【发布时间】：2021-12-25 05:09:09
【问题描述】：
编写这些函数 get_m_source() 、 get_m_key() 和 get_m_data() 的正确方法是什么 我尝试了下面的第一种方法，因为返回的是 boost::optional。 但它导致了如下所示的错误-
/home/badri/sandboxes_git/acvs-illustra-global/output/amb_cv22_evk/arm/release/usr/include/boost/optional/optional.hpp: In instantiation of ‘void boost::optional_detail::optional_base<T>::construct(boost::optional_detail::optional_base<T>::argument_type) [with T = tev::events::EventItemCategory; boost::optional_detail::optional_base<T>::argument_type = const tev::events::EventItemCategory&]’:
/home/badri/sandboxes_git/acvs-illustra-global/output/amb_cv22_evk/arm/release/usr/include/boost/optional/optional.hpp:181:18: required from ‘boost::optional_detail::optional_base<T>::optional_base(const boost::optional_detail::optional_base<T>&) [with T = tev::events::EventItemCategory]’
/home/badri/sandboxes_git/acvs-illustra-global/output/amb_cv22_evk/arm/release/usr/include/boost/optional/optional.hpp:944:5: required from here
/home/badri/sandboxes_git/acvs-illustra-global/output/amb_cv22_evk/arm/release/usr/include/boost/optional/optional.hpp:384:8: error: use of deleted function ‘tev::events::EventItemCategory::EventItemCategory(const tev::events::EventItemCategory&)’
384 | ::new (m_storage.address()) value_type(val) ;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated due to -Wfatal-errors.
class EventMessage
{
public:
.
.
boost::optional<EventItemCategory> get_m_source() { return m_source; }
boost::optional<EventItemCategory> get_m_key() { return m_key; }
boost::optional<EventItemCategory> get_m_data() { return m_data; }
private:
void init();
boost::optional<EventItemCategory>& getEventItemCategory( EVENT_ITEM_CATEGORY_TYPE const& type );
time_t m_timestamp;
boost::optional<PROPERTY_OPERATION> m_propertyOperation;
boost::optional<EventItemCategory> m_source;
boost::optional<EventItemCategory> m_key;
boost::optional<EventItemCategory> m_data;
std::map<EVENT_ITEM_CATEGORY_TYPE const, boost::optional<EventItemCategory> & > m_eventItemMap;
};
我尝试了第二种方法，很清楚它不会起作用。正如预期的那样，抛出的错误是 -
./EventMessage.hpp:68:47: error: could not convert ‘((tev::events::EventMessage*)this)->tev::events::EventMessage::m_source’ from ‘boost::optional<tev::events::EventItemCategory>’ to ‘tev::events::EventItemCategory’
class EventMessage
{
public:
.
.
.
EventItemCategory get_m_source() { return m_source; }
EventItemCategory get_m_key() { return m_key; }
EventItemCategory get_m_data() { return m_data; }
private:
void init();
boost::optional<EventItemCategory>& getEventItemCategory( EVENT_ITEM_CATEGORY_TYPE const& type );
time_t m_timestamp;
boost::optional<PROPERTY_OPERATION> m_propertyOperation;
boost::optional<EventItemCategory> m_source;
boost::optional<EventItemCategory> m_key;
boost::optional<EventItemCategory> m_data;
std::map<EVENT_ITEM_CATEGORY_TYPE const, boost::optional<EventItemCategory> & > m_eventItemMap;
};
【问题讨论】：
-
我猜
EventItemCategory不可复制，请出示minimal reproducible example -
谢谢艾伦。我会得到一个。
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这是您的起点coliru.stacked-crooked.com/a/fb9c0d08f87a541a。只需编辑直到出现错误
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通过 MSVP，我收到了额外的说明，让您的怀疑正确，艾伦。 EventItemCategory.hpp:66:7: 注意：'EventItemCategory::EventItemCategory(const EventItemCategory&)' 被隐式声明为已删除，因为 'EventItemCategory' 声明了移动构造函数或移动赋值运算符类 EventItemCategory ^~~~~~~~~~~ ~~~~~~
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所以在这种情况下，我怎样才能执行相当于 boost::optional
get_m_source() { return m_source;我想要一个函数，例如 get_m_source() 以便我可以访问 m_source 以进行调试。