What does ->std::ostream& mean?

Question

Here is the part of codes that i cannot understand.This is a func definition.

using sPtr = std::shared_ptr < std::vector<int> >;
auto print(sPtr vec) ->std::ostream&;

what does it mean by -> std::ostream& ? Is it necessary or not ? In my opinion,

void print (sPtr vec) ;

I am learning CPP5 ch12 now, and the code is from github Mooophy/Cpp-Primer; Thanks everyone's advice.

Answer 1

print is a function taking a sPtr as an input and returning an std::ostream& . The syntax being used was introduced in C++11, and it's called "trailing return type" .

The declaration of print can be rewritten as follows:

std::ostream& print(sPtr vec);