lpClassName

lpClassName is a parameter used in certain Windows API functions, specifically those related to window class registration and creation. The 'lp' prefix typically stands for "long pointer," indicating a pointer to a string. The 'ClassName' part signifies that the string being pointed to is the name of a window class.

Window classes are fundamental to the Windows graphical user interface. They define the appearance, behavior, and window procedure (callback function) for a type of window. When an application wants to create a window, it needs to specify the class of that window. The lpClassName parameter serves this purpose, allowing developers to identify the pre-registered window class that the new window should be based upon.

For instance, the CreateWindowEx function uses lpClassName to specify the class of the window to be created. If an application registers a custom window class using RegisterClassEx, it assigns a unique name to that class. This name is then passed as lpClassName when creating windows of that custom type. If lpClassName is NULL or an empty string, the system uses a default window class. The case of the class name is generally not significant.