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std::allocate_shared

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< cpp‎ | memory‎ | shared ptr
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Defined in header <memory>
template< class T, class Alloc, class... Args >
shared_ptr<T> allocate_shared( const Alloc& alloc, Args... args );

Constructs an object of type T and wraps it in a std::shared_ptr using args as the parameter list for the constructor of T.

All memory allocation is done using a copy of alloc, which satisfies the Allocator requirements. The copy constructor and the destructor of Alloc must not throw exceptions.

Contents

[edit] Parameters

alloc - The Allocator to use.
args... - list of arguments with which an instance of T will be constructed.

[edit] Return value

std::shared_ptr of an instance of type T.

[edit] Exceptions

Can throw the exceptions thrown from Alloc::allocate() or from the constructor of T. If an exception is thrown, this function has no effect.

[edit] Notes

This function typically allocates memory for the T object and for the shared_ptr's control block with a single memory allocation (it is a non-binding requirement in the Standard). In contrast, the declaration std::shared_ptr<T> p(new T(Args...)) performs at least two memory allocations, which may incur unnecessary overhead.

A copy of alloc is stored as part of the control block so that it can be used to deallocate it once both shared and weak reference counts reach zero.

[edit] See also

constructs new shared_ptr
(public member function) [edit]
creates a shared pointer that manages a new object
(function template) [edit]