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A Compaq PL/I variable with the EXTERNAL attribute corresponds to a FORTRAN common block and to a Compaq C extern variable in the common_block external model. Example 3-16 and Example 3-17 show how a program section is shared between Compaq C and Compaq PL/I.
A PL/I EXTERNAL CHARACTER attribute corresponds to a Compaq C extern char variable, but PL/I character strings are not necessarily null-terminated. In Example 3-16, Compaq C and Compaq PL/I use the same variable to manipulate the character string that resides in a program section named XYZ.
| Example 3-16 Sharing Data with a PL/I Program in Named Program Sections |
|---|
/* PL/I program PRSTRING.PLI contains the following lines of code: */
PRSTRING: PROCEDURE;
DECLARE XYZ EXTERNAL CHARACTER(20);
PUT SKIP LIST(XYZ);
RETURN;
END PRSTRING;
/* End of PL/I program */
/* Compaq C program STRING.C contains the following lines of *
* code: */
main(void)
{
extern char xyz[20];
strncpy(xyz,"This is a string ", sizeof xyz);
prstring();
}
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The PL/I procedure PRSTRING writes out the contents of the external variable xyz .
PL/I also has a structure type similar (in its internal representation) to the struct keyword in Compaq C. Moreover, Compaq PL/I can output aggregates, such as structures and arrays, in fairly simple stream-output statements; consider Example 3-17.
| Example 3-17 Sharing Data with a PL/I Program in a Compaq C Structure |
|---|
/* PL/I program FNUM.PLI contains the following lines of code: */
FNUM: PROCEDURE;
/* EXTERNAL STRUCTURE CONTAINING THREE INTEGERS */
DECLARE 1 NUMBERS EXTERNAL,
2 FIRST FIXED(31),
2 SECOND FIXED(31),
2 THIRD FIXED(31);
PUT SKIP LIST('Contents of structure:',NUMBERS);
RETURN;
END FNUM;
/* End of PL/I program */
/* Compaq C program NUMBERS.C contains the following lines of *
* code: */
struct xs
{
int first;
int second;
int third;
};
main()
{
extern struct xs numbers;
numbers.first = 1;
numbers.second = 2;
numbers.third = 3;
fnum();
}
|
The PL/I procedure FNUM writes out the complete contents of the
external structure NUMBERS; the structure members are written out in
the order of their storage in memory, which is the same as for a
Compaq C structure.
3.4.3 Sharing Program Sections with MACRO Programs
In a MACRO program, the .PSECT directive sets up a separate program section that can store data or MACRO instructions. The attributes in the .PSECT directive describe the contents of the program section.
Example 3-18 shows how to set up a psect in a MACRO program that allows data to be shared with a Compaq C program.
| Example 3-18 Sharing Data with a MACRO Program in a Compaq C Structure |
|---|
; MACRO source file SET_VALUE.MAR contains the following lines of code:
.entry set_value,^M<>
movl #1,first
movl #2,second
movl #3,third
ret
.psect example pic,usr,ovr,rel,gbl,noshr,-
noexe,rd,wrt,novec,long
first: .blkl
second: .blkl
third: .blkl
.end
; End of MACRO source file
/* Compaq C program NUMBERS.C contains the following lines of *
* code: */
#pragma extern_model common_block
struct xs
{
int first;
int second;
int third;
} example;
main()
{
set_value();
printf("example.first = %d\n", example.first);
printf("example.second = %d\n", example.second);
printf("example.third = %d\n", example.third);
}
|
The MACRO program initializes the locations first, second, and third in the psect named example and passes these values to the Compaq C program. The locations are referenced in the Compaq C program as members of the external structure named example .
Also, note the
#pragma extern_model common_block
preprocessor directive. This directive sets the model for external
variables to the
common_block
model, which is the one used by VAX C. The default external model for
Compaq C is the
relaxed_refdef
model. For more information on the
#pragma extern_model common_block
preprocessor directive, see Section 5.4.5.
3.5 OpenVMS Run-Time Library Routines
The OpenVMS Run-Time Library (RTL) is a library of prewritten, commonly used routines that perform a wide variety of functions. These routines are grouped according to the types of tasks they perform, and each group has a prefix that identifies those routines as members of a particular OpenVMS RTL facility. Table 3-10 lists all the language-independent, run-time library facility prefixes and the types of tasks each facility performs.
| Facility Prefix | Types of Tasks Performed |
|---|---|
| DTK$ | DECtalk routines that are used to control the DIGITAL DECtalk device. |
| LIB$ | Library routines that obtain records from devices, manipulate strings, convert data types for I/O, allocate resources, obtain system information, signal exceptions, establish condition handlers, enable detection of hardware exceptions, and process cross-reference data. |
| MTH$ | Mathematics routines that perform arithmetic, algebraic, and trigonometric calculations. |
| OTS$ | General-purpose routines that perform tasks such as data-type conversions as part of a compiler's generated code. |
| SMG$ | Screen management routines that are used in designing, composing, and keeping track of complex images on a video screen. |
| STR$ | String manipulation routines that perform such tasks as searching for substrings, concatenating strings, and prefixing and appending strings. |
The OpenVMS run-time library routines are documented in detail in the following operating system documentation:
System services are prewritten system routines that perform a variety of tasks, such as controlling processes, communicating among processes, and coordinating I/O.
Unlike the OpenVMS Run-Time Library (RTL) routines, which are divided into groups by facility, all system services share the same facility prefix (SYS$). However, these services are logically divided into groups that perform similar tasks. Table 3-11 describes these groups.
| Group | Types of Tasks Performed |
|---|---|
| AST | Allows processes to control the handling of asynchronous system traps (ASTs). |
| Change mode | Changes the access mode of particular routines. |
| Condition handling | Designates condition handlers for special purposes. |
| Event flag | Clears, sets, reads, and waits for event flags, and associates with event flag clusters. |
| Information | Returns information about the system, queues, jobs, processes, locks, and devices. |
| Input/Output | Performs I/O directly without going through RMS. |
| Lock management | Enables processes to coordinate access to shareable system resources. |
| Logical names | Provides methods of accessing and maintaining pairs of character-string logical names and equivalence names. |
| Memory management | Increases or decreases available virtual memory, controls paging and swapping, and creates and accesses shareable files of code or data. |
| Process control | Creates, deletes, and controls execution of processes. |
| Security | Enhances the security of OpenVMS systems. |
| Time and Timing | Schedules events and obtains and formats binary time values. |
System services are documented in detail in the OpenVMS System Services Reference Manual.
The routines that provide a programming interface to various OpenVMS
utilities are described in the OpenVMS Utility Routines Manual.
3.7 Calling Routines
The basic steps for calling routines are the same whether you are
calling a routine written in Compaq C, a routine written in some
other OpenVMS language, a system service, or an
OpenVMS Run-Time Library (RTL) routine. The following sections
outline the procedures for calling non-Compaq C routines.
3.7.1 Determining the Type of Call
Before calling an external routine, you must first determine whether
the call should be a procedure call or a function call. Call a routine
as a procedure if it does not return a value. Call a routine as a
function if it returns any type of value.
3.7.2 Declaring an External Routine and Its Arguments
To call an external routine or system routine, you need to declare it as an external function and to declare the names, data types, and passing mechanisms of its arguments. Arguments can be either required or optional.
Include the following information in a routine declaration:
The following example shows how to declare an external routine and its arguments:
char func_name (int x, char y); |
Header files are available to declare commonly used external routines.
Using them will save you a lot of work. See Sections 1.3.1.1 and
1.3.1.2 in this manual for information on listing and including
header files.
3.7.3 Calling the External Routine
After declaring an external routine, you can invoke it. To invoke a function, you must specify the name of the routine being invoked and all arguments required for that routine. Make sure the data types for the actual arguments you are passing coincide with those of the parameters you declared earlier, and with those declared in the routine. The following example shows how to invoke the function declared in Section 3.7.2:
ret_status = func_name(1,'a'); |
All system routine arguments are described in terms of the following information:
OpenVMS usages are data structures that are layered on the standard OpenVMS data types. For example, the OpenVMS usage mask_longword signifies an unsigned longword integer that is used as a bit mask, and the OpenVMS usage floating_point represents any OpenVMS floating-point data type. Table 3-12 lists all the OpenVMS usages and the Compaq C types you need to implement them.
| OpenVMS Data Type | Compaq C Declaration |
|---|---|
| access_bit_names | user-defined 1 |
| access_mode | unsigned char |
| address | int *pointer 2,4 |
| address_range | int *array [2] 2,3,4 |
| arg_list | user-defined 1 |
| ast_procedure | pointer to a function 2 |
| boolean | unsigned long int |
| byte_signed | char |
| byte_unsigned | unsigned char |
| channel | unsigned short int |
| char_string | char array[n] 3,5 |
| complex_number | user-defined 1 |
| cond_value | unsigned long int |
| context | unsigned long int |
| date_time | user-defined 1 |
| device_name | char array[n] 3,5 |
| ef_cluster_name | char array[n] 3,5 |
| ef_number | unsigned long int |
| exit_handler_block | user-defined 1 |
| fab |
#include fab from text library
struct FAB |
| file_protection | unsigned short int, or user-defined 1 |
| floating_point | float or double |
| function_code | unsigned long int or user-defined 1 |
| identifier | int *pointer 2,4 |
| io_status_block | user-defined 1 |
| item_list_2 | user-defined 1 |
| item_list_3 | user-defined 1 |
| item_list_pair | user-defined 1 |
| item_quota_list | user-defined 1 |
| lock_id | unsigned long int |
| lock_status_block | user-defined 1 |
| lock_value_block | user-defined 1 |
| logical_name | char array[n] 3,5 |
| longword_signed | long int |
| longword_unsigned | unsigned long int |
| mask_byte | unsigned char |
| mask_longword | unsigned long int |
| mask_quadword | user-defined 1 |
| mask_word | unsigned short int |
| null_arg | unsigned long int |
| octaword_signed | user-defined 1 |
| octaword_unsigned | user-defined 1 |
| page_protection | unsigned long int |
| procedure | pointer to function 2 |
| process_id | unsigned long int |
| process_name | char array[n] 3,5 |
| quadword_signed | user-defined 1 |
| quadword_unsigned | user-defined 1 |
| rights_holder | user-defined 1 |
| rights_id | unsigned long int |
| rab |
#include rab
struct RAB |
| section_id | user-defined 1 |
| section_name | char array[n] 3,5 |
| system_access_id | user-defined 1 |
| time_name | char array[n] 3,5 |
| uic | unsigned long int |
| user_arg | user-defined 1 |
| varying_arg | user-defined 1 |
| vector_byte_signed | char array[n] 3,5 |
| vector_byte_unsigned | unsigned char array[n] 3,5 |
| vector_longword_signed | long int array[n] 3,5 |
| vector_longword_unsigned | unsigned long int array[n] 3,5 |
| vector_quadword_signed | user-defined 1 |
| vector_quadword_unsigned | user-defined 1 |
| vector_word_signed | short int array[n] 3,5 |
| vector_word_unsigned | unsigned short int array[n] 3,5 |
| word_signed | short int |
| word_unsigned | unsigned short int |
If a system routine argument is optional, it will be indicated in the format section of the routine description in one of two ways, as follows:
If the comma appears outside the brackets, you must pass a 0 by value to indicate the place of the omitted argument. If the comma appears inside the brackets, you can omit the argument if it is the last argument in the list.
For more information, see the OpenVMS Programming Interfaces: Calling a System Routine manual. This manual describes the OpenVMS programming interface and defines the standard conventions to call an OpenVMS system routine from a user procedure. The Alpha and VAX data type implementations for various high-level languages are also presented.
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