cpp/experimental/set default resource

If is not null, sets the default memory resource pointer to ; otherwise, sets the default memory resource pointer to.

The default memory resource pointer is used by certain facilities when an explicit memory resource is not supplied. The initial default memory resource pointer is the return value of.

This function is thread-safe. Every call to synchronizes with (see std) the subsequent  and get_default_resource calls.

Return value
Returns the previous value of the default memory resource pointer.