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It is created as a copy of a shared_ptr. The existence or destruction of weak_ptr copies of a shared_ptr have no effect on the shared_ptr or its other copies. After all copies of a shared_ptr have been destroyed, all weak_ptr copies become empty.
For this purpose, the C++11 standard library defines the smart pointer classes std::unique_ptr for single-owned objects and std::shared_ptr for objects with shared ownership. Similar classes are also available through std::auto_ptr in C++98, and boost::shared_ptr in the Boost libraries. Also, messages can be sent to network resources using RAII.
The C++11 standard made auto_ptr deprecated, replacing it with the unique_ptr class template. [3] [4] auto_ptr was fully removed in C++17. [5] For shared ownership, the shared_ptr template class can be used. shared_ptr was defined in C++11 and is also available in the Boost library for use with previous C++ versions. [6]
To illustrate the issue, consider that an std::vector<T> is, internally, a wrapper around a C-style array with a defined size. If an std::vector<T> temporary is created or returned from a function, it can be stored only by creating a new std::vector<T> and copying all the rvalue's data into it. Then the temporary and all its memory is destroyed.
std::make_shared and std::allocate_shared for arrays; Changes applied to the C++20 working draft in the fall meeting in November 2017 (Albuquerque) include: [86] [87] three-way comparison using the "spaceship operator", operator <=> initialization of an additional variable within a range-based for statement; lambdas in unevaluated contexts
std::make_unique can be used like std::make_shared for std::unique_ptr objects. [7] std::integral_constant gained an operator() overload to return the constant value. [16] The class template std::integer_sequence and related alias templates were added for representing compile-time integer sequences, such as the indices of elements in a ...
Objects that are dynamically allocated but not intended to be shared can have their lifetime automatically managed using a std::unique_ptr. In addition, C++11's move semantics further reduce the extent to which reference counts need to be modified by removing the deep copy normally used when a function returns an object, as it allows for a ...
Function composition is also allowed. This is a generalized version of the standard std::bind1st and std::bind2nd bind functions. The feature is based on Boost Bind library. [4] Function return types (result_of) – determines the type of a call expression. Member functions (mem_fn) – enhancement to the standard std::mem_fun and std::mem_fun_ref.