Type Codes

Every IDL variable has a data type. The possible type codes and their mapping to C language types are listed in the following table. The undefined type code (IDL_TYP_UNDEF) will always have the value zero.

Although it is rare, the number of types could change someday. Therefore, you should always use the symbolic names when referring to any type except IDL_TYP_UNDEF. Even in the case of IDL_TYP_UNDEF, using the symbolic name will add clarity to your code. Note that all IDL structures are considered to be of a single type (IDL_TYP_STRUCT).

Clearly, distinctions must be made between various structures, but such distinctions are made at a different level. There are a few constants that can be used to make your code easier to read and less likely to break if/when the idl_export.h file changes. These are:

IDL_MAX_TYPE—The value of the largest type.

IDL_NUM_TYPES—The number of types. Since the types are numbered starting at zero, IDL_NUM_TYPES is one greater than IDL_MAX_TYPE.

Table 5-1: IDL Types and Mapping to C
Name	Type	C Type
IDL_TYP_UNDEF	Undefined	<None>
IDL_TYP_BYTE	Unsigned byte	UCHAR
IDL_TYP_INT	16–bit integer	IDL_INT
IDL_TYP_LONG	32–bit integer	IDL_LONG
IDL_TYP_FLOAT	Single precision floating	float
IDL_TYP_DOUBLE	Double precision floating	double
IDL_TYP_COMPLEX	Single precision complex	IDL_COMPLEX
IDL_TYP_STRING	String	IDL_STRING
IDL_TYP_STRUCT	Structure	See Structure Variables
IDL_TYP_DCOMPLEX	Double precision complex	IDL_DCOMPLEX
IDL_TYP_PTR	32–bit integer	IDL_ULONG
IDL_TYP_OBJREF	32–bit integer	IDL_ULONG
IDL_TYP_UINT	Unsigned 16-bit integer	IDL_UINT
IDL_TYP_ULONG	Unsigned 32-bit integer	IDL_ULONG
IDL_TYP_LONG64	64-bit integer	IDL_LONG64
IDL_TYP_ULONG64	Unsigned 64-bit integer	IDL_ULONG64

Type Masks

There are some situations in which it is necessary to specify types in the form of a bit mask rather than the usual type codes, for example when a single argument to a function can represent more than a single type. For any given type, the bit mask value can be computed as: Mask = 2^TypeCode

The IDL_TYP_MASK preprocessor macro is provided to calculate these masks. Given a type code, it returns the bit mask. For example, to specify a bit mask for all the integer types:

IDL_TYP_MASK(IDL_TYP_BYTE)|IDL_TYP_MASK(IDL_TYP_INT)| 
                           IDL_TYP_MASK(IDL_TYP_LONG)

Specifying all the possible types would require a long statement similar to the one above. To avoid having to type so much for this common case, the IDL_TYP_B_ALL constant is provided.