HP UX Fortran Software manual Syntax, Description and restrictions, Name, External-name

In files that use free format, directives must start with the comment character!. In fixed format, they must start with the comment character C, *, or !in column 1. Keywords and any arguments must be delimited by at least one space character, as in the following:

!$HP$ OPTIMIZE ON

Using the comment character as the directive prefix ensures that, unless the compiler is specifically looking for the directive, it is otherwise treated as a comment and ignored.

The following sections describe each of the HP Fortran directives.

$HP$ ALIAS

The ALIASdirective associates the name of a subroutine, function, entry, or common block with an external name and specifies the parameter-passing conventions of routines written in other languages.

Syntax

!$HP$ ALIAS name [= external-name ] [(arg-pass-mode-list)]

name	is the name used by the program to refer to a subroutine, function, or procedure entry point—but
	not to an internal subroutine. If name is enclosed by slashes, it is a common block name.
external-name	is a character constant that specifies a standard symbolic name.

arg-pass-mode-listis used only when name is that of a procedure that takes arguments. The items in the list specify how the corresponding actual argument are to be passed. The items can be either of the following built-in functions:

•%VAL: pass the value of the actual argument

•%REF: pass the address of the actual argument

There must be as many items in the list as there are arguments in the procedure, they must be separated by commas, and they must correspond positionally to the arguments.

Description and restrictions

The $HP$ ALIAS directive serves two purposes:

•It provides a way to associate the name used by your program when referring to a subroutine, function, entry, or common block with a distinct external name. This feature is especially useful when you want to access a variety of different graphics device drivers from the same source code so that different hardware configurations can be supported.

•When used in conjunction with the %VALand %REFbuilt-in functions, it provides a way to direct the compiler to use the appropriate parameter passing conventions to communicate with routines written in other high-level languages. Using Fortran directives

external-nameshould never conflict with the name of an HP-UX system routine (described in sections 2 and 3 of the HP-UX Reference) or with a Fortran library routine (for example, OPEN, READ, or CLOSE). The $HP$ ALIASdirective applies to subroutines, entries, and functions that are used externally. It does not apply to the main program unit.

%VAL is a built-in function that specifies that the value of the actual argument is to be passed to the called procedure. You can use this parameter with all types of arguments. However, when used with a procedure name, it has no effect; a pointer to the procedure is still passed.

%REFspecifies that the address of the actual argument is to be passed to the called procedure. For non-character arguments, this is the default. For character arguments, %REF disables the passing of the hidden length parameter.

When %VALand %REF are used with the CALL statement, they override the specification in the $HP$ ALIASdirective. For detailed information about these built-in functions and their use in the CALL statement, see the HP Fortran Programmer’s Reference.

124 Using Fortran directives