Portability of Code


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Programming a BEA Tuxedo Application Using TxRPC

Portability of Code

The output from the IDL compiler is generated in a way to allow it to be compiled in a large number of environments (see the next chapter for a discussion of compilation). However, there are some constructs that don't work in various environments. Here are a few known problems.

When compiling with Classic (non-ANSI) C, "pointers to arrays" are not allowed. For example:

typedef long array[10][10];
func()
  {
  array t1;
  array *t2;
  t2 = &t1;   /* & ignored, invalid assignment */
  func2(&t1); /* & ignored */
  }

This will make it difficult to pass "pointers to arrays" to operations as parameters in a portable fashion.

When using an array of strings where the string attribute is applied to a multi-byte structure, the results will not be as desired if the compiler pads the structure. This is not the normal case (most compilers do not pad a structure that contains only character fields), but at least one occurrence is known to exist.

Constant values are, by default, implemented by generating a #define for each constant. This means that names used for constants should not be used for any other names in the IDL file or any imported IDL files. A TxRPC-specific option on the tidl compiler, -use_const, may be used to get around this problem in an ANSI C environment. This option will cause const declarations instead of #define definitions to be generated. The constant values will be declared in the client and server stubs, and any other source file including the header file will simply get extern const declarations. Note that this has the restriction that the client and server stubs may not be compiled into the same executable file (or duplicate definition errors will occur).

There are several restrictions in the C++ environment:

Do not use the same name for a typedef and a structure or union tag, unless the typedef name matches the struct or union name.
```
struct t1 {
  long s1;
};
typedef struct t1 t1; /* ok */
typedef long t1; /* error */
```
Do not hide a structure or union tag declaration inside another structure or union declaration and then reference it outside.
```
struct t1 {
  struct t2 {
   long s2;
} s1;
} t1;
typedef struct t3 {
struct t2 s3; /* t2 undefined error */
} t3;
```
Some compiler warnings may be generated. These include the following:
- Warnings that automatic variables are declared but not used
- Warnings that a variable is used before being set when referenced in sizeof() as in the following case.
```
long *ptr;
ptr = (long *)malloc(sizeof(*ptr) * 4);
```

When coding the client and server application software, you should use the data types generated by the IDL compiler, as defined in rpc/tidlbase.h (listed as Emitted Macro in the following table). For instance, if you use a long instead of idl_long_int, then the data type may be 32 bits on some platforms and 64 bits on others; idl_long_int will be 32 bits on all platforms. Here is a table that lists the generated data types.

IDL Type
Size
Emitted Macro
C Type

boolean

8 bits

idl_boolean

unsigned char

char

8 bits

idl_char

unsigned char

byte

8 bits

idl_byte

unsigned char

small

8 bits

idl_small_int

char

short

16 bits

idl_short_int

short

long

32 bits

idl_long_int

Machines with 32-bit long: long Machines with 64-bit long: int

hyper

64 bits

idl_hyper_int

Machines with 32-bit long:
Big Endian

struct
{
long high;
unsigned long low;
}

Little Endian

struct
{
unsigned long low;
long high;
}

Machines with 64-bit long:

long

unsigned small

8 bits

idl_usmall_int

unsigned char

unsigned short

16 bits

idl_ushort_int

short

unsigned long

32 bits

idl_ulong_int

Machines with 32-bit long: long Machines with 64-bit long: int

unsigned hyper

64 bits

idl_uhyper_int

Machines with 32-bit long:
Big Endian

struct
{
unsigned long high;
unsigned long low;
}

Little Endian

struct
{
unsigned long low;
unsigned long high;
}

Machines with 64-bit long:

unsigned long

float

32 bits

idl_short_float

float

double

64 bits

idl_long_float

double

void *

pointer

idl_void_p_t

void *

handle_t

pointer

handle_t

handle_t

IDL Type	Size	Emitted Macro	C Type
boolean	8 bits	idl_boolean	unsigned char
char	8 bits	idl_char	unsigned char
byte	8 bits	idl_byte	unsigned char
small	8 bits	idl_small_int	char
short	16 bits	idl_short_int	short
long	32 bits	idl_long_int	Machines with 32-bit long: long Machines with 64-bit long: int
hyper	64 bits	idl_hyper_int	Machines with 32-bit long: Big Endian struct { long high; unsigned long low; } Little Endian struct { unsigned long low; long high; } Machines with 64-bit long: long
unsigned small	8 bits	idl_usmall_int	unsigned char
unsigned short	16 bits	idl_ushort_int	short
unsigned long	32 bits	idl_ulong_int	Machines with 32-bit long: long Machines with 64-bit long: int
unsigned hyper	64 bits	idl_uhyper_int	Machines with 32-bit long: Big Endian struct { unsigned long high; unsigned long low; } Little Endian struct { unsigned long low; unsigned long high; } Machines with 64-bit long: unsigned long
float	32 bits	idl_short_float	float
double	64 bits	idl_long_float	double
void *	pointer	idl_void_p_t	void *
handle_t	pointer	handle_t	handle_t

As in C, there are several classes of identifiers in the IDL. Names within each class (that is, scope or name space) must be unique:

Constant, typedef, operation, and enumeration member names are in one name space.
Structure, union, and enumeration tags are in another name space.
Structure and union member names at the same level must be unique within the structure or union in which they are defined.
Parameter names within the operation prototype in which they are defined must be unique.

Note that an anonymous structure or union (without a tag and not defined as part of a typedef) cannot be used for an operation return or a parameter.