The IC C mapping (used by the C client and C server back-ends) follows the OMG C Language Mapping Specification.
The C mapping supports the following:
long double
and any
.
inout
parameters are not supported.
The following is not supported:
The IDL compiler reserves all identifiers starting with
OE_
and oe_
for internal use.
The C programmer must always use the global name for a type,
constant or operation. The C global name corresponding to an
OMG IDL global name is derived by converting occurrences of
"::" to underscore, and eliminating the leading "::". So, for
example, an operation op1
defined in interface
I1
which is defined in module M1
would be
written as M1::I1::op1
in IDL and as M1_I1_op1
in C.
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If underscores are used in IDL names it can lead to ambiguities due to the name mapping described above, therefore it is advisable to avoid underscores in identifiers. |
Two files will be generated for each scope. One set of files
will be generated for each module and each interface scope.
An extra set is generated for those definitions at top
level scope. One of the files is a header file(.h
), and the
other file is a C source code file (.c
). In addition to these
files a number of C source files will be generated for type encodings,
they are named according to the following template:
oe_code_<type>.c
.
For example:
// IDL, in the file "spec.idl" module m1 { typedef sequence<long> lseq; interface i1 { ... }; ... };
XXX This is C client specific.
Will produce the files oe_spec.h
and
oe_spec.c
for the top scope level. Then the files
m1.h
and m1.c
for the module m1
and
files m1_i1.h
and m1_i1.c
for the interface
i1
. The typedef will produce oe_code_m1_lseq.c
.
The header file contains type definitions for all
struct
types and sequences and constants in the IDL file. The
c file contains all operation stubs if the the scope is an interface.
In addition to the scope-related files a C source file will
be generated for encoding operations of all struct
and
sequence types.
The mapping of basic types is as follows.
OMG IDL type | C type | Mapped to C type |
float | CORBA_float | float |
double | CORBA_double | double |
short | CORBA_short | short |
unsigned short | CORBA_unsigned_short | unsigned short |
long | CORBA_long | long |
long long | CORBA_long_long | long |
unsigned long | CORBA_unsigned_long | unsigned long |
unsigned long long | CORBA_unsigned_long_long | unsigned long |
char | CORBA_char | char |
wchar | CORBA_wchar | unsigned long |
boolean | CORBA_boolean | unsigned char |
octet | CORBA_octet | char |
any | Not supported | |
long double | Not supported | |
Object | Not supported | |
void | void | void |
XXX Note that several mappings are not according to OMG C Language mapping.
Constructed types have mappings as shown in the following table.
OMG IDL type | Mapped to C type |
string | CORBA_char* |
wstring | CORBA_wchar* |
struct | struct |
union | union |
enum | enum |
sequence | struct (see below) |
array | array |
An OMG IDL sequence (an array of variable length),
// IDL typedef sequence <IDL_TYPE> NAME;
is mapped to a C struct as follows:
/* C */ typedef struct { CORBA_unsigned_long _maximum; CORBA_unsigned_long _length; C_TYPE* _buffer; } C_NAME;
where C_TYPE
is the mapping of IDL_TYPE
, and where
C_NAME
is the scoped name of NAME
.
An IDL constant is mapped to a C constant through a C
#define
macro, where the name of the macro is scoped.
Example:
// IDL module M1 { const long c1 = 99; };
results in the following:
/* C */ #define M1_c1 99
An OMG IDL operation is mapped to C function. Each C operation function has two mandatory parameters: a first parameter of interface object type, and a last parameter of environment type.
In a C operation function the the in
and out
parameters are located between the first and last parameters
described above, and they appear in the same order as in the IDL
operation declaration.
Notice that inout
parameters are not supported.
The return value of an OMG IDL operation is mapped to a corresponding return value of the C operation function.
Mandatory C operation function parameters:
CORBA_Object oe_obj
- the first parameter of a C
operation function. This parameter is required by the OMG
C Language Mapping Specification, but in the current
implementation there is no particular use for it.
CORBA_Environment* oe_env
- the last parameter of a C
operation function. The parameter is defined in the C header
file ic.h
and has the following public fields:
CORBA_Exception_type _major
- indicates if an
operation invocation was successful which will be one of
the following:
Example:
// IDL interface i1 { long op1(in long a); long op2(in string s, out long count); };
Is mapped to the following C functions
/* C */ CORBA_long i1_op1(i1 oe_obj, CORBA_long a, CORBA_Environment* oe_env) { ... } CORBA_long i1_op2(i1 oe_obj, CORBA_char* s, CORBA_long *count, CORBA_Environment* oe_env) { ... }
There is no standard CORBA mapping for the C-server side, as it is implementation-dependent but built in a similar way. The current server side mapping is different from the client side mapping in several ways:
Although exception mapping is not implemented, the stubs will generate CORBA system exceptions in case of operation failure. Thus, the only exceptions propagated by the system are built in system exceptions.
The user-defined parameters can only be in
or out
parameters, as
inout
parameters are not supported.
This table summarize the types a client passes as arguments to a stub, and receives as a result.
OMG IDL type | In | Out | Return |
short | CORBA_short | CORBA_short* | CORBA_short |
long | CORBA_long | CORBA_long* | CORBA_long |
long long | CORBA_long_long | CORBA_long_long* | CORBA_long_long |
unsigned short | CORBA_unsigned_short | CORBA_unsigned_short* | CORBA_unsigned_short |
unsigned long | CORBA_unsigned_long | CORBA_unsigned_long* | CORBA_unsigned_long |
unsigned long long | CORBA_unsigned_long_long | CORBA_unsigned_long_long* | CORBA_unsigned_long_long |
float | CORBA_float | CORBA_float* | CORBA_float |
double | CORBA_double | CORBA_double* | CORBA_double |
boolean | CORBA_boolean | CORBA_boolean* | CORBA_boolean |
char | CORBA_char | CORBA_char* | CORBA_char |
wchar | CORBA_wchar | CORBA_wchar* | CORBA_wchar |
octet | CORBA_octet | CORBA_octet* | CORBA_octet |
enum | CORBA_enum | CORBA_enum* | CORBA_enum |
struct, fixed | struct* | struct* | struct |
struct, variable | struct* | struct** | struct* |
union, fixed | union* | union* | union |
union, variable | union* | union** | union* |
string | CORBA_char* | CORBA_char** | CORBA_char* |
wstring | CORBA_wchar* | CORBA_wchar** | CORBA_wchar* |
sequence | sequence* | sequence** | sequence* |
array, fixed | array | array | array_slice* |
array, variable | array | array_slice** | array_slice* |
A client is responsible for providing storage of all arguments passed as in arguments.
OMG IDL type | Out | Return |
short | 1 | 1 |
long | 1 | 1 |
long long | 1 | 1 |
unsigned short | 1 | 1 |
unsigned long | 1 | 1 |
unsigned long long | 1 | 1 |
float | 1 | 1 |
double | 1 | 1 |
boolean | 1 | 1 |
char | 1 | 1 |
wchar | 1 | 1 |
octet | 1 | 1 |
enum | 1 | 1 |
struct, fixed | 1 | 1 |
struct, variable | 2 | 2 |
string | 2 | 2 |
wstring | 2 | 2 |
sequence | 2 | 2 |
array, fixed | 1 | 3 |
array, variable | 3 | 3 |
Case | Description |
1 | Caller allocates all necessary storage, except that which may be encapsulated and managed within the parameter itself. |
2 | 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. The caller is responsible for releasing the returned storage. 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 instance into a new instance, then modify the new instance. |
3 | The caller allocates a pointer to an array slice which has all the same dimensions of the original array except the first, and passes it by reference to the callee. The callee sets the pointer to point to a valid instance of the array. The caller is responsible for releasing the returned storage. 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 instance into a new instance, then modify the new instance. |
The returned storage in case 2 and 3 is allocated as one block of memory so it is possible to deallocate it with one call of CORBA_free.
CORBA_Environment *CORBA_Environment_alloc(int inbufsz, int outbufsz);
where :CORBA_char *CORBA_string_alloc(CORBA_unsigned_long len);
Thus far, no other type allocation function is supported.
void CORBA_free(void *storage)
void CORBA_exception_free(CORBA_environment *ev)
CORBA_char *CORBA_exception_id(CORBA_Environment *ev)
void *CORBA_exception_value(CORBA_Environment *ev)
erlang::binary
idl type has the same C-definition as
a generated sequence of octets :
module erlang { .... // an erlang binary typedef sequence<octet> binary; };it provides a way on sending trasparent data between C and Erlang.
typedef struct { CORBA_unsigned_long _maximum; CORBA_unsigned_long _length; CORBA_octet* _buffer; } erlang_binary; /* ERLANG BINARY */The differences (between
erlang::binary
and sequence< octet >
) are :
term_to_binary() / binary_to_term()
to create / extract binary structures.
erlang.idl
, while it's
C definition is located in the ic.h
header file, both in the
IC-< vsn >/include
directory.
The user will have to include the file erlang.idl
in order to use the
erlang::binary
type.
This is a small example of a simple stack. There are two operations on the stack, push and pop. The example shows all generated files as well as conceptual usage of the stack.
// The source IDL file: stack.idl struct s { long l; string s; }; interface stack { void push(in s val); s pop(); };
When this file is compiled it produces four files, two for the top scope and two for the stack interface scope. The important parts of the generated C code for the stack API is shown below.
stack.c
void push(stack oe_obj, s val, CORBA_Environment* oe_env) { ... } s* pop(stack oe_obj, CORBA_Environment* oe_env) { ... }
oe_stack.h
#ifndef OE_STACK_H #define OE_STACK_H /*------------------------------------------------------------ * Struct definition: s */ typedef struct { long l; char *s; } s; #endif
stack.h just contains an include statement of oe_stack.h
.
oe_code_s.c
int oe_sizecalc_s(CORBA_Environment *oe_env, int* oe_size_count_index, int* oe_size) { ... } int oe_encode_s(CORBA_Environment *oe_env, s* oe_rec) { ... } int oe_decode_s(CORBA_Environment *oe_env, char *oe_first, int* oe_outindex, s *oe_out) { ... }
The only files that are really important are the .h
files and the stack.c file.