13.5.1 Operation Parameters and Signatures

The following table displays the mapping for the basic OMG IDL parameter passing modes and return type according to the type being passed or returned. The following table displays the same information for T_var types. The following table is merely for informational purposes; it is expected that operation signatures for both clients and servers will be written in terms of the parameter-passing modes shown in the following table, with the exception that the T_out types will be used as the actual parameter types for all out parameters.

It is also expected that T_var types will support the necessary conversion operators to allow them to be passed directly. Callers must always pass instances of either T_var types or the base types shown in the following table, and callees must treat their T_out parameters as if they were actually the corresponding underlying types shown in the following table.

In following table, fixed-length arrays are the only case where the type of an out

parameter differs from a return value, which is necessary because C++ does not allow a function to return an array. The mapping returns a pointer to a slice of the

array, where a slice is an array with all the dimensions of the original array

specified except the first dimension.

Table 13-7 Basic Argument and Result Passing

Data Type	In	Inout	Out	Return
short	Short	Short&	Short&	Short
long	Long	Long&	Long&	Long&
unsigned short	UShort	UShort&	UShort&	UShort&
unsigned long	ULong	ULong&	ULong&	ULong&
float	Float	Float&	Float&	Float&
double	Double	Double&	Double&	Double&
boolean	Boolean	Boolean&	Boolean&	Boolean&
char	Char	Char&	Char&	Char&
wchar	WChar	WChar&	WChar&	WChar&
octet	Octet	Octet&	Octet&	Octet&
enum	enum	enum&	enum&	enum&
object reference ptr (See Note below.)	objref_ptr	objref_ptr&	objref_ptr&	objref_ptr
struct, fixed	const struct&	struct&	struct&	struct
struct, variable	const struct&	struct&	struct*&	struct*
union, fixed	const union&	union&	union&	union
union, variable	const union*	union&	union&	union
string	const char	char*&	char*&	char*
wstring	const WChar	WChar*&	WChar*&	WChar*
sequence	const sequence&	sequence&	sequence*&	sequence*
array, fixed	const array	array	array	array slice * (See Note below.)
array, variable	const array	array	array slice *&	array slice *
any	const any&	any&	any*&	any*

Note:

The Object reference ptr data type includes pseudo-object references. The array slice return is an array with all the dimensions of the original array except the first dimension.

A caller is responsible for providing storage for all arguments passed as in arguments.

Table 13-8 T_var Argument and Result Passing

Data Type	In	Inout	Out	Return
object reference var (See Note below.)	const object	objref_var&	objref_var&	objref_var
struct_var	const struct_var&	struct_var&	struct_var&	struct_var
union_var	const union_var&	union_var&	union_var&	union_var
string_var	const string_var&	string_var&	string_var&	string_var
sequence_var	const sequence_var&	sequence_var&	sequence_var&	sequence_var
array_var	const array_var&	array_var&	array_var&	array_var
any_var	const any_var&	any_var&	any_var&	any_var

Note:

The object reference var data type includes pseudo-object references.

The following table and table describe the caller’s responsibility for storage associated with inout and out parameters and for return results.

Table 13-9 Caller Argument Storage Responsibilities

Type	Inout Param	Out Param	Return Result
short	1	1	1
long	1	1	1
unsigned short	1	1	1
unsigned long	1	1	1
float	1	1	1
double	1	1	1
boolean	1	1	1
char	1	1	1
wchar	1	1	1
octet	1	1	1
enum	1	1	1
object reference ptr	2	2	2
struct, fixed	1	1	1
struct, variable	1	3	3
union, fixed	1	1	1
union, variable	1	3	3
string	4	3	3
wstring	4	3	3
sequence	5	3	3
array, fixed	1	1	6
array, variable	1	6	6
any	5	3	3

In particular, exception used as a data type and a function name.

Table 13-10 Argument Passing Cases

Case
1	Caller allocates all necessary storage, except that which may be encapsulated and managed within the parameter itself. For inout parameters, the caller provides the initial value, and the callee may change that value. For out parameters, the caller allocates the storage but need not initialize it, and the callee sets the value. Function returns are by value.
2	Caller allocates storage for the object reference. For inout parameters, the caller provides an initial value; if the callee wants to reassign the inout parameter, it will first call CORBA::release on the original input value. To continue to use an object reference passed in as an inout, the caller must first duplicate the reference. The caller is responsible for the release of all out and return object references. Release of all object references embedded in other structures is performed automatically by the structures themselves.
3	For out parameters, the caller allocates a pointer and passes it by reference to the callee. The callee sets the pointer to point to a valid instance of the parameter’s type. For returns, the callee returns a similar pointer. The callee is not allowed to return a NULL pointer in either case. In both cases, the caller is responsible for releasing the returned storage. To maintain local/remote transparency, the caller must always release the returned storage, regardless of whether the callee is located in the same address space as the caller or is located in a different address space. Following the completion of a request, the caller is not allowed to modify any values in the returned storage—to do so, the caller must first copy the returned instance into a new instance, and modify the new instance.
4	For inout strings, the caller provides storage for both the input string and the char* pointing to it. Since the callee may deallocate the input string and reassign the char* to point to new storage to hold the output value, the caller should allocate the input string using string_alloc(). The size of the out string is, therefore, not limited by the size of the in string. The caller is responsible for deleting the storage for the out using string_free(). The callee is not allowed to return a NULL pointer for an inout, out, or return value.
5	For inout sequences and anys, assignment or modification of the sequence or any may cause deallocation of owned storage before any reallocation occurs, depending upon the state of the Boolean release parameter with which the sequence or any was constructed.
6	For out parameters, the caller allocates a pointer to an array slice, which has all the same dimensions of the original array except the first, and passes the pointer by reference to the callee. The callee sets the pointer to point to a valid instance of the array. For returns, the callee returns a similar pointer. The callee is not allowed to return a NULL pointer in either case. In both cases, the caller is responsible for releasing the returned storage. To maintain local/remote transparency, the caller must always release the returned storage, regardless of whether the callee is located in the same address space as the callee or is located in a different address space. Following completion of a request, the caller is not allowed to modify any values in the returned storage—to do so, the caller must first copy the returned array instance into a new array instance, and modify the new instance.