C++ auto_ptr and shared_ptr

std::auto_ptr

Good article on why and how to use it Another good article on when and how to use it

{
  auto_ptr<T> ptr( new T );
  ...
} // when ptr goes out of scope it deletes the underlying object!

• auto_ptr employs the "exclusive ownership" model. This means that you can't bind more than one auto_ptr object to the same resource.
• Be careful when passing as a parameter to a method by value because on returning the pointer will point to nothing. The copy in the method will destroy the pointer when the method ends, so pass it by reference.
• Also because of this do not use it with template libraries!

std::tr1::shared_ptr

• Unlike auto_ptr, shared_ptr uses reference counting so multiple "shared_ptr"s can point to the same resource.
• Destructor decrement the reference count. When it reaches zero the resource is "delete"d.
• Can have a user defined deleter, so shared_ptr need not necessarily hold a "pointer to something" type resource, it could be a file handle, etc. Define a "delete" function to delete the custom resource
• Be careful of cyclic references, the objects will not be able to delete one another