【发布时间】：2015-09-01 20:02:10
【问题描述】：
我想维护一个堆，其中有效负载为MoveConstructible（因为它们在内部包含std::unique_ptr。）尽管documentation 建议对象必须是MoveAssignable 和MoveConstructible，但这样做会引发GCC 和 Clang 中的错误。
示例代码
我还没有使用std::unique_ptr，只是禁用了相应的复制操作符）：
#include <iostream>
#include <vector>
#include <algorithm>
struct Data {
explicit Data(int value) : value(value) {}
int value;
bool operator<(const Data& d) const {
return value > d.value;
}
/**
* Commenting out the rest of the section for this struct
* gets the code working by using copy operator/ctor.
*/
explicit Data(const Data& d) = delete;
Data& operator=(const Data& d) = delete;
explicit Data(Data&& d) = default;
Data& operator=(Data&& d) = default;
};
struct MinHeap {
void Push(Data&& d) {
container_.emplace_back(std::move(d));
std::push_heap(container_.begin(), container_.end());
}
Data Pop() {
std::pop_heap(container_.begin(), container_.end());
Data d = std::move(container_.back());
container_.pop_back();
return std::move(d);
}
size_t size() const { return container_.size(); }
bool empty() const { return size() == 0; }
private:
std::vector<Data> container_;
};
int main() {
MinHeap h;
h.Push(Data(5));
h.Push(Data(8));
h.Push(Data(11));
h.Push(Data(3));
h.Push(Data(7));
while (!h.empty()) {
Data d = std::move(h.Pop());
std::cout << d.value << std::endl;
}
return 0;
}
知道我做错了什么，以及如何让堆使用移动语义？
错误
In file included from /usr/include/c++/4.9.2/bits/stl_pair.h:59:0,
from /usr/include/c++/4.9.2/bits/stl_algobase.h:64,
from /usr/include/c++/4.9.2/bits/char_traits.h:39,
from /usr/include/c++/4.9.2/ios:40,
from /usr/include/c++/4.9.2/ostream:38,
from /usr/include/c++/4.9.2/iostream:39,
from main.cpp:1:
/usr/include/c++/4.9.2/bits/stl_heap.h: In instantiation of 'void std::push_heap(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__norma
l_iterator<Data*, std::vector<Data> >]':
main.cpp:25:56: required from here
/usr/include/c++/4.9.2/bits/stl_heap.h:164:28: error: no matching function for call to 'Data::Data(std::remove_reference<Data&>::type
)'
_ValueType __value = _GLIBCXX_MOVE(*(__last - 1));
^
In file included from /usr/include/c++/4.9.2/bits/stl_algo.h:61:0,
from /usr/include/c++/4.9.2/algorithm:62,
from main.cpp:3:
/usr/include/c++/4.9.2/bits/stl_heap.h:167:45: error: no matching function for call to 'Data::Data(std::remove_reference<Data&>::type
)'
__gnu_cxx::__ops::__iter_less_val());
^
/usr/include/c++/4.9.2/bits/stl_heap.h:124:5: error: initializing argument 4 of 'void std::__push_heap(_RandomAccessIterator, _Dist
ance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Data*, std::vector<Data> >; _Distance = lo
ng int; _Tp = Data; _Compare = __gnu_cxx::__ops::_Iter_less_val]'
__push_heap(_RandomAccessIterator __first,
^
In file included from /usr/include/c++/4.9.2/bits/stl_pair.h:59:0,
from /usr/include/c++/4.9.2/bits/stl_algobase.h:64,
from /usr/include/c++/4.9.2/bits/char_traits.h:39,
from /usr/include/c++/4.9.2/ios:40,
from /usr/include/c++/4.9.2/ostream:38,
from /usr/include/c++/4.9.2/iostream:39,
from main.cpp:1:
/usr/include/c++/4.9.2/bits/stl_heap.h: In instantiation of 'void std::__pop_heap(_RandomAccessIterator, _RandomAccessIterator, _Rand
omAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Data*, std::vector<Data> >; _Compare = __gnu_c
xx::__ops::_Iter_less_iter]':
/usr/include/c++/4.9.2/bits/stl_heap.h:280:42: required from 'void std::pop_heap(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__nor
mal_iterator<Data*, std::vector<Data> >]'
main.cpp:29:55: required from here
/usr/include/c++/4.9.2/bits/stl_heap.h:243:28: error: no matching function for call to 'Data::Data(std::remove_reference<Data&>::type
)'
_ValueType __value = _GLIBCXX_MOVE(*__result);
^
In file included from /usr/include/c++/4.9.2/bits/stl_algo.h:61:0,
from /usr/include/c++/4.9.2/algorithm:62,
from main.cpp:3:
/usr/include/c++/4.9.2/bits/stl_heap.h:247:35: error: no matching function for call to 'Data::Data(std::remove_reference<Data&>::type
)'
_GLIBCXX_MOVE(__value), __comp);
^
/usr/include/c++/4.9.2/bits/stl_heap.h:207:5: error: initializing argument 4 of 'void std::__adjust_heap(_RandomAccessIterator, _Di
stance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Data*, std::vector<Data> >; _Distance =
long int; _Tp = Data; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
__adjust_heap(_RandomAccessIterator __first, _Distance __holeIndex,
^
【问题讨论】：
-
具有
explicit移动构造函数的类型不满足MoveConstructible。 -
谢谢。是的，这解决了问题。
-
虽然我看到您最初的问题已解决，但您应该注意一些事情。 push_heap 的要求只有 MoveConstructible/Assignable，是的。但是你也在向量上做一个 emplace_back 。 vector 有一个更复杂的要求：您要么需要一个 noexcept 移动构造函数/移动赋值，要么需要一个复制构造函数。您的示例有效，因为默认生成的移动功能没有例外（在这种情况下）；如果您自己编写，则需要显式使用 noexcept（请注意，unique_ptr 满足此要求）。
-
谢谢@NirFriedman。我知道这个问题，但感谢您指出。
标签： c++ c++11 stl heap move-semantics