什么是同时迭代两个或更多容器的最好方法 [英] What's the best way to iterate over two or more containers simultaneously

问题描述

C ++ 11提供了多种方法来遍历容器。例如：

C++11 provides multiple ways to iterate over containers. For example:

for(auto c : container) fun(c)

std :: for_each

std::for_each

for_each(container.begin(),container.end(),fun)

但是，建议使用同样大小的两个（或更多）容器来完成类似的操作：

However what is the recommended way to iterate over two (or more) containers of the same size to accomplish something like:

for(unsigned i = 0; i < containerA.size(); ++i) {
  containerA[i] = containerB[i];
}

推荐答案

使用

std::copy_n(contB.begin(), contA.size(), contA.begin())

对于更一般的情况，可以使用Boost.Iterator的 zip_iterator ，有一个小功能，使其可用于基于范围的for循环。在大多数情况下，这将工作：

For the more general case, you can use Boost.Iterator's zip_iterator, with a small function to make it usable in range-based for loops. For most cases, this will work:

template<class... Conts>
auto zip_range(Conts&... conts)
  -> decltype(boost::make_iterator_range(
  boost::make_zip_iterator(boost::make_tuple(conts.begin()...)),
  boost::make_zip_iterator(boost::make_tuple(conts.end()...))))
{
  return {boost::make_zip_iterator(boost::make_tuple(conts.begin()...)),
          boost::make_zip_iterator(boost::make_tuple(conts.end()...))};
}

// ...
for(auto&& t : zip_range(contA, contB))
  std::cout << t.get<0>() << " : " << t.get<1>() << "\n";

Live example。

但是，对于完整的一般性，你可能想要更像 this ，对于没有成员 begin（） / end（）的数组和用户定义类型， 但 do 在其命名空间中有 begin / 。此外，这将允许用户通过 zip_c ... 函数专门获取 const 。

However, for full-blown genericity, you probably want something more like this, which will work correctly for arrays and user-defined types that don't have member begin()/end() but do have begin/end functions in their namespace. Also, this will allow the user to specifically get const access through the zip_c... functions.

如果你是一个好主意的错误信息，像我一样，那么你可能想要这个，它检查是否有任何临时容器传递给任何 zip _... 函数，并打印一个不错的错误消息。

And if you're an advocate of nice error messages, like me, then you probably want this, which checks if any temporary containers were passed to any of the zip_... functions, and prints a nice error message if so.

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