C++11 中的 intrusive_ptr

It does have std::make_shared which means std::shared_ptr is almost (see note below) as efficient as an intrusive smart pointer, because the reference counts will be stored adjacent in memory to the object itself, improving locality of reference and cache usage. It also provides std::enable_shared_from_this which allows you to retrieve a std::shared_ptr when you only have a built-in pointer to an object owned by a shared_ptr, but that doesn't allow you to manage the object using different smart pointer types.

shared_ptr 期望完全负责管理对象.不同的智能指针类型可能只管理强"引用计数而不是弱"引用计数，这将导致计数不同步并破坏 shared_ptr 的不变量.

shared_ptr expects to be entirely responsible for managing the object. A different smart pointer type might only manage the "strong" refcount and not the "weak" refcount, which would allow the counts to get out of sync and break the invariants of shared_ptr.

注意:使用 make_shared 允许 shared_ptr 几乎 与侵入式指针一样有效.当使用 make_shared 时，对象和引用计数信息可以分配在单个内存块中，但仍然会有两个引用计数(对于强"和弱"计数)侵入式指针不是这种情况，因为它们不支持 weak_ptr.此外，shared_ptr 对象本身总是必须存储两个指针(一个由 shared_ptr::get() 返回，另一个指向控制块"的指针，包含引用计数并知道所拥有对象的动态类型)因此比侵入式指针占用空间更大.

Note: Using make_shared allows shared_ptr to be almost as efficient as an intrusive pointer. The object and the reference counting info can be allocated in a single chunk of memory when make_shared is used, but there will still be two reference counts (for the "strong" and "weak" counts) which isn't the case for intrusive pointers as they don't support a weak_ptr. Also, the shared_ptr object itself always has to store two pointers (the one that will be returned by shared_ptr::get() and another pointer to the "control block" that contains the reference counts and knows the dynamic type of the owned object) so has a larger footprint than an intrusive pointer.

这篇关于C++11 中的 intrusive_ptr的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！