为什么我在这个 omp_declare_reduction 中得到这个错误？

Question

我有这个文件：

啊.h

struct B;

struct A
{
    A(... B &b) :
        b(b) {}

    B &b;
};

还有B.h：

#include "A.h"
struct B{
...
std::vector<A> as;
}

我有这个omp_declare_reduction：

#pragma omp declare reduction(merge : B : omp_out.as.insert(omp_out.as.end(), omp_in.as.begin(), omp_in.as.end()))

但是，我收到此错误（A=FindAffineShapeArgs 和 B=Wrapper）：

/usr/include/c++/5/bits/stl_algobase.h(564): error: function "FindAffineShapeArgs::operator=(const FindAffineShapeArgs &)" (declared implicitly) cannot be referenced -- it is a deleted function
        *--__result = std::move(*--__last);
                    ^
          detected during:
            instantiation of "_BI2 std::__copy_move_backward<true, false, std::random_access_iterator_tag>::__copy_move_b(_BI1, _BI1, _BI2) [with _BI1=FindAffineShapeArgs *, _BI2=FindAffineShapeArgs *]" at line 606
            instantiation of "_BI2 std::__copy_move_backward_a<_IsMove,_BI1,_BI2>(_BI1, _BI1, _BI2) [with _IsMove=true, _BI1=FindAffineShapeArgs *, _BI2=FindAffineShapeArgs *]" at line 615
            instantiation of "_BI2 std::__copy_move_backward_a2<_IsMove,_BI1,_BI2>(_BI1, _BI1, _BI2) [with _IsMove=true, _BI1=FindAffineShapeArgs *, _BI2=FindAffineShapeArgs *]" at line 686
            instantiation of "_BI2 std::move_backward(_BI1, _BI1, _BI2) [with _BI1=FindAffineShapeArgs *, _BI2=FindAffineShapeArgs *]" at line 636 of "/usr/include/c++/5/bits/vector.tcc"
            instantiation of "void std::vector<_Tp, _Alloc>::_M_range_insert(std::vector<_Tp, _Alloc>::iterator, _ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _Tp=FindAffineShapeArgs, _Alloc=std::allocator<FindAffineShapeArgs>, _ForwardIterator=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>]" at line 1377 of "/usr/include/c++/5/bits/stl_vector.h"
            instantiation of "void std::vector<_Tp, _Alloc>::_M_insert_dispatch(std::vector<_Tp, _Alloc>::iterator, _InputIterator, _InputIterator, std::__false_type) [with _Tp=FindAffineShapeArgs, _Alloc=std::allocator<FindAffineShapeArgs>, _InputIterator=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>]" at line 1100 of "/usr/include/c++/5/bits/stl_vector.h"
            instantiation of "std::vector<_Tp, _Alloc>::iterator std::vector<_Tp, _Alloc>::insert(std::vector<_Tp, _Alloc>::const_iterator, _InputIterator, _InputIterator) [with _Tp=FindAffineShapeArgs, _Alloc=std::allocator<FindAffineShapeArgs>, _InputIterator=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>, <unnamed>=void]" at line 345 of
                      "/home/luca/Dropbox/HKUST/CloudCache/cloudcache/CloudCache/Descriptors/hesaff/pyramid.cpp"

    /usr/include/c++/5/bits/stl_algobase.h(340): error: function "FindAffineShapeArgs::operator=(const FindAffineShapeArgs &)" (declared implicitly) cannot be referenced -- it is a deleted function
              *__result = *__first;
                        ^
              detected during:
                instantiation of "_OI std::__copy_move<false, false, std::random_access_iterator_tag>::__copy_m(_II, _II, _OI) [with _II=FindAffineShapeArgs *, _OI=FindAffineShapeArgs *]" at line 402
                instantiation of "_OI std::__copy_move_a<_IsMove,_II,_OI>(_II, _II, _OI) [with _IsMove=false, _II=FindAffineShapeArgs *, _OI=FindAffineShapeArgs *]" at line 440
                instantiation of "_OI std::__copy_move_a2<_IsMove,_II,_OI>(_II, _II, _OI) [with _IsMove=false, _II=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>, _OI=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>]" at line 472
                instantiation of "_OI std::copy(_II, _II, _OI) [with _II=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>, _OI=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>]" at line 637 of "/usr/include/c++/5/bits/vector.tcc"
                instantiation of "void std::vector<_Tp, _Alloc>::_M_range_insert(std::vector<_Tp, _Alloc>::iterator, _ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _Tp=FindAffineShapeArgs, _Alloc=std::allocator<FindAffineShapeArgs>, _ForwardIterator=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>]" at line 1377 of "/usr/include/c++/5/bits/stl_vector.h"
                instantiation of "void std::vector<_Tp, _Alloc>::_M_insert_dispatch(std::vector<_Tp, _Alloc>::iterator, _InputIterator, _InputIterator, std::__false_type) [with _Tp=FindAffineShapeArgs, _Alloc=std::allocator<FindAffineShapeArgs>, _InputIterator=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>]" at line 1100 of "/usr/include/c++/5/bits/stl_vector.h"
                instantiation of "std::vector<_Tp, _Alloc>::iterator std::vector<_Tp, _Alloc>::insert(std::vector<_Tp, _Alloc>::const_iterator, _InputIterator, _InputIterator) [with _Tp=FindAffineShapeArgs, _Alloc=std::allocator<FindAffineShapeArgs>, _InputIterator=__gnu_cxx::__normal_iterator<FindAffineShapeArgs *, std::vector<FindAffineShapeArgs, std::allocator<FindAffineShapeArgs>>>, <unnamed>=void]" at line 345 of
                          "/home/luca/Dropbox/HKUST/CloudCache/cloudcache/CloudCache/Descriptors/hesaff/pyramid.cpp"

    compilation aborted for /home/luca/Dropbox/HKUST/CloudCache/cloudcache/CloudCache/Descriptors/hesaff/pyramid.cpp (code 2)

为什么会这样？这可能与this 有关，但情况不同。

Answer 1

这与 omp 或明显的循环引用无关（这里的循环引用 per se 没有任何问题）。您将收到类似的编译错误：

#include <vector>

struct B {};

struct A
{
    A(B &b) :
        b(b) {}

    B &b;
};


B b;
A a{b}, aa{b};

void foo()
{
        a=aa;
}

gcc 错误的消息，在这种情况下，会给你指出线索：

t.C:19:4: error: use of deleted function ‘A& A::operator=(const A&)’

包含引用的类没有默认赋值运算符。这是因为引用不能在传统意义上被更改或“分配给”。

您正在创建一个std::vector，它需要根据需要复制/移动其值。但是向量的类包含一个引用成员，它将类的赋值运算符从高轨道上删除。

为了实现这一点，您需要为A 类定义自己的赋值运算符和/或复制构造函数，并让它们执行您需要它们执行的操作。