When data moves from IDL to a COM object and back, IDL handles conversion of variable data types automatically. The data type mappings are shown below.
|
COM Type
|
IDL Type
|
|
BOOL (VT_BOOL)
|
Byte (true =1, false=0)
|
|
ERROR (VT_ERROR)
|
Long |
|
CY (VT_CY) |
Double (see note below)
|
|
DATE (VT_DATE) |
Double |
|
I1 (VT_I1) |
Byte |
|
INT (VT_INT) |
Long |
|
UINT (VT_UINT) |
Unsigned Long |
|
VT_USERDEFINED |
The IDL type is passed through
|
|
VT_UI1 |
Byte |
|
VT_I2 |
Integer |
|
VT_UI2 |
Unsigned integer
|
|
VT_ERROR |
Long |
|
VT_I4 |
Long |
|
VT_UI4 |
Unsigned Long |
|
VT_I8 |
Long64 |
|
VT_UI8 |
Unsigned Long 64
|
|
VT_R4 |
Float |
|
VT_BSTR |
String |
|
VT_R8 |
Double |
|
VT_DISPATCH |
IDLcomIDispatch |
|
VT_UNKNOWN |
IDLcomIDispatch |
Note on the COM CY Data Type
The COM CY data type is a scaled 64-bit integer, supporting exactly four digits to the right of the decimal point. To provide an easy-to-use interface, IDL automatically scales the integer as part of the data conversion that takes place between COM and IDL, allowing the IDL user to treat the number as a double-precision floating-point value. When the value is passed back to the COM object, it will be truncated if there are more than four significant digits to the right of the decimal point.
For example, the IDL double-precision value 234.56789 would be passed to the COM object as 234.5678.