count_if
abs
TOC
Collapse the table of content
Expand the table of content
Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here. ArchiveDisclaimer

count_if (STL Samples) 

Illustrates how to use the count_if Standard Template Library (STL) function in Visual C++.


template<class InputIterator, class Predicate> inline 
   size_t count_if(
      InputIterator First,
      InputIterator Last,
      Predicate P
   )

NoteNote

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

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.

// countif.cpp
// compile with: /EHsc
//
// 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.

// 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) ;
}

int main()
{
    const int VECTOR_SIZE = 8 ;

    // Define a template class vector of strings
    typedef vector<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 ;

    ptrdiff_t 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  ;
}

NamesVect { She Sells Sea Shells by the Sea Shore  }

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

Header: <algorithm>

Show:
© 2016 Microsoft