Instance Handle

Every window class requires an instance handle to identify the application or DLL that registered the class. As a multitasking system, Windows lets several applications or DLLs run at the same time, so it requires instance handles to keep track of all of them. Windows assigns a handle to each copy of a running application or DLL.

Multiple instances of the same application or DLL all use the same code segment, but each has its own data segment. Windows uses an instance handle to identify the data segment that corresponds to a particular instance of an application or DLL.

Windows passes an instance handle to an application or DLL when the application starts. The application or DLL assigns this instance handle to the class by copying it to the hInstance member of the WNDCLASSEX structure.

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