COM Type-Cast Conversions

COM Type-Cast Conversions

If any of variable data type declaration suffixes is used or if missing and variable's type is found , COM parser will automatically convert VARIANTS to and from that data type.

Variable data type declaration suffix

The data type of a variable can be indicated by a data type declaration suffix (%, !, # or $) appended to the variable name.

The % in
```
  
DIM A%
```
indicates that A is an integer variable.
The ! in
```
  
DIM B!
```
indicates that B is a single precision float variable.
The # in
```
  
DIM C#
```
indicates that C is a double precision float variable.
The $ in
```
  
DIM D$
```
indicates that D is string variable.

Samples:

' parser will pass string variable and automatically convert to BSTR
cdonts.from = D$

' Parser will pass Integer variable.
app.activeworkbook.cells(1,3).value = A%

' Parser will pass float variable.
app.activeworkbook.cells(1,3).value = B!

If no type is specified, an attempt is made to find the variable's type and, if found, it is used. Otherwise, the BCX COM parser will pass a long as the default data type.

The BCX COM parser uses similar syntax for type-casting as the C language. The only difference is that all casts are always from and to the VARIANT data type and casting may occur to and from one of the constants defined in table below.

' Parser will convert integer A% to double precision float.
app.activeworkbook.cells(1,3).value = (VT_R8) A%

' result of GetCom method will be converted to float.
B! = (VT_R4) app.activeworkbook.cells(4,3).value

If the return type is not known then you may use a varible of type VARIANT and check the .vt for what type is returned. For example,

DIM vRet AS VARIANT
vRet = app.activeworkbook.cells(1,3).value

IF vRet.vt = VT_R8 THEN
  ' do something if it's a double
  ' Access val with vRet.dblval
 ELSEIF vRet.vt = VT_BSTR
  ' do something if it's a BSTR (note: BSTR is a wide strings)
 ' Access val with vRet.bstrVal
END IF

👉 some COM calls return different types.

List of available conversion definitions:

Valid casts (VT_...)	C/C++ equivalent	member
VT_NONE	void	void
VT_UI1	unsigned char	bVal
VT_UI1REF	unsigned char*	by reference
VT_I2	SHORT	iVal
VT_I2REF	SHORT*	by reference
VT_I4	long	lVal
VT_I4REF	long*	by reference
VT_R4	float	fltVal
VT_R4REF	float*	by reference
VT_R8	double	dblVal
VT_R8REF	double*	by reference
VT_UI8	unsigned __int64	uhVal
VT_UI8REF	unsigned __int64*	by reference
VT_I1	char	bVal
VT_I1REF	char*	by reference
VT_UI2	USHORT	uiVal
VT_UI2REF	USHORT*	by reference
VT_UI4	ULONG	ulVal
VT_UI4REF	ULONG*	by reference
VT_INT	int	lVal
VT_INTREF	int*	by reference
VT_UINT	UINT	ulVal
VT_UINTREF	UINT*	by reference
VT_CY	CY	cyVal
VT_CYREF	CY*	by reference
VT_DATE	DATE	date
VT_DATEREF	DATE*	by reference
VT_BSTR	BSTR	bstrVal
VT_BSTRREF	BSTR*	by reference
VT_DISPATCH	IDispatch*	pdispVal
VT_DISPATCHREF	IDispatch**	by reference
VT_ERROR	SCODE	scode
VT_ERRORREF	SCODE*	by reference
VT_BOOL	VARIANT_BOOL	boolVal
VT_BOOLREF	VARIANT_BOOL	by reference
VT_UNKNOWN	IUnknown*	punkVal
VT_UNKNOWNREF	IUnknown**	by reference
VT_VARIANTREF	VARIANT*	by reference
VT_ARRAY	SAFEARRAY	parray
VT_ARRAYREF	SAFEARRAY*	by reference
VT_DECIMAL	DECIMAL	decVal
VT_DECIMALREF	DECIMAL*	by reference