为什么std :: shared_ptr提供运算符<<？

Question

std::shared_ptr provides operator<< which just writes out its address. There is no operator>> and only the address without the content is recorded. I am wondering in which cases it is useful.

Answer 1

Because it is a potentially useful thing that << does on a raw pointer. It is safe, and it is what raw pointers do, and shared_ptr is supposed to be used to replace raw pointers in some situations.

In comparsion, >> would very rarely make sense. Unlike a raw pointer, storing a pointer value in a shared pointer takes ownership of it.

I can some_stream >> raw_ptr and unless I do something with ptr nothing goes wrong; a bit strange, but nothing immediately breaks.

Doing the same to shared_ptr would only be safe in extremely esoteric situations. In those situations, having to take a step where we first populate a raw pointer then load it into the shared pointer doesn't seem like an overly burdensome requirement.