public static RECT Union( 
   RECT rect1,
   RECT rect2
)

Parameters

rect1

rect2

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

RECT Structure
RECT Members