[英]Forward iterator with a moving end()
So, I'm designing a class which connects (over network) to a service to receive some data. 因此,我正在设计一个类(通过网络)连接到服务以接收一些数据的类。 I don't know how man data points I will be receiving in advance. 我不知道我将如何预先接收人工数据点。 Nevertheless I was wondering, if there is a way to make this class iterable using a forward_iterator in order to enjoy the STL in its full glory. 但是,我想知道,是否有一种方法可以使用forward_iterator使该类可迭代,以便充分享受STL的乐趣。 My idea was something like: 我的想法是这样的:
self_type operator++() {
// if there are some locally cached data points left return next
// else connect to service again to receive the next batch of data
}
However, as I cannot provide a valid end()
, I'm curious, if this is somehow still possible to do. 但是,由于我不能提供有效的end()
,我很好奇,如果仍然可以做到这一点。
An alternative (and iterator-less) interface would probably look something like: 一个替代的(且无迭代器的)接口可能类似于:
bool hasMoreDataPoints() const;
DataPoint& getNext();
which obviously won't work with any STL-algorithm. 这显然不适用于任何STL算法。
Do as the standard library do with istream_iterator
: when you run out of data, set your iterator state such that it compares equal to a default-constructed object of that type. 像使用istream_iterator
的标准库一样进行操作:当数据用尽时,请设置迭代器状态,使其与该类型的默认构造对象进行比较。 And then there's your end()
equivalent. 然后是您的end()
等效项。
I suppose there is some type of storage which you use in your class for caching, eg a std::vector
. 我想您可以在类中使用某种类型的存储来进行缓存,例如std::vector
。 You can then just expose its std::begin()
and std::end()
iterators (in all the usual forms). 然后,您可以仅公开其std::begin()
和std::end()
迭代器(以所有常用形式)。 Algorithms then directly work on the underlying container, and use the container-iterator's member functions like operator++
, operator==
and so on. 然后,算法直接在基础容器上工作,并使用容器迭代器的成员函数,例如operator++
, operator==
等。
In case you need to introduce more logic, you need to create your custom iterator. 如果需要引入更多逻辑,则需要创建自定义迭代器。 Such can be basically done by composition, ie write a new class which contains an iterator corresponding to your storage container, and expose all functionality you need while adjusting it accordingly. 这基本上可以通过组合来完成,即编写一个包含与您的存储容器相对应的迭代器的新类,并公开您所需的所有功能,同时进行相应的调整。
EDIT: as you said you use a list: 编辑:正如您所说的,您使用列表:
struct DataPoints
{
std::list<double> _list;
auto begin() const
{
return _list.begin();
}
auto end() const
{
return _list.end();
}
//other versions: non-const begin and end, cbegin, cend
}
That's it already for the simple approach. 简单的方法就已经足够了。 You can use that just as a normal list: 您可以将其用作普通列表:
DataPoints d;
std::find(d.begin(), d.end(), 10.0);
As said, if you need more logic, you probably need to write a custom iterator. 如前所述,如果您需要更多逻辑,则可能需要编写自定义迭代器。
However, as I cannot provide a valid end(), I'm curious, if this is somehow still possible .... 但是,由于我不能提供有效的end(),我很好奇,如果仍然可以做到这一点 ...。
You could use any of the container classes that comes with STL. 您可以使用STL随附的任何容器类。 Assume you are using a vector or a list or any other suitable container. 假设您正在使用向量或列表或任何其他合适的容器。 Just use what's provided by STL and write your own wrapper 只需使用STL提供的内容并编写自己的包装器
vector<datapoint> mydpvector;
//as data comes in
mydpvector.push_back(newdp);
vector<datapoint>::const_iterator cit=mydpvector.begin();
//now iterate everytime over the container
for(cit;cit!=mydpvector.end();cit++)
{
//get the data you need
}
//alternately if you need just the last element do this
mostrecentdp = mydpvector.back();
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