When to use AddRef?

When to use AddRef?

You use AddRef to stabilize a copy of an interface pointer. It can also be called when the life of a cloned pointer must extend beyond the lifetime of the original pointer.

What is IUnknown interface?

IUnknown is the base interface of every other COM interface. This interface defines three methods: QueryInterface, AddRef, and Release. QueryInterface allows an interface user to ask the object for a pointer to another of its interfaces. AddRef and Release implement reference counting on the interface.

What is the use of IUnknown interface?

Enables clients to get pointers to other interfaces on a given object through the QueryInterface method, and manage the existence of the object through the AddRef and Release methods.

What is QueryInterface?

QueryInterface is a mechanism in COM (microsoft’s Component Object Model) for determining if a known component supports a specific interface. You use the current interface pointer (usually IUnknown), and “query” the interface by passing an interface ID to it.

What is reference count in python?

Reference counting. Reference counting is a simple technique in which objects are deallocated when there is no reference to them in a program. Every variable in Python is a reference (a pointer) to an object and not the actual value itself. A single object can have many references (variable names).

What is AddRef?

AddRef is used to increment the reference count when a new client is acquiring the object. It returns the new reference count. Release is used to decrement the reference count when clients have finished using the object.

What is IDispatch interface?

IDispatch is the interface that exposes the OLE Automation protocol. The Automation (IDispatch) interface allows a client application to find out what properties and methods are supported by an object at run-time, i.e. implements the concept of RTTI.

What is ComPtr?

Microsoft::WRL::ComPtr is a C++ template smart-pointer for COM objects that is used extensively in Windows Runtime (WinRT) C++ programming. It works in Win32 desktop applications as well, and will work on Windows 7. Microsoft::WRL:::ComPtr is in the Windows 8.

What is Refiid?

The riid parameter is the GUID that identifies the interface you are asking for. The data type REFIID is a typedef for const GUID& . Only the interface identifier is necessary. The ppvObject parameter receives a pointer to the interface.

How do I see the reference count in Python?

There are 2 ways to get the reference count of the object:

  1. Using getrefcount from sys module. In Python, by default, variables are passed by reference. Hence, when we run sys.
  2. Using c_long.from_address from ctypes module. In this method, we pass the memory address of the variable. So, ctypes.

Is Python pass by value or reference?

The two most widely known and easy to understand approaches to parameter passing amongst programming languages are pass-by-reference and pass-by-value. Unfortunately, Python is “pass-by-object-reference”, of which it is often said: “Object references are passed by value.”

What is the use of AddRef () and release () in C++?

They are used to track how many references to the object are in use. Calling addref () increments the reference count and release () decrements it. You call addref () to ensure that it knows you are using the object so that it doesn’t destroy it.

What is the internal reference counter of AddRef?

The internal reference counter that AddRef maintains should be a 32-bit unsigned integer. Call this method for every new copy of an interface pointer that you make. For example, if you return a copy of a pointer from a method, then you must call AddRef on that pointer.

How many times do I need to release an AddRef?

The basic rules are: Call Release once for each time you call AddRef on a object. If you created a object instance you also have to release it. Pseudo code for the implementation of a STA interface might look something like this:

How to implement release method of IUnknown COM interface?

Here is a standard (not to say recommended) way of implementing Release method of the IUnknown COM interface (directly taken from MSDN): ULONG CMyMAPIObject::Release() { // Decrement the obje… Stack Overflow About Products For Teams Stack OverflowPublic questions & answers