无法将 std::vector<bool> 传递给 winrt::array_view

Question

我试图通过 C++/WinRT 库使用 Windows::Gaming::Input::RawGameController。

调用RawGameController::GetCurrentReading()获取当前控制器状态：

std::vector<bool> buttonsArray(rawController.ButtonCount(), false);
std::vector<GameControllerSwitchPosition> switchesArray(rawController.SwitchCount(), GameControllerSwitchPosition::Center);
std::vector<double> axisArray(rawController.AxisCount(), 0.0);
uint64_t timestamp = rawController.GetCurrentReading(buttonsArray, switchesArray, axisArray);

并且有编译错误：

1>------ Build started: Project: cppwinrtgamepad, Configuration: Debug x64 ------
1>cppwinrtgamepad.cpp
1>c:\somepath\x64\debug\generated files\winrt\base.h(3458): error C2039: 'data': is not a member of 'std::vector<T,std::allocator<_Ty>>'
1>        with
1>        [
1>            T=bool,
1>            _Ty=bool
1>        ]
1>c:\somepath\x64\debug\generated files\winrt\base.h(3663): note: see declaration of 'std::vector<T,std::allocator<_Ty>>'
1>        with
1>        [
1>            T=bool,
1>            _Ty=bool
1>        ]
1>c:\somepath\cppwinrtgamepad.cpp(121): note: see reference to function template instantiation 'winrt::array_view<T>::array_view<T>(std::vector<T,std::allocator<_Ty>> &) noexcept' being compiled
1>        with
1>        [
1>            T=bool,
1>            _Ty=bool
1>        ]
1>c:\somepath\cppwinrtgamepad.cpp(121): note: see reference to function template instantiation 'winrt::array_view<T>::array_view<T>(std::vector<T,std::allocator<_Ty>> &) noexcept' being compiled
1>        with
1>        [
1>            T=bool,
1>            _Ty=bool
1>        ]
1>c:\somepath\cppwinrtgamepad.cpp(90): note: see reference to class template instantiation 'winrt::impl::fast_iterator<winrt::Windows::Foundation::Collections::IVectorView<winrt::Windows::Gaming::Input::Gamepad>>' being compiled
1>c:\somepath\x64\debug\generated files\winrt\base.h(7801): note: see reference to class template instantiation 'winrt::com_ptr<winrt::impl::IContextCallback>' being compiled
1>c:\somepath\x64\debug\generated files\winrt\base.h(7573): note: see reference to class template instantiation 'winrt::com_ptr<winrt::impl::IServerSecurity>' being compiled
1>c:\somepath\x64\debug\generated files\winrt\base.h(7532): note: see reference to class template instantiation 'std::chrono::time_point<winrt::clock,winrt::Windows::Foundation::TimeSpan>' being compiled
1>c:\somepath\x64\debug\generated files\winrt\base.h(5264): note: see reference to class template instantiation 'winrt::com_ptr<winrt::impl::IMarshal>' being compiled
1>c:\somepath\x64\debug\generated files\winrt\base.h(2503): note: see reference to class template instantiation 'winrt::com_ptr<To>' being compiled
1>        with
1>        [
1>            To=winrt::impl::ILanguageExceptionErrorInfo2
1>        ]
1>c:\somepath\x64\debug\generated files\winrt\base.h(4120): note: see reference to function template instantiation 'winrt::com_ptr<To> winrt::com_ptr<winrt::impl::IRestrictedErrorInfo>::try_as<winrt::impl::ILanguageExceptionErrorInfo2>(void) noexcept const' being compiled
1>        with
1>        [
1>            To=winrt::impl::ILanguageExceptionErrorInfo2
1>        ]
1>c:\somepath\x64\debug\generated files\winrt\base.h(4202): note: see reference to class template instantiation 'winrt::com_ptr<winrt::impl::IRestrictedErrorInfo>' being compiled
1>c:\program files (x86)\microsoft visual studio\2017\professional\vc\tools\msvc\14.16.27023\include\string_view(39): note: see reference to class template instantiation 'std::basic_string_view<wchar_t,std::char_traits<wchar_t>>' being compiled
1>c:\somepath\x64\debug\generated files\winrt\base.h(3458): error C2664: 'winrt::array_view<T>::array_view(winrt::array_view<T> &&)': cannot convert argument 1 from 'winrt::array_view<T>::size_type' to 'std::initializer_list<bool>'
1>        with
1>        [
1>            T=bool
1>        ]
1>c:\somepath\x64\debug\generated files\winrt\base.h(3459): note: No constructor could take the source type, or constructor overload resolution was ambiguous
1>Done building project "cppwinrtgamepad.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

GetCurrentReading() 在winrt/Windows.Gaming.Input.h 中定义如下：

template <typename D> uint64_t consume_Windows_Gaming_Input_IRawGameController<D>::GetCurrentReading(array_view<bool> buttonArray, array_view<Windows::Gaming::Input::GameControllerSwitchPosition> switchArray, array_view<double> axisArray) const

而对应的winrt::array_view构造函数在winrt/base.h中定义如下：

template <typename C>
array_view(std::vector<C>& value) noexcept :
    array_view(value.data(), static_cast<size_type>(value.size()))
{}

考虑到std::vector<bool> 根本不限制data() 方法，这看起来像是一个不经意的错误。 或者有其他推荐的方式拨打RawGameController::GetCurrentReading()？

PS：作为一种解决方法，我可以使用std::array<bool, SOME_BIG_BUTTTON_COUNT>，但它太丑了。

Answer 1

这是设计使然。 winrt::array_view 是一个适配器，它告诉底层 API 绑定的数组或存储具有适当的二进制布局，可以有效地接收数据（通常通过 memcpy），而无需进行某种转换。 std::vector<bool> 不提供该保证，因此无法使用。您可能想尝试其他方法，例如 std::array 或其他一些连续容器。

Answer 2

std::vector<bool> 中的每个元素占用一个位而不是 sizeof(bool) 字节。它不一定将其元素存储为连续数组，因此不包含 data() 方法。我有一个工作代码，但是这不是最佳解决方案。您可以尝试使用 bool b[] 方法创建 bool 数组。

bool buttonsArray[]{ rawController.ButtonCount(), false };
std::vector<GameControllerSwitchPosition> switchesArray(rawController.SwitchCount(), GameControllerSwitchPosition::Center);
std::vector<double> axisArray(rawController.AxisCount(), 0.0);
uint64_t timestamp = rawController.GetCurrentReading(buttonsArray, switchesArray, axisArray);

Answer 3

丑陋的解决方法，而不是使用vector<bool>：

int32_t buttons = rawController.ButtonCount();
int32_t switches = rawController.SwitchCount();
int32_t axis = rawController.AxisCount();

std::unique_ptr<bool[]> buttonsArray = std::make_unique<bool[]>(buttons);
std::vector<GameControllerSwitchPosition> switchesArray(switches);
std::vector<double> axisArray(axis);

uint64_t timestamp = rawController.GetCurrentReading(winrt::array_view<bool>(buttonsArray.get(), buttonsArray.get() + buttons), switchesArray, axisArray);