DCE 1.1: Remote Procedure Call - IDL to C-language Mappings

CDE 1.1: Remote Procedure Call
Copyright © 1997 The Open Group

IDL to C-language Mappings

This appendix specifies the bindings of IDL data types to NDR data types and to a set of C-language defined data types. It also specifies the mapping of IDL syntax to the C-language syntax of generated stubs.

Data Type Bindings

The the data type mappings are specified in IDL/NDR/C Type Mappings . For definitions of the NDR data types, refer to Transfer Syntax NDR . Stubs use the C defined data types; to ensure portability, applications should use them as well. The C types shown in the last column of the table are recommended definitions for the C defined types for 32-bit machines.

IDL Type NDR Type Defined C Type C Type
boolean boolean idl_boolean unsigned char
char character idl_char unsigned char
byte uninterpreted octet idl_byte unsigned char
small small idl_small_int char
short short idl_short_int short int
long long idl_long_int long int
hyper hyper idl_hyper_int
16- or 32- Bit Machines:
Big Endian:
struct { long high; unsigned long low; }
Little Endian:
struct { unsigned long low; long high; }
64-Bit Machines:
long

unsigned small unsigned small idl_usmall_int unsigned char
unsigned short unsigned short idl_ushort_int unsigned short int
unsigned long unsigned long idl_ulong_int unsigned long int
unsigned hyper unsigned hyper idl_uhyper_int
16 or 32-Bit Machines:
Big Endian:
struct { unsigned long high; unsigned long low; }
Little Endian:
struct { unsigned long low; unsigned long high; }
64-Bit Machines:
unsigned long

float float idl_float float
double double idl_double double
handle_t not transmitted handle_t void *
error_status_t unsigned long idl_ulong_int unsigned long int
ISO_LATIN_1 uninterpreted octet ISO_LATIN_1 byte
ISO_MULTI_LINGUAL (Note 1.) ISO_MULTI_LINGUAL
struct{ byte row; byte column; }
ISO_UCS (Note 1.) ISO_UCS
struct{
byte group;
byte plane;
byte row;
byte column;
}

IDL Type	NDR Type	Defined C Type	C Type
boolean	boolean	idl_boolean	unsigned char
char	character	idl_char	unsigned char
byte	uninterpreted octet	idl_byte	unsigned char
small	small	idl_small_int	char
short	short	idl_short_int	short int
long	long	idl_long_int	long int
hyper	hyper	idl_hyper_int	16- or 32- Bit Machines: Big Endian: `struct { long high; unsigned long low; }` Little Endian: `struct { unsigned long low; long high; }` 64-Bit Machines: `long`
unsigned small	unsigned small	idl_usmall_int	unsigned char
unsigned short	unsigned short	idl_ushort_int	unsigned short int
unsigned long	unsigned long	idl_ulong_int	unsigned long int
unsigned hyper	unsigned hyper	idl_uhyper_int	16 or 32-Bit Machines: Big Endian: `struct { unsigned long high; unsigned long low; }` Little Endian: `struct { unsigned long low; unsigned long high; }` 64-Bit Machines: `unsigned long`
float	float	idl_float	float
double	double	idl_double	double
handle_t	not transmitted	handle_t	void *
error_status_t	unsigned long	idl_ulong_int	unsigned long int
ISO_LATIN_1	uninterpreted octet	ISO_LATIN_1	byte
ISO_MULTI_LINGUAL	(Note 1.)	ISO_MULTI_LINGUAL	`struct{ byte row; byte column; }`
ISO_UCS	(Note 1.)	ISO_UCS	struct{ byte group; byte plane; byte row; byte column; }

Table: IDL/NDR/C Type Mappings

The ISO_MULTILINGUAL and ISO_UCStypes are structures and are NDR encoded as constructed types.

The recommended values for the Boolean constants are specified in Recommended Boolean Constant Values .

Constant Value
TRUE 1
FALSE 0

Constant	Value
TRUE	1
FALSE	0

Table: Recommended Boolean Constant Values

Syntax Mappings

Unless specified otherwise, the code generated for the C language is syntactically identical to the IDL declarations. The following are the mappings from IDL to the C language for which the syntax is not identical to IDL. These mappings use the conventions, notation and productions defined in Interface Definition Language .

The interface header is not mapped to any C-language construct that is visible to users of RPC. (See Introduction to the RPC API for a discussion of interface handles.)
The import declaration causes definitions to be imported from other IDL source files. The import declaration itself has no associated C-language mapping.
All attributes (for example, <type_attribute>, <union_type_switch_attr>, <union_instance_switch_attr>, <usage_attribute>, <xmit_type>, <field_attribute>, <ptr_attr>, <operation_attribute>, <param_attribute>) and their associated [] (brackets), and punctuation are not mapped to the C language.

The IDL constant declaration:

const <const_type_spec> <Identifier> = <const_exp>

maps to the C language as:

#define <Identifier> (<const_exp>L)

The IDL non-encapsulated union declaration

union [ <tag> ] { <union_case_label_n_e> <union_arm> 
        [ <union_case_label_n_e> <union_arm> ] ...
        [ default : <union_arm> ]
      }

maps to the C language as:

union [ <tag> ] { <union_arm> [ <union_arm> ]... }

If an IDL <union_arm> is empty (that is, an instance resolves to only a ; (semicolon)), then no C mapping is generated for that arm.

The IDL encapsulated union declaration:

union [ <tag> ] switch ( <switch_type_spec> <Identifier> ) [<union_name> ]
    { <union_case_label> [ <union_case_label> ] ... <union_arm> 
        [ <union_case_label> [ <union_case_label> ] ... <union_arm> ] ...
    }

maps to the C language as:

struct [ <tag> ] 
   {
      <switch_type_spec> <Identifier> ;
      union { <union_arm> [ <union_arm> ]... } <union_name> ;
   }

If an IDL <union_arm> is empty (that is, an instance resolves to only a ; (semicolon)), then no C mapping is generated for that arm. If <union_name> is not present in the IDL declaration, then the union is assigned the name tagged_union.

The IDL pipe declaration:

pipe <type_spec> <pipe_declarators>

maps to the C language as:

typedef
   struct <pipe_declarators> {
      void (*pull) (
         char *state,
         <type_spec> *buf,
         idl_ulong_int esize,
         idl_ulong_int *ecount
      );
      void (*push) (
         char *state,
         <type_spec> *buf,
         idl_ulong_int *ecount
      );
      void (*alloc) (
         char *state,
         idl_ulong_int bsize,
         <type_spec> **buf,
         idl_ulong_int *bcount
      );
      char *state;
   }  <pipe_declarators> ;

The IDL array declarations in which all bounds of all dimensions evaluate to constants:

<Identifier> <[> <const_bounds> <]> [ <[> <const_bounds> <]> ] ...
<const_bounds> ::= <const_exp> | <lower> .. <upper>
<lower> ::= <Integer_literal> | <Identifier> 
<upper> ::= <Integer_literal> | <Identifier>

map to the C language as:

<Identifier> <[> <size> <]> [ <[> <size> <]> ] ...

where <size> is the value obtained by evaluating either <const_exp> or the expression (<upper>-<lower>+1).

IDL-conformant array declarations in which the size of the first dimension is determined at run time:

<Identifier> <[> [ <star_bounds> ] <]> [  <[> <const_bounds> <]> ] ...
<star_bounds> ::= * | <lower> .. * 
<const_bounds> ::= <const_exp> | <lower> .. <upper>
<lower> ::= <Integer_literal> | <Identifier> 
<upper> ::= <Integer_literal> | <Identifier>

when used in type definitions map to the C language as:

<Identifier> <[> 1 <]> [  <[> <size> <]> ] ...

and when used in parameter declarations map to the C language as:

<Identifier> <[> <]> [  <[> <size> <]> ] ...

where <size> is value obtained by evaluating either <const_exp> or the expression (<upper>-<lower>+1).

The manager EPV data type for an interface is determined by the interface definition specified in IDL. The relevant fields of an interface definition:

<[> uuid (<interface-uuid>),
    version (<major-version>.<minor-version>)
<]>
    interface <if-name>
{
    <type-decls>
    <type-1> <op1> (<params-1>);
[   <type-2> <op2> (<params-2>); ] ...
}

are mapped to the C-language structure:

typedef
    structure <if-name> v<major-version> <minor-varsion> epv t {
        <type-1> (* <op1>) (<params-1>);
      [ <type-2> (* <op2>) (<params-2>); ] ...
    }
        <if-name> v<major-version> <minor-version> epv t

where the IDL to C-language mappings have also been applied to the <type-1>, ..., and <params-1>, ..., declarations.

Mappings to languages other than C will be specified by The Open Group DCE as they become standardised.

Please note that the html version of this specification may contain formatting aberrations. The definitive version is available as an electronic publication on CD-ROM from The Open Group.

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