Q156300: STL Sample for the count_if Function

Article: Q156300
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): _IK
Last Modified: 07-MAY-2001

-------------------------------------------------------------------------------
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 
-------------------------------------------------------------------------------

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

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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.