TRUE - Param2 contains absolute coordinates.
FALSE - Param2 contains relative coordinates.

Pointer to a COORD structure containing the new coordinates of the upper left corner of the dialog window.

The COORDstructure containing the current coordinates of the upper left corner of the dialog window.

In order to center the dialog window on the screen fill the COORD structure with -1 values and set Param1 = TRUE.

// center the dialog
COORD c={-1,-1};
Info.SendDlgMessage(hDlg,DM_MOVEDIALOG,TRUE,(LONG_PTR)&c);

// move the dialog to the top left corner of the screen with coordinates 1,1
COORD c={1,1};
Info.SendDlgMessage(hDlg,DM_MOVEDIALOG,TRUE,(LONG_PTR)&c);

// move the dialog by 2 positions to the right
COORD c={2,0};
Info.SendDlgMessage(hDlg,DM_MOVEDIALOG,FALSE,(LONG_PTR)&c);