WMDROPFILES

WM_DROPFILES is a Windows message sent to a window when the user drops one or more files or folders onto it using the Shell drag‑and‑drop feature. The receiving window must be registered to accept drops by calling DragAcceptFiles with TRUE. When files are dropped, the system posts WM_DROPFILES to the window procedure with lParam containing an HDROP handle that identifies the dropped items.

To process the drop, the application uses the DragQueryFile API. First, obtain the number of dropped files by calling DragQueryFile with nFile set to 0xFFFFFFFF. Then iterate from 0 to count-1 and call DragQueryFile with the index to retrieve each file path. The retrieved paths can be stored, displayed, or opened as needed. After all file paths are processed, release the HDROP handle by calling DragFinish.

Notes and variants: The correct Windows message name is WM_DROPFILES; some references spell it as WMDROPFILES. The DragQueryFile API has Unicode and ANSI variants (DragQueryFileW and DragQueryFileA); typically a macro maps to the appropriate version based on the build. Applications often handle multiple files in one drop and must manage buffer sizes to accommodate long paths.

Security and behavior considerations include validating the received paths, handling potential long file names, and ensuring the app does not assume any particular action. The message provides paths to files on the client machine, but it is the responsibility of the application to decide how to use or copy those files.