Example. For example "sample: 45 2048". @xylosper said in How to manage QObject instance which is shared among lots of C++/QML places:. data(); delete obj; To copy to clipboard, switch view to plain text mode. So a conclusion would be: watch out for run-away. Detailed Description. The following chapters show an example and explain a few important details regarding the functionality and limits of the implementation. important difference that you have to explicitly call detach () to. QSharedDataPointer is a nifty way to implement copy-on-write and detaches/copies its object when it is accessed in a non-const way. The code the compiler generates for QScopedPointer is the same as when writing it manually. The problem is, that when implementing a QSharedAbstractItemModel, like the QAbstractListModel, you need to deal with raw pointers. Since that method takes a QSharedPointer<QCPAxisTicker>,. staticCast<Switch> (); Both versions are basically equivalent to doing static_cast on raw pointers. The QSharedPointer class holds a strong reference to a shared pointer. This allows a safely shared pointer that can be used on objects that get passed around by reference like in C#. Examples of such functions include std::static_pointer_cast, custom comparators, or predicates. All children of a deleted QObject are deleted as well. Returns a const pointer to the shared data object. is not possible perform some atomic operation on two threads with two core processor at the same time. C++ (Cpp) QSharedPointer::getEndPoint - 6 examples found. Check your Options in the drop-down menu of this sections header. QSharedPointer will delete the pointer it is holding when it goes out of scope, provided no other. It stores its items in adjacent memory locations and provides fast index-based access. There are not so much Qt examples and demos with QSharedPointer because of the general concept for memory management in Qt using parent–child hierarchy of QObject. Study Resources. h","path":"src/corelib/tools/qalgorithms. C++ (Cpp) QSharedPointer Examples. The following custom cleanup handlers exist: QScopedPointerDeleter - the default, deletes the pointer using delete. A base class that allows obtaining a QSharedPointer for an object already managed by a shared pointer. It is a bug if you put just a pointer to your item to QChache and at the same time such pointer is managed by QSharedPointer. ) summary refs log tree commit diff statsQMetaType::construct (), QMetaType::sizeOf (), and QMetaType::alignOf. That said, your stack trace is really strange:. to ensure that the pointers being compared are equal. h" typedef BlockingQueue<QByteArray> MessageQueue; class. That said, yo. h" int main(). Describes how the Qt Remote Objects establishes a direct connection using a static source. h","path":"src/corelib/tools/qalgorithms. It's a start. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1. The worker, its thread, and its copy of the data are deleted but through the signal a copy of data is saved and sent back to your main thread. h","contentType":"file. 1. See QWeakPointer::toStrongRef() for an example. But, it all depends on your use case. Only the MyClass object controlled by the QSharedPointer gets deleted. Example#1. This is the pattern that the automatic data collector will look for and parse. I just have a general question here. 9 on Ubuntu 18. To have that guarantee, use toStrongRef(), which returns a QSharedPointer object. QSharedPointer:: QSharedPointer (const QWeakPointer < T > &other) Creates a QSharedPointer by promoting the weak reference other to strong reference and sharing its pointer. Previously i had done this: Code: MyObject * object; // Subclass of QObject. Member Function Documentation QWeakPointer:: QWeakPointer (). /blocking_queue. It is usually best to use a mutex with a QMutexLocker since this makes it easy to ensure that locking and unlocking are performed consistently. The QSharedPointer is an automatic, shared pointer in C++. If it represents a type, it returns QMetaType::Int. See QWeakPointer::toStrongRef() for an example. A class derived from EmployeeData could override that function and return the. > If you don't believe this matters, see comment in qdatetime. , a reference counter placed outside the object). Commented defines are for "not compiling" parts. If this function can determine that the pointer has already been deleted, it returns nullptr. Code that makes use of delete are candidates for QScopedPointer usage (and if not, possibly another type of smart pointer such as QSharedPointer). @Yakk: Thanks for that, I've updated my answer to reflect your point. template parameter is not a base or a derived type from. qt. C++ (Cpp) QSharedPointer::direction - 6 examples found. I have QVector<QSharedPointer<SomeData> > DataVec as a field of one class in a big objected-oriented project. This is the same as vector. The pointed-to value in the Q_ASSERT will live until the statement finishes. I'd like to fill QSharedPointer<T> collection from QJsonArray (serialized Q_GADGETS) instance using universal function (template). Qt also provides QSharedPointer, an implementation of a reference-counted shared pointer object, which can be used to maintain a collection of references to an individual pointer. Here comes an example using Event (The complete code is in the event_example directory). Here is my class function: template<class T> QSharedPointer<T> getObjectWithId ( int id ) { QSharedPointer<SqlObject> obj = getObjectWithId ( T::staticMetaObject. Adding a Q_DECLARE_METATYPE () makes the type known to all template based functions, including QVariant. QSharedPointer will delete the pointer it is holding when it goes out of scope, provided no other. This blog post is the first in a series that will cover using OpenGL with Qt. }; Q_DECLARE_METATYPE (blabla) But this code is giving me Error: In copy constructor ‘QThread::QThread (const QThread&)’: instantiated from ‘void. g. That said, your stack trace is really strange:. For some reason, there are very few examples out there on how to use QSharedPointer, so i find myself posting here. Is this correct? Because the image is so large, I don't want do copies of it and I want it to stay alive until all the. QPointer is not a smart pointer. That said, your stack trace is really strange:. For example, canConvert(QMetaType::fromType<int>()) would return true when called on a variant containing a string because, in principle, QVariant is able to convert strings of numbers to integers. [quote author="situ117" date="1304279927"] I was reading about QSharedPointer in Qt. QSharedPointer works with forward declarations, so I'd guess you're using it incorrectly; consider giving a minimal example that can be compiled (and more importantly doesn't require us to guess about the types). You will need to delete it yourself: ~MyClass () { delete m_process. But, it all depends on your use case. If a ptr2's. . Since the replicas have the same properties, signals, and slots as were. According to the docs the QSharedPointer internals and the object are allocated in one single memory allocation, which could help reduce memory fragmentation in a long-running application. behaves exactly like a normal pointer for normal purposes, including respect for constness. It behaves exactly like a normal pointer for normal purposes, including respect for constness. Use qSharedPointerCast (): QSharedPointer <Switch> mySwitchTest= qSharedPointerCast<Switch> (myState); Or call staticCast () on the smart pointer: QSharedPointer <Switch> mySwitchTest= myState. Commented defines are for "not compiling" parts. QSharedPointer will delete the pointer it is holding when it goes out of scope, provided no other QSharedPointer objects are referencing it. But we don't use smart pointers in Qt much, due to parent-driven memory model. In many cases, that UB may be innocuous, but it is UB regardless. The pointer ptr becomes managed by this QSharedPointer and must not be passed to another QSharedPointer object or deleted. See also QSharedPointer and QPointer. to ensure that the pointers being compared are equal. Just a small addition. The same question about Qt equivalent - QSharedPointer. C++ (Cpp) QSharedPointer::isSelected - 12 examples found. QSharedDataPointer has a very specific use-case, which is where you want to share data between instances, with copy-on-write behaviour - that is, as soon as one instance, tries to modify it, it detaches and it now has it's own separate copy. e. Qt provides a number of thread synchronization constructs, you'll probably want to start with QMutex and learn more about thread-safety. On programm exit i have 2 destructor calls for GeTokenItem and one more that invokes acces violation. Unfortunately Google was unable to help me this time. It behaves exactly like a normal pointer for normal purposes, including respect for constness. QSharedPointer will attempt to perform an automatic t static_cast. For some reason, there are very few examples out there on how to use QSharedPointer, so i find myself posting here. A guarded pointer, QPointer<T>, behaves like a normal C++ pointer T *, except that it is automatically cleared when the referenced object is destroyed (unlike normal C++ pointers, which become "dangling pointers" in such cases). But, it all depends on your use case. I use C++17, GCC 7. . Qt Code: Switch view. QPointer<QHash<QString, QString> > foo ( new QHash<QString, QString> () ); If you really need (smart) pointers to containers, try QSharedPointer, which doesn't require the contained object to be of any specific type. Otherwise, the object deletes itself after emitting the signal. These are the top rated real world C++ (Cpp) examples of QSharedPointer::getShapes extracted from open source projects. Then, a new QSharedPointer object is created that references the same int object. For example: class ScriptInterface :publicQObject { Q_OBJECT //. All of QList's functionality also applies to QQueue. Examples at hotexamples. Create an object, and then use the serializer as follows:. There are several ways to avoid the problem in this particular example I can think of: change Test destructor to expect null m, write template template<typename T> inline T no_move (T&& tmp) {return tmp;}, explicitly create temporary Test object in assign, add getter for m and call it to force copying m (advised by Jarod42 ); MS Visual Studio. The object is destroyed and its memory deallocated when either of the following happens: the last remaining shared_ptr owning the object is destroyed; ; the last remaining shared_ptr. . There are not so much Qt examples and demos with QSharedPointer because of the general concept for memory management in Qt using parent–child hierarchy of QObject. The QObjectList class is defined in the <QObject> header file as the following: typedefQList<QObject*>QObjectList; The first child added is the first object in the list and the last child added is the last object in the list, i. Ah, when the function actually needs to manipulate the smart pointer itself. If you refactor your code so that all new operator are in lines like these, all your problems will be solved. A simple code that could reproduce the issue. Detailed Description. A more appropriate question would be why is Qt using raw pointers instead of smart pointers (be those Qt's or C++11's), and the reason for this is simple - those are new features, and even though Qt 5 has. This can be used to retrieve QMetaMethod and QMetaProperty and use them on a pointer of this type for example, as given by QVariant::data(). typedef QVector<QSharedPointer<Tester> > TestPointerVector;. But you might miss the more convenient BlockingQueue in Java/Python. The problem is that this code is creating a QSharedPointer from a raw pointer, which implies ownership of the object pointed to. If we have smart pointers in Qt, why old C type pointers are preferred ? Reply Quote 0. The purpose of this class is to lay the T object out next to the reference counts, saving one memory allocation per shared pointer. But I've not seen it much in use in source code of Examples and Demos. in Qt-using projects. Qt로 프로그래밍할 때 메모리 관리 문제 (메모리 관리 불량으로 인한 메모리 누수 및 버그. However, by that time, a. You can rate examples to help us improve the quality of examples. QSharedPointer. The one I used in my own answer does. For your concrete example, you could use a QList<QSharedPointer<MyClass>> for the model and use QWeakPointer<MyClass> in the drawable classes. QSharedPointer는 다른 QSharedPointer 객체가 이를 참조하지 않는 한 범위를 벗어날 때 보유하고 있는 포인터를 삭제합니다. append(QSharedPointer<MyObject>(new MyObject("first", 1))); list. at (x); Then I pass it around and do the work, then the pointer dies but I have an extra one in the list so everything's fine, right? I noticed the destructor of MyClass is. I want QSharedPointer nav = m->getINav (); to be in while loop itself as this is kind of dummy application for my real. It can happen, since QObject may be destroyed by its parent. To complicate it even more, all debugging traces were leading to. When a QObject is destroyed, it in turn destroys all objects it owns. I was reading about QSharedPointer in Qt. Your solution is simple. It cannot be used to dereference the pointer directly, but it can be used to verify if the pointer has been deleted or not in another context. But in addition, QQueue provides three convenience functions. These conversions are called in a shared object which is properly loaded at runtime. For instance, the method index returns a QModelIndex that takes a void pointer in the constructor, pointing to one of those. It provides a safer and easier way to manage dynamic memory allocation and deallocation by automatically managing the reference counting of a shared object. QWeakPointer objects can only be created by assignment from a QSharedPointer. You can rate examples to help us improve the quality of examples. These are the top rated real world C++ (Cpp) examples of QSharedPointer::StopTimer extracted from open source projects. Also, by overloading the operator, it's very easy to. QExplicitlySharedDataPointer, QScopedPointer, and QSharedPointer. Example: QPointer < QLabel > label = new QLabel ; label - > setText( "&Status:" );. If on the other hand %h is available, the minutes will wrap around to zero after 59 and the time will carry to the hour. 8. If you type is base on QObject, you have to take care to avoid double free if they have a parent. Call doc:QSharedPointer :: data () to get a pointer to the referenced class; Make sure the QML engine doesn't assume ownership: doc:QDeclarativeEngine :: setObjectOwnership (P). I'm dealing with a large image and am doing several different processes on the QImage. Commented defines are for "not compiling" parts. QSharedPointer will delete the pointer it is holding when it goes out of scope, provided no other QSharedPointer objects are referencing it. This works actually quite well (with some restrictions you have to have in mind). T must be a subclass of QObject. For example, one can have a list of QStrings QList<QSharedPointer<QString> > queue. The QSharedPointer is an automatic, shared pointer in C++. There are not so much Qt examples and demos with QSharedPointer because of the general concept for memory management in Qt using parent–child hierarchy of QObject. The examples on Wikipedia makes no sense to me. For example, if %m is the largest unit it might become larger than 59 in order to consume larger time values. The example below illustrates that it works in both single- and multi-threaded cases, and then reproduces. It behaves exactly. Add a comment. It is similar to std::shared_ptr in C++. C++ (Cpp) QSharedPointer::StopTimer - 1 examples found. If a ptr2's. If you want to actually delete a mutex, you have to remove it from the mutexes mapping. Passing data through threads is a common task in multi-thread programming. QSharedPointer. As reference the example tested on cross environment using GDB:zar. . The lifetime of an object begins after its constructor completes successfully. behaves exactly like a normal pointer for normal purposes, including respect for constness. It can deallocate the underlying implementation detail - the shared reference object, but that doesn't affect anything really that the user cares about; those objects are deallocated only when the. If I have to share this instance in C++, I'll use QSharedPointer or std::shared_ptr. You might be tempted to use QSharedPointer in this case and it would work, but remember that QSharedPointer, just like std::shared_ptr, is a lot heavier construct, as sharing in a multi-threaded world is a "far from 0" overhead thing. You can rate examples to help us improve the quality of. You can use this constructor with any QObject, even if they were not created with QSharedPointer. You can rate examples to help us improve the quality of. If a new note is created, its reference is appended to the list: void Traymenu::newNote () { QSharedPointer<Note> note (new Note (this)); m_noteList << note; } For each Note-element, whichs pointers are in m_noteList, I want to get its title and. Good day QT'ers, wondering if there's a better way to remove a QSharedPointer from a QList loaded with them. But, it all depends on your use case. In Qt we also have QSharedPointer and QSharedPointer<T>::create(. In this example, the source object is a simple binary switch that toggles its state based on a timer. QSharedPointer는 C++의 자동 공유 포인터입니다. C++ (Cpp) QSharedPointer::Count - 2 examples found. 5. The d pointer points to an object of this type. 이는 불변성에 대한 존중을 포함하여 일반적인 목적을 위한 일반 포인터와 똑같이 동작합니다. In the example above, the template specialization for the clone() function calls the EmployeeData::clone() virtual function. To complicate things, debugging reports had absolutely random pattern as well. Neither of your approaches is thread-safe. Having said that, without a perfect forwarding, using this function may be inefficient. If the receiver needs a reference of the sender object, it should retain it in a smart pointer. The application is working as expected (creating and destroying the objects). Member Function Documentation QWeakPointer:: QWeakPointer (const QSharedPointer < T > &other)QSharedPointer: pointer 0x2384d70 already has reference counting Which at the very least gives us a basic idea that there is something wrong, and it involves a QSharedPointer. If used in this way, you can pass around these references and use them like pointers, and. : new MyGizmo. 1011. I also want to keep track of some of the objects with QSharedPointer instances. . Instead, the functions std::static_pointer_cast, std::const_pointer_cast, std::dynamic_pointer_cast and std::reinterpret_pointer_cast. The QSharedPointer is an automatic, shared pointer in C++. The whole point of this function is to allocate the reference count near the object instance in memory, so you have to let it do the allocation. Program gets memory overflow during cycled execution of code part, where large memory is allocated, controlled by QSharedPointers. 2) Objects created in C++ owned via the QSharedPointer system, e. const QSharedPointer< T > &. If somehow the object/container survives so does the smart pointer and the allocated memory. When removeData() returns, any further attempts to reference the sender is undefined behavior. I see that QSharedPointer keeps my data valid if the acquisition threads stop during data is processing. Smart pointers with PythonQt. BTW: I know that std::unique_ptr does not do the same as QSharedPointer, because the latter does reference counting. It behaves exactly like a normal pointer for normal purposes, including respect for constness. QSharedPointer holds a shared pointer by means of an external reference count (i. It behaves exactly like a normal pointer for normal purposes, including respect for constness. QSharedPointer의 주요 기능 중 하나는 스레드로부터 안전하다는 것입니다. Several shared_ptr objects may own the same object. QSharedPointer 是一个 共享指针 ，它与 QScopedPointer 一样包装了new操作符在堆上分配的动态对象，但它实现的是引用计数型的智能指针 ，也就是说，与QScopedPointer不同的是，QSharedPointer可以被自由地拷贝和赋值，在任意的地方共享它，所以QSharedPointer也可以用作容器. 1. Share. The QSharedPointer class holds a strong reference to a shared pointer. You can also use a data stream to read/write raw unencoded binary data. However, when I try to debug using GDB, the debugger receives segmentation faults. QWeakPointer also provides the QWeakPointer::data () method that returns the tracked pointer without ensuring that it remains valid. one pointer (for example, QSharedPointer). The problem is that this code is creating a QSharedPointer from a raw pointer, which implies ownership of the object pointed to. AnotherObject * something;The c++ (cpp) qsharedpointer example is extracted from the most popular open source projects, you can refer to the following example for usage. These are the top rated real world C++ (Cpp) examples of QSharedPointer::at extracted from open source projects. 6. The item object can be destroyed by QSharedPointer destructor, so QChache will have invalid pointer. The problem boiled down to unexpected crashes occurring on random basis. See Customizing QFrame for an example. As reference the example tested on cross environment using GDB:Member Function Documentation QScopedArrayPointer:: QScopedArrayPointer Constructs a QScopedArrayPointer instance. For example, you can use isEmpty() to test whether the queue is empty, and you can traverse a QQueue using QList's iterator classes (for example, QListIterator). Adding a Q_DECLARE_METATYPE () makes the type known to all template based functions, including QVariant. Examples at hotexamples. // OK QSharedPointer < QObject > object3(new QObject); // OK} Using a Mutex to Protect the Integrity of Data. The example will output 1, 2, 3 in that order. Frequently Used Methods. Commented defines are for "not compiling" parts. The shared pointer will automatically destroy its contents only when there are no shared pointers referencing the object originally created for the shared pointer. This maintains a standard interface across Qt classes. The base class tick generator used by QCPAxis to create tick positions and tick labels. Both examples will crash when the first destructor is called. You can rate examples to help us improve the quality of. QPointer:: QPointer () Constructs a guarded pointer with value nullptr. . Here is an example: @ // sender class class A : public QObject {Q_OBJECT public: void test() {QSharedPointer<Data> dataPtr = QSharePointer<Data>(new Data());. The same is for tokencount == 1. A base class that allows obtaining a QSharedPointer for an object already managed by a shared pointer. qRegisterMetaType< QSharedPointer<TestClass> >("SharedTestClass"); in main() not as a global variable. However, upon deleting. As reference the example tested on cross environment using GDB:I'm trying to use QSharedPointer to define an object that will be created in a thread that will emit a signal to another thread. The QCPGraphDataContainer is an abstract data container of QCPGraphData object, one of which will be created for each data point that we parse. ©2023 The Qt Company Ltd. In short - an atomic operation is one that is so "small" (hence the name) that it cannot be interrupted (for example by another thread) and therefore is thread-safe. Most of the time it will just work in Qt because most of the time Qt objects have a parent which will handle deletion of children when destroyed. It is non-owning. staticCast<Switch> (); Both versions are basically equivalent to doing static_cast on raw pointers. Here is a minimal example: #include <QSharedPointer> struct A {}; int main(int argc, char *argv[]) { auto ca = QSharedPointer<const A>::create(); return 0; } Here is one file (not minimal) example but with few working cases, 2 not working and a debug. @Yakk: Thanks for that, I've updated my answer to reflect your point. QSharedPointer:: objectCast() works reliably across DLL boundaries, but QSharedPointer:: dynamicCast() and std::dynamic_pointer_cast() don’t. h: > > // ### Qt6: Using a private here has high impact on runtime > // on users such as QFileInfo. QSharedPointer will delete the pointer it is holding when it goes. 5. Actually, it does so in examples setting custom deleter to Object::deleteLater . Guarded pointers are useful whenever you need to store a pointer. io First of all, could anyone please give me an example where you would ACTUALLY use shared pointers. The reference count is printed to the console using the use_count() method. These are the top rated real world C++ (Cpp) examples of QSharedPointer::GetFormulaRadius extracted from open source projects. QScopedPointer is a small utility class that heavily simplifies this by assigning stack-based memory ownership to heap allocations, more generally called resource acquisition is. It behaves exactly like a normal pointer for normal purposes, including respect for constness. Qt로 프로그래밍할 때 메모리 관리 문제 (메모리 관리 불량으로 인한 메모리 누수 및 버그. The lifetime of an object begins after its constructor completes successfully. For example, if you need to find all unique shared_ptr from a vector, you need such a predicate. qRegisterMetaType< QSharedPointer<TestClass> >("SharedTestClass"); in main() not as a global variable. data (); } When you delete the pointed-to object, data () will be null. C++ (Cpp) QSharedPointer::GetFormulaRadius - 2 examples found. Call doc:QSharedPointer :: data () to get a pointer to the referenced class; Make sure the QML engine doesn't assume ownership: doc:QDeclarativeEngine :: setObjectOwnership (P). Based on my research, I believe QSharedPointer is the correct answer. See also append() and insert(). The Q_DECLARE_METATYPE macro is necessary in both cases. The reference count for the new pointer is also printed. C++ (Cpp) QSharedPointer::GetP2 - 2 examples found. In general, it breaks the concept of having a shared pointer at all. Scale the images. For example, using data() for QObject::connect() would be save, but. It behaves exactly like a normal pointer for normal purposes, including respect for constness. It adds only one member to its parent, which is of type T (the actual type, not a pointer to it). As a iOS developer, I use a kind of smart pointers with reference counting implemented in NSObject whereby Im able to retain and release pointers when needed. The QSharedPointer is an automatic, shared pointer in C++. When the code block containing ptr2 ends, its reference. keyToAscii (key). C++ (Cpp) QSharedPointer::clone - 13 examples found. You can rate examples to help us improve the quality of examples. It. It behaves exactly like a normal pointer for normal purposes, including respect for constness. foo(QSharedPointer<QPushButton>(new QPushButton("Cancel", this)), MayThrow()); That is, if the compiler first executes the new QPushButton("Cancel", this) expression, and then calls the MayThrow() function before calling the constructor of QSharedPointer , you may leak memory if the MayThrow() function throws an exception. 212: 213: This class is never instantiated directly: the constructors and: 214 In the example above, the template specialization for the clone() function calls the EmployeeData::clone() virtual function. QSharedPointer<MyClass> mc (new MyClass ()); mc->testSharedThis ();The code the compiler generates for QScopedPointer is the same as when writing it manually. C++ Class Qt 스마트 포인터 (QSharedPointer, QScopedPointer, QPointer) 스마트 포인터는 C++표준 포인터의 모든 기능을 가지고 있으며 자동 가비지 컬렉션 기능을 제공하는 클래스이다. This looks to me as a Bug in Qt but I couldn't find an issue and I am not sure if some compiler settings are wrong. QSharedPointer:: objectCast() works reliably across DLL boundaries, but QSharedPointer:: dynamicCast() and std::dynamic_pointer_cast() don’t. The code below won't leak memory and doesn't invoke any undefined behavior. QSharedPointer guarantees that the object isn't deleted, so if you obtain a non-null object, you may use the pointer. It behaves exactly like a normal pointer for normal purposes, including respect for constness. The requester class should also be in charge of managing the memory of the pointer it created. Qt doesn't have garbage collection. new children are appended at. Good Morning everyone, I am using QSharedPointer with my classes derived from QObject. 1 Answer. If you want a container class that provides a fast prepend() function, use QList or QLinkedList instead. It has all the features you may want in a modern pointer class: it is polymorphic, it supports static, const, and dynamic casts, it implements atomic reference-counting and thread-safe semantics, it supports. The problem of owner ship of the memory is avoided. The QSharedPointer is an automatic, shared pointer in C++. If you need a QSharedPointer, don't set. In your case, you are letting QMainWindow to delete cV when user closes it. List of all members, including inherited members; Public FunctionsA "null" QSharedPointer wraps a T* t where t equals 0/NULL/nullptr. QSharedPointer works with forward declarations, so I'd guess you're using it incorrectly; consider giving a minimal example that can be compiled (and more importantly doesn't require us to guess about the types). In a related question: Waiting slots to be executed before quitting. Usually one puts this (note that the typedefed name is used as string argument): qRegisterMetaType< QSharedPointer<TestClass> > ( "SharedTestClass" );My intention was, since I had to store the actual data in another QSharedPointer, to make a connect on that shared pointer that tells the other widget. Before drawing you would create a local QSharedPointer<MyClass> in the drawing function and check if it is valid. Maybe it is a proper thing to add some C++14-style wrapper for creating QObjects like this: @ namespace Qt. or if you already have a reference to a pointer, then use the reset () method as follows: Qsharedfoo. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. MyClass * myIns = new MyClass (); QSharedPointer<MyClass> asp ( myIns); QVariant aVariant = QVariant::fromValue( asp); To copy to clipboard, switch view to plain text mode. The temporary instance of the shared pointer allocated on the heap in answer1 will be deallocated by its shared pointer. That means they should have a default constructor, a copy constructor, and an assignment operator. I know the QSharedPointer object gets deleted once the function goes out of scope in the test function() which would decrement the reference count, but would the. Several GBs of memory are en vogue today, but ultimately you can drain any big pond (as long as you do not call it ocean) ;-) [/. h","contentType":"file. 04 and in my application I need to use QSharedPointer together with the appropriate dynamic_cast (object_cast) conversions at runtime. An. QSharedPointer IF you using a pointer and start giving pointer to other functions and you are passing your pointer all over. The first MyClass object pointer 0x13defe0 is assigned to the QPointer instance, the second one (0x110f780) to QSharedPointer instance.