what's the point of std::unique_ptr::get

Question

Doesn't std::unique_ptr::get defeat the purpose of having a unique_ptr in the first place? I would have expected this function to change its state so it holds no more pointer. Is there an actual useful use of std::unique_ptr::get?

Solution 1

std::unique_ptr provides unique ownership semantics safely. However that doesn't rule out the need for non-owning pointers. std::shared_ptr has a non-owning counterpart, std::weak_ptr. Raw pointers operate as std::unique_ptr's non-owning counterpart.

Solution 2

You use it every time you need to pass raw pointer to, say, a C function:

std::unique_ptr<char[]> buffer( new char[1024] );
// ... fill the buffer
int rc = ::write( fd, buffer.get(), len );

Solution 3

The rule I tend to follow is this: if the callee isn't mucking with lifetime/ownership, do not pass it a smart pointer; rather, pass in a raw C++ reference (preferred) or raw pointer. I find it far cleaner and more flexible to separate the concern of ownership from usage.

Solution 4

When your hands are tied and you do need to pass a pointer to something, p.get() reads better than &*p.

There is a function that changes the state so the unique_ptr doesn't hold a pointer anymore, and that one is named release. This is mostly useful to transfer ownership to other smart pointers that don't provide direct construction from a unique_ptr. Any other use risks leaking the resource.

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