Boolan STL与泛型编程 第四周作业

编写一个Sink迭代器，同时可以完成inserter迭代器和打印数值的功能

本周的作业如上面所示了。要求是编写一个迭代器，将默认的inserter迭代器的功能实现，并且在每次迭代的时候能够把容器内的数据打印出来。
既然如此，那我们就把inserter改一改吧。

//sink.h
#include <iostream>
#include <iterator>
template <class Container>
class sink_iterator {
public:
    typedef std::output_iterator_tag iterator_category;
    typedef typename Container::value_type value_type;
    typedef typename Container::difference_type difference_type;
    typedef typename Container::pointer pointer;
    typedef typename Container::reference reference;

protected:
    Container* container;
    typename Container::iterator iter;

public:
    sink_iterator(Container &x, typename Container::iterator i):container(&x), iter(i) {};

    sink_iterator<Container>& operator= (const typename Container::value_type& value) {
        iter = container->insert(iter, value);
        ++iter;
        std::cout << value << " ";
        return *this;
    }

};

这样就把inserter的迭代器给写好了，不过还差一个辅助函数用来调用sink_iterator。那就是sink本函。

template <class Container, class Iterator>
inline sink_iterator<Container> sink(Container& x, Iterator i) {
    typedef typename Container::iterator iter;
    return sink_iterator<Container>(x, iter(i));
};

这样做好之后，我用如下的测试代码进行测试。

//main.cpp
#include <iostream>
#include <vector>
#include <list>
#include "sink.h"

int main() {
    int myints[] = {10,20,30,40,50,60,70};
    std::vector<int> myvec(7);

    std::copy(myints, myints+7, myvec.begin());
    for(auto& i: myvec)
        std::cout << i << " ";

    std::cout << std::endl;

    std::list<int> foo, bar;
    for(int i=1;i<=5;i++) {
        foo.push_back(i); bar.push_back(i*10);
    }

    auto it = foo.begin();
    std::advance(it, 3);

    std::copy(bar.begin(),bar.end(),sink(foo,it));
    return 0;
}

编译的时候，却提示我。

C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/7.3.0/include/c++/bits/stl_algobase.h:293:30: error: no match for 'operator++' (operand type is 'sink_iterator<std::__cxx11::list<int> >')
    for (; __first != __last; ++__result, (void)++__first)
                              ^~~~~~~~~~
C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/7.3.0/include/c++/bits/stl_algobase.h:294:6: error: no match for 'operator*' (operand type is 'sink_iterator<std::__cxx11::list<int> >')
      *__result = *__first;
      ^~~~~~~~~

看来想偷懒只写出operator=是不行的。还需要对operator++和operator*操作符进行实现。

#include <iostream>
#include <iterator>

template <class Container>
class sink_iterator {
public:
    typedef std::output_iterator_tag iterator_category;
    typedef typename Container::value_type value_type;
    typedef typename Container::difference_type difference_type;
    typedef typename Container::pointer pointer;
    typedef typename Container::reference reference;

protected:
    Container* container;
    typename Container::iterator iter;

public:
    sink_iterator(Container &x, typename Container::iterator i):container(&x), iter(i) {};

    sink_iterator<Container>& operator= (const typename Container::value_type& value) {
        iter = container->insert(iter, value);
        ++iter;
        std::cout << value << " ";
        return *this;
    }

    sink_iterator<Container>& operator++ () {
        ++iter;
        return *this;
    }

    sink_iterator<Container>& operator*() {
        return *this;
    }

};


template <class Container, class Iterator>
inline sink_iterator<Container> sink(Container& x, Iterator i) {
    typedef typename Container::iterator iter;
    return sink_iterator<Container>(x, iter(i));
};

然后再进行编译就调试通过了。
程序运行结果是：

10 20 30 40 50 60 70
10 20 30 40 50

与预期结果完全一致。