smart_pointers.md

智能指针

In modern C++ programming, the Standard Library includes smart pointers, which are used to help ensure that programs are free of memory and resource leaks and are exception-safe.
https://docs.microsoft.com/en-us/cpp/cpp/smart-pointers-modern-cpp?view=msvc-170

C++ Standard Library smart pointers

Use these smart pointers as a first choice for encapsulating pointers to plain old C++ objects (POCO).

• unique_ptr
  • Allows exactly one owner of the underlying pointer. Use as the default choice for POCO unless you know for certain that you require a shared_ptr.
  • Can be moved to a new owner, but not copied or shared.
  • Replaces auto_ptr, which is deprecated. Compare to boost::scoped_ptr. unique_ptr is small and efficient; the size is one pointer and it supports rvalue references for fast insertion and retrieval from C++ Standard Library collections.
  • Header file: <memory>.
  • How to: Create and Use unique_ptr Instances
• shared_ptr
  • Reference-counted smart pointer. Use when you want to assign one raw pointer to multiple owners, for example, when you return a copy of a pointer from a container but want to keep the original.
  • The raw pointer is not deleted until all shared_ptr owners have gone out of scope or have otherwise given up ownership.
  • The size is two pointers; one for the object and one for the shared control block that contains the reference count.
  • Header file: <memory>.
  • How to: Create and Use shared_ptr Instances
• weak_ptr
  • Special-case smart pointer for use in conjunction with shared_ptr. A weak_ptr provides access to an object that is owned by one or more shared_ptr instances, but does not participate in reference counting.
  • Use when you want to observe an object, but do not require it to remain alive. Required in some cases to break circular references between shared_ptr instances.
  • Header file: .
  • How to: Create and Use weak_ptr Instances