QCache和QSharedPointer [英] QCache and QSharedPointer

问题描述

问题是，我有 QVector 的 QSharedPointer ，我想把它们的一部分 QCache 。如何插入一个共享指针 QCache ？如果我将指针设置为我的缓存但是破坏了 QVector 和共享指针，会发生什么？将内存释放，我的缓存指向无处吗？

The problem is, that I have a QVector of QSharedPointer and I want to put part of them to my QCache. How can I insert a shared pointer to QCache? What happens if I set the pointer to my cache but destroy the QVector and the shared pointer in it? Will the memory be released and my cache points to nowhere?

推荐答案

这是一个错误，如果你只是一个指针指向你的项目 QChache ，同时这样的指针由 QSharedPointer 管理。 item对象可以被 QSharedPointer 析构函数销毁，因此 QChache 将有无效的指针。这是一个通用的问题，你不能有不同的指针的所有者不知道对方。如果你通过 QSharedPointer< Item> 管理指针，那么 QChache 不能直接使用 / code>，它只能与 QSharedPointer< Item> 配合使用，例如：

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. The item object can be destroyed by QSharedPointer destructor, so QChache will have invalid pointer. It is a generic issue that you cannot have different owners of a pointer that do not know each other. If you manage pointers by QSharedPointer<Item> then QChache should not work directly with Item it should work only with QSharedPointer<Item>, for example:

// wrong
QCache<int, Item> cache;
QVector<QSharedPointer<Item> > vec;
Item *item = new Item;
vec.push_back(QSharedPointer<Item>(item));
cache.insert(1, item);
// or
cache.insert(1, vec.at(0).data());

// also wrong
QCache<int, <QSharedPointer<Item> > cache;
vec.push_back(QSharedPointer<Item>(item));
cache.insert(1, new QSharedPointer<Item>(item));
// here two different instances of QSharedPointer are initialized
// by the same pointer 'item'

// correct
QCache<int, <QSharedPointer<Item> > cache;
cache.insert(1, new QSharedPointer<Item>(vec.at(0)));

因此， QCache 应该有自己的副本的动态分配 QSharedPointer 对象和 QSharedPointer 对象应该正确初始化其他 QSharedPointer 已拥有 Item 实例的所有权。

So, QCache should have its own copy of dynamically allocated QSharedPointer object and that QSharedPointer object should be correctly initialized by other QSharedPointer that already has ownership of the Item instance.

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