std::allocate_shared

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.

Parameters

Return value

std::shared_ptr of an instance of type T.

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.

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.

See also