Storing and using Windows Handle ( WId ) in registry

I wish to store the Window handle of a running instance of an application in the registry, the WId of a widget. I need this to ensure that if another application starts, it can check the registry to know whom it is supposed to send a message to, using sendMessage() windows API. How do I achieve this? The type of a Windows handle , HWND, of which WId is a typedef..is a void pointer. How do I store information of this type in a registry setting, and then retrieve to use it again? Please help me with this. I’ll be obliged. Thanks.