c++ - 将 remove_copy_if 与 ostream_iterator 一起使用时确定复制范围的结尾

Question

我正在尝试使用remove_copy_if直接复制iterable到stdout通过ostream_iterator。remove_copy_if保证return value是到输出范围的iterator末尾。通过找出输出迭代器的起点和返回迭代器之间的距离，此返回值在确定复制到目标的元素数量方面很有用。这在使用容器时是有意义的，但是如何使用相同的功能来确定复制到目标的元素数量（如果它是ostream_iterator.

以下示例对我可能想要实现的目标应该更有意义

#include<vector>
#include<iterator>
#include<algorithm>
#include<functional>
#include<iostream>
#include <time.h>
using namespace std;
int  main() {
    int rawdata[] = {1,2,3,4,5,6,7,8,9,10,11};
    vector<int> data(20);
    vector<int>::iterator curr = remove_copy_if(rawdata,rawdata + sizeof(rawdata)/sizeof(rawdata[0]),data.begin(),bind2nd(greater<int>(),10));
    wcout<<L"No of data copied = "<<curr - data.begin()<<endl;
    for(int i=0;i<10;i++) {
    int some_value = rand()%20 + 1;
    ostream_iterator<int> curr = remove_copy_if(data.begin(),data.end(),ostream_iterator<int>(cout),bind2nd(less<int>(),some_value));
    //if (curr - what???? > 0) 
        cout<<endl;
    }
    return 0;
    } 

Answer 1

我遇到了以下非线程安全的，不是那么优雅的解决方案来完成这项工作。

#include<vector>
#include<iterator>
#include<algorithm>
#include<functional>
#include<iostream>
#include <time.h>
#include <algorithm>
using namespace std;
template<class _Fn1>
class counter
    : public std::unary_function<typename _Fn1::argument_type, bool>
    {   
    public:
    explicit counter(const _Fn1& _Func)
        : _Functor(_Func)   {
        count = countTrue = countFalse = 0;

        }

    bool operator()(const typename _Fn1::argument_type& _Left) const
        {   
        count++;
        if (_Functor(_Left)) {
        countTrue++;
        return true;
        } else {
            countFalse++;
            return false;
        }
        }
    static int count, countTrue,countFalse;
    protected:

    _Fn1 _Functor;  // the functor to apply
    };
template<class _Fn1>
int counter<_Fn1>::count=0,counter<_Fn1>::countTrue=0,counter<_Fn1>::countFalse=0;
int  main() {
    int rawdata[] = {1,2,3,4,5,6,7,8,9,10,11};
    vector<int> data(20);
    vector<int>::iterator curr = remove_copy_if(rawdata,rawdata + sizeof(rawdata)/sizeof(rawdata[0]),data.begin(),bind2nd(greater<int>(),10));
    wcout<<L"No of data copied = "<<curr - data.begin()<<endl;
    for(int i=0;i<10;i++) {
    int some_value = rand()%20 + 1;
    ostream_iterator<int> curr = remove_copy_if(data.begin(),data.end(),ostream_iterator<int>(cout),counter<binder2nd<less<int>>>(bind2nd(less<int>(),some_value)));
    if (counter<binder2nd<less<int>>>::countFalse) {
    cout<<endl<<"No of data printed = "<<counter<binder2nd<less<int>>>::countFalse<<endl;
    }
    }
    return 0;
    }