如何使用初始化列表创建 QSharedPointer<QMap<a,b>>？

Question

什么有效

在 Qt 5.12.4 中，我尝试动态创建 QSharedPointer<QMap<int,bool>>。我知道我能做到

QMap<int, bool> mp = { { 1, true } };

以及动态

QMap<int, bool>* mpptr = new QMap<int, bool> { { 1, false } };

我知道我可以像这样创建我的 QSharedPointer：

QMap<int, bool>* mpptr = new QMap<int, bool> { { 1, false } };
        QSharedPointer<QMap<int, bool>> shraredmpptr(mpptr);

什么没有

我想一次完成，但我无法完成。我试过最明显的

QSharedPointer<QMap<int, bool>> mpsptr =
            QSharedPointer<QMap<int, bool>>::create(new QMap<int, bool> { { 1, false } });

但无济于事。编译器警告我我的类型不匹配，但我没有看到必须更改代码才能编译的地方。有任何想法吗？提前致谢。

编译器错误

In file included from D:\Qt.12.4\mingw73_64\include/QtCore/qsharedpointer.h:48:0,
                 from D:\Qt.12.4\mingw73_64\include/QtCore/qdebug.h:54,
                 from D:\Qt.12.4\mingw73_64\include\QtCore/qloggingcategory.h:44,
                 from D:\Qt.12.4\mingw73_64\include\QtCore/QLoggingCategory:1,
                 from ..\..\..\..\myLibsQt\src\libs/a/foo.h:4,
                 from ..\..\..\..\myLibsQt\src\libs/a/bar.h:8,
                 from ..\..\..\..\myLibsQt\src\libs/b/baz.h:8,
                 from ..\..\..\..\myLibsQt\src\libs/c/bla.h:8,
                 from ..\..\..\..\myLibsQt\src\libs\c\blubb.cpp:1:
D:\Qt.12.4\mingw73_64\include/QtCore/qsharedpointer_impl.h: In instantiation of 'static QSharedPointer<T> QSharedPointer<T>::create(Args&& ...) [with Args = {QMap<int, bool>*}; T = QMap<int, bool>]':
..\..\..\..\myLibsQt\src\libs\c\blubb.cpp:27:80:   required from here
D:\Qt.12.4\mingw73_64\include/QtCore/qsharedpointer_impl.h:445:9: error: no matching function for call to 'QMap<int, bool>::QMap(QMap<int, bool>*)'
         new (ptr) T(std::forward<Args>(arguments)...);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from D:\Qt.12.4\mingw73_64\include/QtCore/qdebug.h:47:0,
                 from D:\Qt.12.4\mingw73_64\include\QtCore/qloggingcategory.h:44,
                 from D:\Qt.12.4\mingw73_64\include\QtCore/QLoggingCategory:1,
                 from ..\..\..\..\myLibsQt\src\libs/a/foo.h:4,
                 from ..\..\..\..\myLibsQt\src\libs/a/bar.h:8,
                 from ..\..\..\..\myLibsQt\src\libs/b/baz.h:8,
                 from ..\..\..\..\myLibsQt\src\libs/c/bla.h:8,
                 from ..\..\..\..\myLibsQt\src\libs\c\blubb.cpp:1:
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:1164:22: note: candidate: QMap<K, V>::QMap(const std::map<Key, T>&) [with Key = int; T = bool]
 Q_OUTOFLINE_TEMPLATE QMap<Key, T>::QMap(const std::map<Key, T> &other)
                      ^~~~~~~~~~~~
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:1164:22: note:   no known conversion for argument 1 from 'QMap<int, bool>*' to 'const std::map<int, bool, std::less<int>, std::allocator<std::pair<const int, bool> > >&'
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:343:12: note: candidate: QMap<K, V>::QMap(QMap<K, V>&&) [with Key = int; T = bool]
     inline QMap(QMap<Key, T> &&other) Q_DECL_NOTHROW
            ^~~~
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:343:12: note:   no known conversion for argument 1 from 'QMap<int, bool>*' to 'QMap<int, bool>&&'
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:622:8: note: candidate: QMap<K, V>::QMap(const QMap<K, V>&) [with Key = int; T = bool]
 inline QMap<Key, T>::QMap(const QMap<Key, T> &other)
        ^~~~~~~~~~~~
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:622:8: note:   no known conversion for argument 1 from 'QMap<int, bool>*' to 'const QMap<int, bool>&'
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:330:12: note: candidate: QMap<K, V>::QMap(std::initializer_list<std::pair<_T1, _T2> >) [with Key = int; T = bool]
     inline QMap(std::initializer_list<std::pair<Key,T> > list)
            ^~~~
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:330:12: note:   no known conversion for argument 1 from 'QMap<int, bool>*' to 'std::initializer_list<std::pair<int, bool> >'
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:328:12: note: candidate: QMap<K, V>::QMap() [with Key = int; T = bool]
     inline QMap() Q_DECL_NOTHROW : d(static_cast<QMapData<Key, T> *>(const_cast<QMapDataBase *>(&QMapDataBase::shared_null))) { }
            ^~~~
D:\Qt.12.4\mingw73_64\include/QtCore/qmap.h:328:12: note:   candidate expects 0 arguments, 1 provided
mingw32-make[1]: *** [Makefile.Debug:1488: debug/blubb.o] Error 1

Answer 1

好的，我找到了适合我的答案。上面的没有用 msvc17 和我的 arm 工具链编译。我的第一种方法也会产生内存泄漏。

正确的做法是

QSharedPointer<QMap<int, bool>> mpsptr(new QMap<int, bool> { { 1, false } });

Answer 2

传递给 create 的参数被直接传递给构造函数。因此，您可以这样做：

QSharedPointer<QMap<int, bool>> mpsptr =  QSharedPointer<QMap<int, bool>>::create({
  { 1, false }
});

如果您使用 C++11 或更高版本，为什么不使用 auto ？

auto mpsptr =  QSharedPointer<QMap<int, bool>>::create({
  { 1, false }
});

Answer 3

这对我有用（使用 GCC、C++ x86 64 位 编译）：

QSharedPointer<QMap<int, bool>> mpsptr = QSharedPointer<QMap<int, bool>>::create(QMap<int, bool>{{1, false}});

如何使用初始化列表创建 QSharedPointer<QMap<a,b>>？

How to create a QSharedPointer<QMap<a,b>> with an initializer list?

qt

c++11

qmap

qsharedpointer

什么有效

什么没有

编译器错误