STL Sample for the count_if FunctionLast reviewed: October 9, 1997Article ID: Q156300 |
The information in this article applies to:
SUMMARYThe sample code below illustrates how to use the count_if, begin, and end STL function in Visual C++.
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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.
DescriptionThe 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> // 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
REFERENCESVisual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.
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Additional query words: STL count_if begin end
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