Question

我在for循环中有以下内容，编译器说'operator = is ambiguous'。不知道如何解决这个问题，任何人都可以帮忙吗？

rootelement = document->getDocumentElement();
    boost::interprocess::unique_ptr<DOMNodeIterator, release_deleter> itera (document->createNodeIterator(rootelement, DOMNodeFilter::SHOW_ALL, NULL, true));
    for(boost::interprocess::unique_ptr<DOMNode, release_deleter> current (itera->nextNode()); current != 0; current = boost::interprocess::unique_ptr<DOMNode, release_deleter> (itera->nextNode()))  // Last assignment on current is ambiguous

完整错误：

*

\XMLDocument.cpp(193) : error C2593: 'operator =' is ambiguous
        c:\Program Files\boost\boost_1_44\boost\interprocess\smart_ptr\unique_ptr.hpp(249): could be 'boost::interprocess::unique_ptr<T,D> &boost::interprocess::unique_ptr<T,D>::operator =(int boost::interprocess::unique_ptr<T,D>::nat::* )'
        with
        [
            T=xercesc_3_1::DOMNode,
            D=release_deleter
        ]
        unique_ptr.hpp(211): or       'boost::interprocess::unique_ptr<T,D> &boost::interprocess::unique_ptr<T,D>::operator =(boost::interprocess::rv<boost::interprocess::unique_ptr<T,D>> &)'
        with
        [
            T=xercesc_3_1::DOMNode,
            D=release_deleter
        ]
        while trying to match the argument list '(boost::interprocess::unique_ptr<T,D>, boost::interprocess::unique_ptr<T,D>)'
        with
        [
            T=xercesc_3_1::DOMNode,
            D=release_deleter
        ]
        and
        [
            T=xercesc_3_1::DOMNode,
            D=release_deleter
        ]
  \XMLDocument.cpp(193) : see reference to class template instantiation 'boost::interprocess::detail::unique_ptr_error<T>' being compiled
        with
        [
            T=boost::interprocess::unique_ptr<xercesc_3_1::DOMNode,release_deleter>
        ]
    XMLDocument.cpp(193) : see reference to class template instantiation 'boost::interprocess::detail::unique_ptr_error<T>' being compiled
        with
        [
            T=xercesc_3_1::DOMNode *
        ]
       \XMLDocument.cpp(193) : see reference to class template instantiation 'boost::interprocess::detail::unique_ptr_error<T>' being compiled
        with
        [
            T=xercesc_3_1::DOMNode *
        ]
        XMLDocument.cpp(192) : see reference to class template instantiation 'boost::int
erprocess::detail::unique_ptr_error<T>' being compiled
        with
        [
            T=xercesc_3_1::DOMNodeIterator *
        ]

*

Answer 1

与Stephane一样，unique_ptr保持唯一性，除非您明确移动它们，或为它们分配右值。通常情况下，你的代码会没问题，但是因为你伪造rvalues，你需要明确地移动它。

我从未使用boost::interprocess::unique_ptr，但看起来你想要这个：

namespace bi = boost::interprocess; // do these please!
typedef bi::unique_ptr<DOMNode, release_deleter> node_ptr;
typedef bi::unique_ptr<DOMNodeIterator, release_deleter> iterator_ptr;

rootelement = document->getDocumentElement();
iterator_ptr itera(document->createNodeIterator(rootelement,
                                           DOMNodeFilter::SHOW_ALL, NULL, true));

for (node_ptr current(itera->nextNode()); current != 0;
         current = bi::move(node_ptr(itera->nextNode())))

更简单可能是：

for (node_ptr current(itera->nextNode()); current != 0;
         current.reset(itera->nextNode()))

Answer 2

我认为只能通过调用std :: move（）来分配std :: unique_ptr。这是它明显失去底层对象所有权的方式。

std ::unique_ptr<T> upOldT = new T ;
std ::unique_ptr<T> pT = std ::move(upOldT) ;

正如GMan所说，C ++ 0x还不是当前的C ++标准，所以它应该是 boost :: interprocess :: unique_ptr ...

Answer 3

我不确定，也没有尝试过，但你可以尝试：

current = itera->nextNode()

然后它只会带来一个含糊之处。

Operator =不明确（C ++）

3 个答案: