Scalar Fields

Scalar fields are essentially the familiar base types of C and C++. We have chosen to use the Windows™ names for these types because they are independent of machine word size. So, for example, there are BOOLFields to represent boolean values, and WORDFields to represent unsigned 16-bit integers. These types are straightforward to use, and there are very many example in the system (e.g. LOGBRUSH). The complete set of ScalarFields defined at the time of writing is listed in the following table:

ExternalField Class	C type(s)	Description
BOOLField	BOOL	32-bit integer interpreted as TRUE if non-zero
BYTEField	BYTE	Unsigned 8-bit integer
DOUBLEField	double	64-bit double precision IEEE Float
DWORDField	DWORD, UINT	32-bit unsigned integer
HANDLEField	HANDLE, HWND, etc	32-bit opaque handle types, e.g.
LPVOIDField	void*	Generic pointer/address field (see Address Fields)
FLOATField	float	32-bit single precision IEEE Float
QWORDField	unsigned __int64	Unsigned 64-bit integer
SBYTEField	SBYTE	Signed 8-bit integer
SDWORDField	SDWORD, int	32-bit signed integer
SQWORDField	__int64	64-bit signed integer
SWORDField	SWORD	16-bit signed integer
WORDField	WORD	16-bit unsigned integer

Address Fields

The most quirky scalar field type is LPVOIDField, which is used when one wants to access the pointers stored in structures as pointers, rather than the object pointed at by the pointer! Typically one does not want to worry about the indirection, and so one should employ pointer fields that automatically de-reference the pointer so that one can work with objects instead of addresses.

An example can be found in the EDITSTREAM structure used with the Rich Edit control, which stores down a function pointer (into which we store an ExternalCallback):

defineFields

"Define the fields of the Win32 EDITSTREAM structure.

EDITSTREAM compileDefinition

typedef struct _editstream {

DWORD dwCookie;

DWORD dwError;

EDITSTREAMCALLBACK pfnCallback;

} EDITSTREAM;"

self

defineField: #dwCookie type: DWORDField writeOnly;

defineField: #dwError type: DWORDField filler;

defineField: #pfnCallback type: LPVOIDField writeOnly