C++ std::back_inserter 用于 std::set？
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std::back_inserter for a std::set?
提问by rlbond
I guess this is a simple question. I need to do something like this:
我想这是一个简单的问题。我需要做这样的事情：
std::set<int> s1, s2;
s1 = getAnExcitingSet();
std::transform(s1.begin(), s1.end(), std::back_inserter(s2), ExcitingUnaryFunctor());
Of course, std::back_inserterdoesn't work since there's no push_back.
std::inserteralso needs an iterator? I haven't used std::inserterso I'm not sure what to do.
当然，std::back_inserter不起作用，因为没有push_back.
std::inserter还需要迭代器？我没用过std::inserter所以我不知道该怎么做。
Does anyone have an idea?
有没有人有想法？
当然，我的另一个选择是对 使用向量
s2s2，然后稍后对其进行排序。也许这样更好？回答by Johannes Schaub - litb
setdoesn't have push_backbecause the position of an element is determined by the comparator of the set. Use std::inserterand pass it .begin():
set没有，push_back因为元素的位置由集合的比较器决定。使用std::inserter并传递它.begin()：
std::set<int> s1, s2;
s1 = getAnExcitingSet();
transform(s1.begin(), s1.end(),
std::inserter(s2, s2.begin()), ExcitingUnaryFunctor());
The insert iterator will then call s2.insert(s2.begin(), x)where xis the value passed to the iterator when written to it. The set uses the iterator as a hint where to insert. You could as-well use s2.end().
然后插入迭代器将调用传递给迭代器的值s2.insert(s2.begin(), x)在哪里x写入。该集合使用迭代器作为插入位置的提示。你也可以使用s2.end().
回答by alfC
In 2016 there was a proposal to have a "single argument inserteriterator".
https://isocpp.org/files/papers/p0471r0.html. I couldn't find if it the proposal advanced. I think it makes sense.
2016 年，有人提议使用“单参数inserter迭代器”。
https://isocpp.org/files/papers/p0471r0.html。我找不到提案是否有进展。我认为这是有道理的。
For now you can have this behavior defining the maker function:
现在，您可以使用以下行为来定义 maker 函数：
template<class Container>
auto sinserter(Container& c){
using std::end;
return std::inserter(c, end(c));
}
Used as:
用作：
std::transform(begin(my_vec), end(my_vec), sinserter(my_set), [](auto& e){return e.member;});
