em>start1</em> and <em>end1</em>. The second range of elements has
  the same size as the first range but starts at <em>start2</em>.</p>

  <p>If the binary predicate <em>p</em> is specified, then it is used
  instead of == to compare each pair of elements.</p>

  <p>For example, the following code uses equal() to compare two
  vectors of integers:</p>
  <pre class="example-code">
 vector&lt;int&gt; v1;
 for( int i = 0; i &lt; 10; i++ ) {
   v1.push_back( i );
 }              

 vector&lt;int&gt; v2;
 for( int i = 0; i &lt; 10; i++ ) {
   v2.push_back( i );
 }              

 if( equal( v1.begin(), v1.end(), v2.begin() ) ) {
   cout &lt;&lt; &quot;v1 and v2 are equal&quot; &lt;&lt; endl;
 } else {
   cout &lt;&lt; &quot;v1 and v2 are NOT equal&quot; &lt;&lt; endl;
 }              
</pre>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="find_if.html">find_if</a><br>
    <a href=
    "lexicographical_compare.html">lexicographical_compare</a><br>
    <a href="mismatch.html">mismatch</a><br>
    <a href="search.html">search</a>
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<hr>

  <div class="name-format">
    equal_range
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;algorithm&gt;
  pair&lt;iterator,iterator&gt; equal_range( iterator first, iterator last, const <a href="../containers.html">TYPE</a>&amp; val );
  pair&lt;iterator,iterator&gt; equal_range( iterator first, iterator last, const <a href="../containers.html">TYPE</a>&amp; val, CompFn comp );
</pre>

  <p>The equal_range() function returns the range of elements between
  <em>first</em> and <em>last</em> that are equal to <em>val</em>. This
  function assumes that the elements between <em>first</em> and
  <em>last</em> are in order according to <em>comp</em>, if it is
  specified, or the &lt; operator otherwise.</p>

  <p>equal_range() can be thought of as a combination of the <a href=
  "lower_bound.html">lower_bound</a>() and `upper_bound1`() functions,
  since the first of the pair of iterators that it returns is what
  <a href="lower_bound.html">lower_bound</a>() returns and the second
  iterator in the pair is what `upper_bound1`() returns.</p>

  <p>For example, the following code uses equal_range() to determine
  all of the possible places that the number 8 can be inserted into an
  ordered vector of integers such that the existing ordering is
  preserved:</p>
  <pre class="example-code">
 vector&lt;int&gt; nums;
 nums.push_back( -242 );
 nums.push_back( -1 );
 nums.push_back( 0 );
 nums.push_back( 5 );
 nums.push_back( 8 );
 nums.push_back( 8 );
 nums.push_back( 11 );          

 pair&lt;vector&lt;int&gt;::iterator, vector&lt;int&gt;::iterator&gt; result;
 int new_val = 8;               

 result = equal_range( nums.begin(), nums.end(), new_val );             

 cout &lt;&lt; &quot;The first place that &quot; &lt;&lt; new_val &lt;&lt; &quot; could be inserted is before &quot;
      &lt;&lt; *result.first &lt;&lt; &quot;, and the last place that it could be inserted is before &quot;
      &lt;&lt; *result.second &lt;&lt; endl;            
</pre>

  <p>The above code produces the following output:</p>
  <pre class="example-code">
 The first place that 8 could be inserted is before 8,
 and the last place that it could be inserted is before 11              
</pre>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="binary_search.html">binary_search</a><br>
    <a href="lower_bound.html">lower_bound</a><br>
    <a href="upper_bound.html">upper_bound</a>
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<hr>

  <div class="name-format">
    fill
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;algorithm&gt;
  #include &lt;algorithm&gt;
  void fill( iterator start, iterator end, const <a href=
"../containers.html">TYPE</a>&amp; val );
</pre>

  <p>The function fill() assigns <em>val</em> to all of the elements
  between <em>start</em> and <em>end</em>.</p>

  <p>For example, the following code uses fill() to set all of the
  elements of a vector of integers to -1:</p>
  <pre class="example-code">
 vector&lt;int&gt; v1;
 for( int i = 0; i &lt; 10; i++ ) {
   v1.push_back( i );
 }              

 cout &lt;&lt; &quot;Before, v1 is: &quot;;
 for( unsigned int i = 0; i &lt; v1.size(); i++ ) {
   cout &lt;&lt; v1[i] &lt;&lt; &quot; &quot;;
 }
 cout &lt;&lt; endl;            

 fill( v1.begin(), v1.end(), -1 );              

 cout &lt;&lt; &quot;After, v1 is: &quot;;
 for( unsigned int i = 0; i &lt; v1.size(); i++ ) {
   cout &lt;&lt; v1[i] &lt;&lt; &quot; &quot;;
 }
 cout &lt;&lt; endl;            
</pre>

  <p>When run, the above code displays:</p>
  <pre class="example-code">
 Before, v1 is: 0 1 2 3 4 5 6 7 8 9
 After, v1 is: -1 -1 -1 -1 -1 -1 -1 -1 -1 -1            
</pre>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="fill_n.html">fill_n</a><br>
    <a href="generate.html">generate</a><br>
    <a href="transform.html">transform</a>
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<hr>

  <div class="name-format">
    fill_n
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;algorithm&gt;
  #include &lt;algorithm&gt;
  iterator fill_n( iterator start, size_t n, const <a href=
"../containers.html">TYPE</a>&amp; val );
</pre>

  <p>The fill_n() function is similar to (C++ I/O) <a href=
  "../cppio/fill.html">fill</a>(). Instead of assigning <em>val</em> to
  a range of elements, however, fill_n() assigns <em>val</em> to the
  first <em>n</em> elements starting at <em>start</em>.</p>

  <p>For example, the following code uses fill_n() to assign -1 to the
  first half of a vector of integers:</p>
  <pre class="example-code">
 vector&lt;int&gt; v1;
 for( int i = 0; i &lt; 10; i++ ) {
   v1.push_back( i );
 }              

 cout &lt;&lt; &quot;Before, v1 is: &quot;;
 for( unsigned int i = 0; i &lt; v1.size(); i++ ) {
   cout &lt;&lt; v1[i] &lt;&lt; &quot; &quot;;
 }
 cout &lt;&lt; endl;            

 fill_n( v1.begin(), v1.size()/2, -1 );         

 cout &lt;&lt; &quot;After, v1 is: &quot;;
 for( unsigned int i = 0; i &lt; v1.size(); i++ ) {
   cout &lt;&lt; v1[i] &lt;&lt; &quot; &quot;;
 }
 cout &lt;&lt; endl;            
</pre>

  <p>When run, this code displays:</p>
  <pre class="example-code">
 Before, v1 is: 0 1 2 3 4 5 6 7 8 9
 After, v1 is: -1 -1 -1 -1 -1 5 6 7 8 9         
</pre>

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    Related topics:
  </div>

  <div class="related-content">
    <a href="fill.html">fill</a>
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<hr>

  <div class="name-format">
    find
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;algorithm&gt;
  iterator find( iterator start, iterator end, const <a href=
"../containers.html">TYPE</a>&amp; val );
</pre>

  <p>The find() algorithm looks for an element matching <em>val</em>
  between <em>start</em> and <em>end</em>. If an element matching
  <em>val</em> is found, the return value is an iterator that points to
  that element. Otherwise, the return value is an iterator that points
  to <em>end</em>.</p>

  <p>For example, the following code uses find() to search a vector of
  integers for the number 3:</p>
  <pre class="example-code">
 int num_to_find = 3;           

 vector&lt;int&gt; v1;
 for( int i = 0; i &lt; 10; i++ ) {
   v1.push_back(i);
 }              

 vector&lt;int&gt;::iterator result;
 result = find( v1.begin(), v1.end(), num_to_find );            

 if( result == v1.end() ) {
   cout &lt;&lt; &quot;Did not find any element matching &quot; &lt;&lt; num_to_find &lt;&lt; endl;
 }              

 else {
   cout &lt;&lt; &quot;Found a matching element: &quot; &lt;&lt; *result &lt;&lt; endl;
 }              
</pre>

  <p>In the next example, shown below, the find() function is used on
  an array of integers. This example shows how the C++ Algorithms can
  be used to manipulate arrays and pointers in the same manner that
  they manipulate containers and iterators:</p>
  <pre class="example-code">
 int nums[] = { 3, 1, 4, 1, 5, 9 };

 int num_to_find = 5;
 int start = 0;
 int end = 2;
 int* result = find( nums + start, nums + end, num_to_find );                

 if( result == nums + end ) {
   cout &lt;&lt; &quot;Did not find any number matching &quot; &lt;&lt; num_to_find &lt;&lt; endl;
 } else {
   cout &lt;&lt; &quot;Found a matching number: &quot; &lt;&lt; *result &lt;&lt; endl;
 }              
</pre>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="adjacent_find.html">adjacent_find</a><br>
    <a href="find_end.html">find_end</a><br>
    <a href="find_first_of.html">find_first_of</a><br>
    <a href="find_if.html">find_if</a><br>
    <a href="mismatch.html">mismatch</a><br>
    <a href="search.html">search</a>
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<hr>

  <div class="name-format">
    find_end
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;algorithm&gt;
  iterator find_end( iterator start, iterator end, iterator seq_start, iterator seq_end );
  iterator find_end( iterator start, iterator end, iterator seq_start, iterator seq_end, BinPred bp );
</pre>

  <p>The find_end() function searches for the sequence of elements
  denoted by <em>seq_start</em> and <em>seq_end</em>. If such a
  sequence if found between <em>start</em> and <em>end</em>, an
  iterator to the first element of the last found sequence is returned.
  If no such sequence is found, an iterator pointing to <em>end</em> is
  returned.</p>

  <p>If the binary predicate <em>bp</em> is specified, then it is used
  to when elements match.</p>

  <p>For example, the following code uses find_end() to search for two
  different sequences of numbers. The the first chunk of code, the last
  occurence of &quot;1 2 3&quot; is found. In the second chunk of code,
  the sequence that is being searched for is not found:</p>
  <pre class="example-code">
 int nums[] = { 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4 };
 int* result;
 int start = 0;
 int end = 11;          

 int target1[] = { 1, 2, 3 };
 result = find_end( nums + start, nums + end, target1 + 0, target1 + 2 );
 if( *result == nums[end] ) {
   cout &lt;&lt; &quot;Did not find any subsequence matching { 1, 2, 3 }&quot; &lt;&lt; endl;
 } else {
   cout &lt;&lt; &quot;The last matching subsequence is at: &quot; &lt;&lt; *result &lt;&lt; endl;
 }              

 int target2[] = { 3, 2, 3 };
 result = find_end( nums + start, nums + end, target2 + 0, target2 + 2 );
 if( *result == nums[end] ) {
   cout &lt;&lt; &quot;Did not find any subsequence matching { 3, 2, 3 }&quot; &lt;&lt; endl;
 } else {
   cout &lt;&lt; &quot;The last matching subsequence is at: &quot; &lt;&lt; *result &lt;&lt; endl;
 }              
</pre>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="adjacent_find.html">adjacent_find</a><br>
    <a href="find.html">find</a><br>
    <a href="find_first_of.html">find_first_of</a><br>
    <a href="find_if.html">find_if</a><br>
    <a href="search_n.html">search_n</a>
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<hr>

  <div class="name-format">
    find_first_of
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;algorithm&gt;
  iterator find_first_of( iterator start, iterator end, iterator find_start, iterator find_end );
  iterator find_first_of( iterator start, iterator end, iterator find_start, iterator find_end, BinPred bp );
</pre>

  <p>The find_first_of() function searches for the first occurence of
  any element between <em>find_start</em> and <em>find_end</em>. The
  data that are searched are those between <em>start</em> and
  <em>end</em>.</p>

  <p>If any element between <em>find_start</em> and <em>find_end</em>
  is found, an iterator pointing to that element is returned.
  Otherwise, an iterator pointing to <em>end</em> is returned.</p>

  <p>For example, the following code searches for a 9, 4, or 7 in an
  array of integers:</p>