src_corelib_tools_qsharedpointer.cpp

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// Copyright (C) 2018 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
    class Y: public QEnableSharedFromThis<Y>
    {
    public:
        QSharedPointer<Y> f()
        {
            return sharedFromThis();
        }
    };
 
    int main()
    {
        QSharedPointer<Y> p(new Y());
        QSharedPointer<Y> y = p->f();
        Q_ASSERT(p == y); // p and q must share ownership
    }
 
    class ScriptInterface : public QObject
    {
        Q_OBJECT
 
        // ...
 
    public slots:
        void slotCalledByScript(Y *managedBySharedPointer)
        {
            QSharedPointer<Y> yPtr = managedBySharedPointer->sharedFromThis();
            // Some other code unrelated to scripts that expects a QSharedPointer<Y> ...
        }
    };
 
    static void doDeleteLater(MyObject *obj)
    {
        obj->deleteLater();
    }
 
    void otherFunction()
    {
        QSharedPointer<MyObject> obj =
            QSharedPointer<MyObject>(new MyObject, doDeleteLater);
 
        // continue using obj
        obj.clear();    // calls obj->deleteLater();
    }
 
    QSharedPointer<MyObject> obj =
        QSharedPointer<MyObject>(new MyObject, &QObject::deleteLater);
 
    if (sharedptr) { ... }
 
    if (!sharedptr) { ... }
 
    QSharedPointer<T> other(t); this->swap(other);
 
    QSharedPointer<T> other(t, deleter); this->swap(other);
 
    if (weakref) { ... }
 
    if (!weakref) { ... }
 
    qDebug("Tracking %p", weakref.data());
 
    // this pointer cannot be used in another thread
    // so other threads cannot delete it
    QWeakPointer<int> weakref = obtainReference();
 
    Object *obj = weakref.data();
    if (obj) {
        // if the pointer wasn't deleted yet, we know it can't get
        // deleted by our own code here nor the functions we call
        otherFunction(obj);
    }
 
    QWeakPointer<int> weakref;
 
    // ...
 
    QSharedPointer<int> strong = weakref.toStrongRef();
    if (strong)
        qDebug() << "The value is:" << *strong;
    else
        qDebug() << "The value has already been deleted";