C#访问非托管内存

Point p;
// Initialize unmanged memory to hold the struct.
IntPtr pnt = Marshal.AllocHGlobal(Marshal.SizeOf(p));
// Copy the struct to unmanaged memory.
Marshal.StructureToPtr(p, pnt, false);

// Create another point.
Point anotherP;

// Set this Point to the value of the 
// Point in unmanaged memory. 
anotherP = (Point)Marshal.PtrToStructure(pnt, typeof(Point));
Marshal.FreeHGlobal(pnt);

IntPtr lpFileName;
string filename = Marshal.PtrToStringUni(lpFileName);
lpFileName = Marshal.StringToHGlobalUni(filename);