使用默认复制构造函数时出错："deleted function"

Error using defaulted copy constructor: "deleted function"

本文关键字：deleted function 出错 默认 复制 构造函数      更新时间：2023-10-16

我正在使用g++ 5.1.0编译以下c++ 14程序test.cpp:

#include <memory>
class Factor {
  public:
    Factor(const Factor&) = default;
    Factor(Factor&&) = default;
    Factor& operator=(const Factor&) = default;
    Factor& operator=(Factor&&) = default;
    Factor(int data) { 
      _data = std::make_unique<int>(data);
    }
    int* data() const { return _data.get(); }
  private:
    std::unique_ptr<int> _data;
};
class Node {
  public:
    Node(const Node& other) : _factor(other._factor) {
    }
  private:
    Factor _factor;
};
int main(int argc, char **argv) {
}

当我尝试编译时，我得到以下错误:

test.cpp: In copy constructor ‘Node::Node(const Node&)’:
test.cpp:19:52: error: use of deleted function ‘Factor::Factor(const Factor&)’
     Node(const Node& other) : _factor(other._factor) {
                                                    ^
test.cpp:5:5: note: ‘Factor::Factor(const Factor&)’ is implicitly deleted because the default definition would be ill-formed:
     Factor(const Factor&) = default;
     ^
test.cpp:5:5: error: use of deleted function ‘std::unique_ptr<_Tp, _Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = int; _Dp = std::default_delete<int>]’
In file included from /usr/include/c++/5/memory:81:0,
                 from test.cpp:1:
/usr/include/c++/5/bits/unique_ptr.h:356:7: note: declared here
       unique_ptr(const unique_ptr&) = delete;
       ^

我不知道从哪里开始诊断这个问题，因为对我来说，复制构造函数存在并且没有被删除似乎相当明显。这可能是什么原因呢?

正如juanchopanza所指出的，这是由于Factor类中不可复制的std::unique_ptr数据成员导致复制构造函数被静默删除。

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