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正确的语法将unique_ptr分配给新的boost::asio::io_service::work object?

unique-ptr boost-asio syntax c++

Dronz · 技术社区 · 11 年前

分配 std::unique_ptr<boost::asio::io_service::work> 指向新的 boost::asio::io_service::work 对象

我正在转换 boost::asio 从使用静态函数和全局变量到类实现的代码,但这意味着我必须替换工作初始化:

std::unique_ptr<boost::asio::io_service::work> KeepAlive(
  new boost::asio::io_service::work(TheASIOService));

类定义中包含类成员变量:

std::unique_ptr<boost::asio::io_service::work> KeepAlive;

稍后分配给新值:

KeepAlive = new boost::asio::io_service::work(IO_Service);

编译器根据参数类型(Boost错误的括号)拒绝:

g++ -std=c++0x -c -Wall ../comms/CommServer.cpp
../comms/CommServer.cpp: In member function âvoid CommServer::Listen()â:
../comms/CommServer.cpp:39:13: error: no match for âoperator=â (operand types are âstd::unique_ptr<boost::asio::io_service::work>â and âboost::asio::io_service::work*â)
   KeepAlive = new boost::asio::io_service::work(IO_Service);
             ^
../comms/CommServer.cpp:39:13: note: candidates are:
In file included from /usr/include/c++/4.8/memory:81:0,
                 from /usr/include/boost/config/no_tr1/memory.hpp:21,
                 from /usr/include/boost/get_pointer.hpp:14,
                 from /usr/include/boost/bind/mem_fn.hpp:25,
                 from /usr/include/boost/mem_fn.hpp:22,
                 from /usr/include/boost/bind/bind.hpp:26,
                 from /usr/include/boost/bind.hpp:22,
                 from ../comms/Comms.h:16,
                 from ../comms/CommServer.h:16,
                 from ../comms/CommServer.cpp:10:
/usr/include/c++/4.8/bits/unique_ptr.h:190:7: note: std::unique_ptr<_Tp, _Dp>& std::unique_ptr<_Tp, _Dp>::operator=(std::unique_ptr<_Tp, _Dp>&&) [with _Tp = boost::asio::io_service::work; _Dp = std::default_delete<boost::asio::io_service::work>]
       operator=(unique_ptr&& __u) noexcept
       ^
/usr/include/c++/4.8/bits/unique_ptr.h:190:7: note:   no known conversion for argument 1 from âboost::asio::io_service::work*â to âstd::unique_ptr<boost::asio::io_service::work>&&â
/usr/include/c++/4.8/bits/unique_ptr.h:203:2: note: template<class _Up, class _Ep> typename std::enable_if<std::__and_<std::is_convertible<typename std::unique_ptr<_Up, _Ep>::pointer, typename std::unique_ptr<_Tp, _Dp>::_Pointer::type>, std::__not_<std::is_array<_Up> > >::value, std::unique_ptr<_Tp, _Dp>&>::type std::unique_ptr<_Tp, _Dp>::operator=(std::unique_ptr<_Up, _Ep>&&) [with _Up = _Up; _Ep = _Ep; _Tp = boost::asio::io_service::work; _Dp = std::default_delete<boost::asio::io_service::work>]
  operator=(unique_ptr<_Up, _Ep>&& __u) noexcept
  ^
/usr/include/c++/4.8/bits/unique_ptr.h:203:2: note:   template argument deduction/substitution failed:
../comms/CommServer.cpp:39:13: note:   mismatched types âstd::unique_ptr<_Tp, _Dp>â and âboost::asio::io_service::work*â
   KeepAlive = new boost::asio::io_service::work(IO_Service);
             ^
In file included from /usr/include/c++/4.8/memory:81:0,
                 from /usr/include/boost/config/no_tr1/memory.hpp:21,
                 from /usr/include/boost/get_pointer.hpp:14,
                 from /usr/include/boost/bind/mem_fn.hpp:25,
                 from /usr/include/boost/mem_fn.hpp:22,
                 from /usr/include/boost/bind/bind.hpp:26,
                 from /usr/include/boost/bind.hpp:22,
                 from ../comms/Comms.h:16,
                 from ../comms/CommServer.h:16,
                 from ../comms/CommServer.cpp:10:
/usr/include/c++/4.8/bits/unique_ptr.h:211:7: note: std::unique_ptr<_Tp, _Dp>& std::unique_ptr<_Tp, _Dp>::operator=(std::nullptr_t) [with _Tp = boost::asio::io_service::work; _Dp = std::default_delete<boost::asio::io_service::work>; std::nullptr_t = std::nullptr_t]
       operator=(nullptr_t) noexcept
       ^
/usr/include/c++/4.8/bits/unique_ptr.h:211:7: note:   no known conversion for argument 1 from âboost::asio::io_service::work*â to âstd::nullptr_tâ

我检查了 documentation for the unique_ptr's assignment operator 并看到该示例出于某种原因在对 std::move() ,但编译器以类似的方式对此犹豫不决:

g++ -std=c++0x -c -Wall ../comms/CommServer.cpp
../comms/CommServer.cpp: In member function âvoid CommServer::Listen()â:
../comms/CommServer.cpp:39:13: error: no match for âoperator=â (operand types are âstd::unique_ptr<boost::asio::io_service::work>â and âstd::remove_reference<boost::asio::io_service::work*>::type {aka boost::asio::io_service::work*}â)
   KeepAlive = std::move(new boost::asio::io_service::work(IO_Service));
             ^
../comms/CommServer.cpp:39:13: note: candidates are:
In file included from /usr/include/c++/4.8/memory:81:0,
                 from /usr/include/boost/config/no_tr1/memory.hpp:21,
                 from /usr/include/boost/get_pointer.hpp:14,
                 from /usr/include/boost/bind/mem_fn.hpp:25,
                 from /usr/include/boost/mem_fn.hpp:22,
                 from /usr/include/boost/bind/bind.hpp:26,
                 from /usr/include/boost/bind.hpp:22,
                 from ../comms/Comms.h:16,
                 from ../comms/CommServer.h:16,
                 from ../comms/CommServer.cpp:10:
/usr/include/c++/4.8/bits/unique_ptr.h:190:7: note: std::unique_ptr<_Tp, _Dp>& std::unique_ptr<_Tp, _Dp>::operator=(std::unique_ptr<_Tp, _Dp>&&) [with _Tp = boost::asio::io_service::work; _Dp = std::default_delete<boost::asio::io_service::work>]
       operator=(unique_ptr&& __u) noexcept
       ^
/usr/include/c++/4.8/bits/unique_ptr.h:190:7: note:   no known conversion for argument 1 from âstd::remove_reference<boost::asio::io_service::work*>::type {aka boost::asio::io_service::work*}â to âstd::unique_ptr<boost::asio::io_service::work>&&â
/usr/include/c++/4.8/bits/unique_ptr.h:203:2: note: template<class _Up, class _Ep> typename std::enable_if<std::__and_<std::is_convertible<typename std::unique_ptr<_Up, _Ep>::pointer, typename std::unique_ptr<_Tp, _Dp>::_Pointer::type>, std::__not_<std::is_array<_Up> > >::value, std::unique_ptr<_Tp, _Dp>&>::type std::unique_ptr<_Tp, _Dp>::operator=(std::unique_ptr<_Up, _Ep>&&) [with _Up = _Up; _Ep = _Ep; _Tp = boost::asio::io_service::work; _Dp = std::default_delete<boost::asio::io_service::work>]
  operator=(unique_ptr<_Up, _Ep>&& __u) noexcept
  ^
/usr/include/c++/4.8/bits/unique_ptr.h:203:2: note:   template argument deduction/substitution failed:
../comms/CommServer.cpp:39:13: note:   mismatched types âstd::unique_ptr<_Tp, _Dp>â and âstd::remove_reference<boost::asio::io_service::work*>::type {aka boost::asio::io_service::work*}â
   KeepAlive = std::move(new boost::asio::io_service::work(IO_Service));
             ^
In file included from /usr/include/c++/4.8/memory:81:0,
                 from /usr/include/boost/config/no_tr1/memory.hpp:21,
                 from /usr/include/boost/get_pointer.hpp:14,
                 from /usr/include/boost/bind/mem_fn.hpp:25,
                 from /usr/include/boost/mem_fn.hpp:22,
                 from /usr/include/boost/bind/bind.hpp:26,
                 from /usr/include/boost/bind.hpp:22,
                 from ../comms/Comms.h:16,
                 from ../comms/CommServer.h:16,
                 from ../comms/CommServer.cpp:10:
/usr/include/c++/4.8/bits/unique_ptr.h:211:7: note: std::unique_ptr<_Tp, _Dp>& std::unique_ptr<_Tp, _Dp>::operator=(std::nullptr_t) [with _Tp = boost::asio::io_service::work; _Dp = std::default_delete<boost::asio::io_service::work>; std::nullptr_t = std::nullptr_t]
       operator=(nullptr_t) noexcept
       ^
/usr/include/c++/4.8/bits/unique_ptr.h:211:7: note:   no known conversion for argument 1 from âstd::remove_reference<boost::asio::io_service::work*>::type {aka boost::asio::io_service::work*}â to âstd::nullptr_tâ

阅读上的文档 std::move ,我发现有一些新的指针概念我不太熟悉,应该仔细阅读,但在那之前,我更希望 ::work 对象

这是吗 unique_ptr 保护我不做会使担保失效的事?我不应该使用 唯一_ptr 在这里或者我只是没有正确的语法?我应该使用 unique_ptr::reset(new ...) ?

2 回复 | 直到 11 年前

David 11 年前

使用 unique_ptr::reset :

keepAlive.reset(new boost::asio::io_service::work(IO_Service));

对于延迟构造使用unique_ptr是有效的,尽管使用std/boost更理想 optional 除非你也明确需要/想要动态分配它。我还要注意,你应该尝试设计你的类,这样你就可以在构造函数中完全构造所有的东西,而不需要延迟构造。但有时这是不可避免的。

Walter 11 年前

查看以下文档 std::unique_ptr<> 。你会发现的 unique_ptr<>::reset() 是您的朋友:

KeepAlive.reset(new boost::asio::io_service::work(IO_Service));