如何创建 QSharedPointer <qmap<a,b> &gt; 带有初始化列表？ </qmap<a,b>

Question

What works

In Qt 5.12.4, I try to dynamically create QSharedPointer<QMap<int,bool>> . I know that I can do

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

as well as dynamically with

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

I know that I can create my QSharedPointer like so:

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

What doesn't

I want do this in one single shot, which I am not able to accomplish. I tried the most obvious

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

but to no avail. The compiler gives me warnings that my types do not match but I do not see the point where I have to change the code so that it compiles. Any Ideas? Thanks in advance.

Compiler errors

In file included from D:\Qt\5.12.4\mingw73_64\include/QtCore/qsharedpointer.h:48:0,
                 from D:\Qt\5.12.4\mingw73_64\include/QtCore/qdebug.h:54,
                 from D:\Qt\5.12.4\mingw73_64\include\QtCore/qloggingcategory.h:44,
                 from D:\Qt\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\mingw73_64\include/QtCore/qdebug.h:47:0,
                 from D:\Qt\5.12.4\mingw73_64\include\QtCore/qloggingcategory.h:44,
                 from D:\Qt\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\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\5.12.4\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

The arguments passed to create are durectly passed to the constructor. Therefore, you can just do:

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

And if you use C++11 or above, why not use auto?

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

Answer 2

This worked for me (compiled with GCC, C++ x86 64bit ):

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

Answer 3

Ok, I found an answer that works for me. the above one did not compile with msvc17 and with my arm toolchain. Also my first approach produces a memory leak.

The correct way to do is is

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