EXTERNAL Directive

The EXTERNAL directive allows an HP Pascal compilation unit to access an external routine (a routine in another compilation unit). The source code of the external routine can be any one of the following languages:

Syntax

Parameters

The programmer is responsible for matching the formal parameters and result type of the routine containing the EXTERNAL directive with the formal parameters and result type of the external routine. The matching rules are:

The INTRINSIC directive is more flexible about matching. See Chapter 10 “Intrinsics ” for details.

The EXTERNAL directive replaces the block in a routine declaration (see the HP Pascal/iX Reference Manual or the HP Pascal/HP-UX Reference Manual for details). The declaration containing the EXTERNAL directive can be at any level, but the external routine itself must be at level one in its own compilation unit.

Example 1

The Pascal program Pascal_Pascal calls the external Pascal procedure psubproc. This is the program:

$GLOBAL$
PROGRAM Pascal_Pascal(output);
CONST
   looplimit = 10;
TYPE
   loopbound = 1..looplimit;
VAR
   loop : loopbound;
   global,
   dynamic,
   static : integer;
PROCEDURE psubproc (    parm1 : integer;
                    VAR parm2 : integer); EXTERNAL;
BEGIN {pascal_pascal}
   dynamic := 0;
   FOR loop := 1 to looplimit DO BEGIN
      IF loop <= 5 THEN
         static := 10
      ELSE
         static := 20;
      global := loop;
      psubproc(static,dynamic);
      write('Cycle = ', loop, 'Total = ', dynamic);
   END;
   write('Finish processing');
END. {pascal_pascal}

This is the external Pascal procedure:

$EXTERNAL$
PROGRAM PASCALSUB;
VAR
   global : integer;
PROCEDURE psubproc (    adder : integer;
                    VAR total : integer);
VAR
   localconstant : integer;
BEGIN {psubproc}
   IF (global MOD 2) = 0 THEN
      localconstant := adder * 2
   ELSE
      localconstant := adder;
   total := total + localconstant;
END; {psubproc}
BEGIN
END.

You can use the EXTERNAL directive with procedure declarations in the implement part of a module. In such a procedure declaration, repeating the formal parameters is optional. If you do repeat them, they must be identical to those in the export section.

Example 2

MODULE m;
EXPORT
   PROCEDURE proc1 (VAR parm1 : integer;
                    VAR parm2 : char);
   PROCEDURE proc2 (VAR parm1 : integer);
IMPLEMENT
   PROCEDURE proc1;  {formal parameters omitted}
      EXTERNAL;
   PROCEDURE proc2 (VAR parm1 : integer);  {formal parameter repeated}
      EXTERNAL;
END;

Use the EXTERNAL directive in exported procedures to link routines written in other languages into your program. You are responsible for ensuring that the formal parameters of the exported procedure correspond to those of the actual external procedure.

	NOTE: Do not confuse the EXTERNAL directive with the EXTERNAL compiler option. Refer to the HP Pascal/iX Reference Manual or the HP Pascal/HP-UX Reference Manual, depending on your implementation, for information on the EXTERNAL compiler option.