泛型算法系列9:count()&&count_if()

#include <iostream>#include <algorithm>#include <vector>#include <algorithm>#include <fstream>using namespace std; template<class _InIt, class _Ty> inlinetypename iterator_traits<_InIt>::difference_type_Count(_InIt _First, _InIt _Last, const _Ty& _Val){// count elements that match _Val_DEBUG_RANGE(_First, _Last);typename iterator_traits<_InIt>::difference_type _Cnt = 0;for (; _First != _Last; ++_First)if (*_First == _Val)++_Cnt;return (_Cnt);}/************************************************************************//* *//************************************************************************/int main(int argc, char* argv[]){ int a[]={1,1,2,3,4,5,4,4,5}; int elem_count = 0; elem_count=count( a,a+9,5 ); cout<< elem_count << " times/n";return 0;}

 

下面是count_if的例子

 

#include <iostream>#include <algorithm>#include <vector>#include <algorithm>#include <fstream>#include <list>using namespace std;class Even {public:bool operator()( int val ){ return val%2 ? false : true; }};int main(){int ia[] = {0,1,1,2,3,5,8,13,21,34};list< int> ilist( ia, ia+10 );/** unsupported in current implementation*****************************************************typedefiterator_traits<InputIterator>::distance_typedistance_type;distance_type ia_count, list_count;// count even elements: 4ia_count = count_if( &ia[0], &ia[10], Even() );list_count = count_if( ilist.begin(), ilist_end(),bind2nd(less<int>(),10) );*******************************************************/int ia_count =count_if( &ia[0], &ia[10], Even());// generates:// count_if(): there are 4 elements that are even.cout << "count_if(): there are "<< ia_count << " elements that are even./n";int list_count =count_if( ilist.begin(), ilist.end(),bind2nd(less<int>(),10));// generates:// count_if(): there are 7 elements that are less than 10.cout << "count_if(): there are "<< list_count<< " elements that are less than 10./n";return 0;}/************************************************************************//*template<class _InIt, class _Pr> inlinetypename iterator_traits<_InIt>::difference_type_Count_if(_InIt _First, _InIt _Last, _Pr _Pred){// count elements satisfying _Pred_DEBUG_RANGE(_First, _Last);_DEBUG_POINTER(_Pred);typename iterator_traits<_InIt>::difference_type _Count = 0;for (; _First != _Last; ++_First)if (_Pred(*_First))++_Count;return (_Count);}*//************************************************************************//************************************************************************//* */template<class _Fn2>class binder2nd: public unary_function<typename _Fn2::first_argument_type,typename _Fn2::result_type>{// functor adapter _Func(left, stored)public:typedef unary_function<typename _Fn2::first_argument_type,typename _Fn2::result_type> _Base;typedef typename _Base::argument_type argument_type;typedef typename _Base::result_type result_type;binder2nd(const _Fn2& _Func,const typename _Fn2::second_argument_type& _Right): op(_Func), value(_Right){// construct from functor and right operand}result_type operator()(const argument_type& _Left) const{// apply functor to operandsreturn (op(_Left, value));}result_type operator()(argument_type& _Left) const{// apply functor to operandsreturn (op(_Left, value));}protected:_Fn2 op;// the functor to applytypename _Fn2::second_argument_type value;// the right operand};/************************************************************************/