迭代器适配器仅迭代地图中的值?-C/C++问题

iterator adapter to iterate just the values in a map?(迭代器适配器仅迭代地图中的值?)

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问题描述

在做了几年 C# 和最近的 Objective C 之后，我才刚刚回到 C++.

I'm just getting back into C++ after a couple of years of doing a lot of C#, and recently Objective C.

我之前做过的一件事是为 std::map 滚动我自己的迭代器适配器，它将只引用值部分，而不是键值对.这是很常见和很自然的事情.C# 为这个工具提供了它的 Dictionary 类的 Keys 和 Values 属性.Objective-C 的 NSDictionary 同样具有 allKeys 和 allValues.

One thing I've done before is to roll my own iterator adapter for std::map that will deref to just the value part, rather than the key-value pair. This is quite a common and natural thing to do. C# provides this facility with its Keys and Values properties of its Dictionary class. Objective-C's NSDictionary, similarly, has allKeys and allValues.

自从我离开"以来，Boost 已经获得了 Range 和 ForEach 库，我现在正在广泛使用它们.我想知道两者之间是否有一些设施可以做同样的事情，但我找不到任何东西.

Since I've been "away", Boost has acquired the Range and ForEach libraries, which I am now using extensively. I wondered if between the two there was some facility to do the same, but I haven't been able to find anything.

我正在考虑使用 Boost 的迭代器适配器来解决问题，但在我走这条路之前，我想我想在这里问一下是否有人知道 Boost 中的这种设施，或者其他现成的地方?

I'm thinking of knocking something up using Boost's iterator adapters, but before I go down that route I thought I'd ask here if anyone knows of such a facility in Boost, or somewhere else ready made?

推荐答案

我不认为有什么开箱即用的.你可以使用 boost::make_transform.

I don't think there's anything out of the box. You can use boost::make_transform.

template<typename T1, typename T2> T2& take_second(const std::pair<T1, T2> &a_pair) 
{
  return a_pair.second;
}

void run_map_value()
{
  map<int,string> a_map;
  a_map[0] = "zero";
  a_map[1] = "one";
  a_map[2] = "two";
  copy( boost::make_transform_iterator(a_map.begin(), take_second<int, string>),
    boost::make_transform_iterator(a_map.end(), take_second<int, string>),
    ostream_iterator<string>(cout, "
")
    );
}

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