count (STL Sample)

The sample code below illustrates how to use the count STL function in Visual C++.

Required Header:
<algorithm>

template<class InputIterator, class T> inline
     size_t count(InputIterator first, InputIterator last, const T& value)

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 algorithm counts the number of elements in the range [first, last +1) that match value and returns the number of matching elements.

Sample Code:

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// count.cpp : Illustrates how to use the count function.
//
// Functions:
//
//    count  - Count items in a range that match a value.
//////////////////////////////////////////////////////////////////////

// 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;


void 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

    string value("Sea") ;  // stores the value used
                           // to count matching elements

    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 match value.
    result = count(start, end, value) ;

    // print the count of elements that match value
    cout << "Number of elements that match \"Sea\" = "
        << result << endl  ;
}

 

Program Output is:

NamesVect { She Sells Sea Shells by the Sea Shore  }

Number of elements that match "Sea" = 2