扁平化容器容器的通用函数 [英] Generic function to flatten a container of containers

问题描述

我试图更好地掌握迭代器和泛型函数.我认为编写一个转换 container1 < 的函数将是一个有用的练习.容器2<类型>> 到 container3 <type>.例如，它应该能够转换 vector<;双端队列<int>> 到 list<int>.

I am trying to get a better hold on iterators and generic functions. I thought it would be a useful exercise to write a function that converts container1 < container2 <type> > to container3 <type>. For example, it should be able to convert vector< deque<int> > to list<int>.

我认为所有容器访问都应该通过迭代器，就像 <algorithm> 中的函数一样.

I figured all the container access should be through iterators, like the functions in <algorithm>.

这是我的代码:

#include <iterator>
#include <algorithm>

// COCiter == Container of Containers Iterator
// Oiter == Output Iterator
template <class COCiter, class Oiter>
void flatten (COCiter start, COCiter end, Oiter dest)
{
    using namespace std;

    while (start != end) {
        dest = copy(start->begin(), start()->end(), dest);
        ++start;
    }
}

但是当我尝试在下面的代码中调用它时:

But when I try to call it in the following code:

int main ()
{
    using namespace std;

    vector< vector<string> > splitlines;
    vector<string> flat;

    /* some code to fill SPLITLINES with vectors of strings */

    flatten(splitlines.begin(), splitlines.end(), back_inserter(flat));
}

我收到一条巨大的 C++ 模板错误消息，undefined reference to void flatten<...模板页面...

I get a huge C++ template error message, undefined reference to void flatten< ... pages of templates ...

我觉得我的代码写得太容易了，我必须需要更多的东西来确保内部容器中的数据类型与输出容器中的数据类型匹配.但我不知道该怎么办.

I feel like my code was too easy to write, and I must need some more stuff to ensure that the data type in the inner containers matches the data type in the output container. But I don't know what to do.

推荐答案

我发现了问题.感谢 SFINAE(替换失败不是错误)，您的编译器找不到正确的模板，因为您试图通过键入 在 start 上调用 operator()start() (可能是错字).试试这个:

I found the issue. Thanks to SFINAE (Substitution failure is not an error) your compiler couldn't find the correct template because you are trying to call operator() on start by typing start() (probably a typo). Try this:

#include <iterator>
#include <algorithm>

// COCiter == Container of Containers Iterator
// Oiter == Output Iterator
template <class COCiter, class Oiter>
void flatten (COCiter start, COCiter end, Oiter dest) {
    while (start != end) {
        dest = std::copy(start->begin(), start->end(), dest);
        ++start;
    }
}

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