The WM_COPYDATA message is sent when an application passes data to another application.
WM_COPYDATA
wParam = (WPARAM) (HWND) hwnd; // handle of sending window
lParam = (LPARAM) (PCOPYDATASTRUCT) pcds; // pointer to structure with data
If the receiving application processes this message, it should return TRUE; otherwise, it should return FALSE.
An application must use the SendMessage function to send this message, not the PostMessage function.
The data being passed must not contain pointers or other references to objects not accessible to the application receiving the data.
While this message is being sent, the referenced data must not be changed by another thread of the sending process.
The receiving application should consider the data read-only. The pcds parameter is valid only during the processing of the message. The receiving application should not free the memory referenced by pcds. If the receiving application must access the data after SendMessage returns, it must copy the data into a local buffer.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Interprocess Communications Overview, Interprocess Communications Messages, PostMessage, SendMessage, COPYDATASTRUCT