C++ - passing references to std::shared_ptr or boost::shared_ptr

Question

If I have a function that needs to work with a shared_ptr, wouldn\'t it be more efficient to pass it a reference to it (so to avoid copying the shared_ptr

Answer 1

struct A {
  shared_ptr msg;
  shared_ptr * ptr_msg;
}

1. pass by value:

   void set(shared_ptr msg) {
     this->msg = msg; /// create a new shared_ptr, reference count will be added;
   } /// out of method, new created shared_ptr will be deleted, of course, reference count also be reduced;
   

2. pass by reference:

   void set(shared_ptr& msg) {
    this->msg = msg; /// reference count will be added, because reference is just an alias.
    }
   

3. pass by pointer:

   void set(shared_ptr* msg) {
     this->ptr_msg = msg; /// reference count will not be added;
   }