DOCUMENT:Q156300  07-MAY-2001  [visualc]
TITLE   :STL Sample for the count_if Function
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:
OPER/SYS:
KEYWORDS:_IK

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-------------------------------------------------------------------------------
The information in this article applies to:

 - The Standard C++ Library, included with:
    - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 4.2 
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SUMMARY
=======

The sample code below illustrates how to use the count_if, begin, and end STL
function in Visual C++.

MORE INFORMATION
================

Required Header
---------------

   <algorithm>
    

Prototype
---------

      template<class InputIterator, class Predicate>  inline
          size_t count_if(InputIterator first, InputIterator last,
                                 Predicate P)

NOTE: The class/parameter names in the prototype do not match the version in the
header file. Some have been modified to improve readability.

Description
-----------

The count_if algorithm counts the number of elements in the range [first, last)
that cause the predicate to return true, and returns the number of elements for
which the predicate was true.

Sample Code
-----------

   ////////////////////////////////////////////////////////////////////// 
   // 
   // Compile options needed: /GX
   // 
   // count.cpp : Illustrates how to use the count_if function.
   // 
   // Functions:
   // 
   //   count_if  - Count items in a range that satisfy a predicate.
   // 
   //   begin     - Returns an iterator that points to the first element in
   //               a sequence.
   // 
   //   end       - Returns an iterator that points one past the end of a
   //               sequence.
   // 
   // Written by Kalindi Sanghrajka
   // of Microsoft Product Support Services,
   // Software Core Developer Support.
   // Copyright (c) 1996 Microsoft Corporation. All rights reserved.
   ////////////////////////////////////////////////////////////////////// 

   // disable warning C4786: symbol greater than 255 character,
   // okay to ignore
   #pragma warning(disable: 4786)

   #include <iostream>
   #include <algorithm>
   #include <functional>
   #include <string>
   #include <vector>
   using namespace std;

   // Return true if string str starts with letter 'S'
   int MatchFirstChar( const string& str)
   {
       string s("S") ;
       return s == str.substr(0,1) ;
   }

   void main()
   {
       const int VECTOR_SIZE = 8 ;

       // Define a template class vector of strings
       typedef vector<string, allocator<string> > StringVector ;

       //Define an iterator for template class vector of strings
       typedef StringVector::iterator StringVectorIt ;

       StringVector NamesVect(VECTOR_SIZE) ;   //vector containing names

       StringVectorIt start, end, it ;

       int result = 0 ;   // stores count of elements
                          // that match value.

       // Initialize vector NamesVect
       NamesVect[0] = "She" ;
       NamesVect[1] = "Sells" ;
       NamesVect[2] = "Sea" ;
       NamesVect[3] = "Shells" ;
       NamesVect[4] = "by" ;
       NamesVect[5] = "the" ;
       NamesVect[6] = "Sea" ;
       NamesVect[7] = "Shore" ;

       start = NamesVect.begin() ;   // location of first
                                     // element of NamesVect

       end = NamesVect.end() ;       // one past the location
                                     // last element of NamesVect

       // print content of NamesVect
       cout << "NamesVect { " ;
       for(it = start; it != end; it++)
           cout << *it << " " ;
       cout << " }\n" << endl ;

       // Count the number of elements in the range [first, last +1)
       // that start with letter 'S'
       result = count_if(start, end, MatchFirstChar) ;

       // print the count of elements that start with letter 'S'
       cout << "Number of elements that start with letter \"S\" = "
           << result << endl  ;
   }

Output:

NamesVect { She Sells Sea Shells by the Sea Shore }

Number of elements that start with letter "S" = 6

REFERENCES
==========

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

Additional query words: STL count_if begin end

======================================================================
Keywords          : _IK 
Technology        : kbVCsearch kbAudDeveloper kbVCLibrary
Version           : winnt:
Issue type        : kbhowto

=============================================================================

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