CALL

Invokes a subroutine.

Syntax

CALL subr-name[([ subr-act-arg-spec-list ])]

Description

A CALL statement is used to invoke (call) a subroutine, and to specify actual arguments, if any. Execution of the subroutine begins with the first executable statement. The sequence of events when a CALL statement is executed is as follows:

The correspondence between actual and dummy arguments is primarily by position: the first actual argument corresponds to the first dummy argument, the second to the second, and so on. The positional correspondence may be overridden by argument keywords, where a keyword name attached to an actual argument specifies a correspondence to the dummy argument of the same name. The following conditions govern the use of argument keywords:

A subroutine can call itself, directly or indirectly; in this case the keyword RECURSIVE must be added to the SUBROUTINE statement of the subroutine definition.

The %VAL and %REF built-in functions are provided as HP extensions. These allow cross-calling between languages by enabling arguments to be passed by value and by reference, respectively. %VAL causes its argument to be passed by value, as if to a C function; it is sign-extended to a 32-bit value if it is less than 32 bits. %REF causes its argument to be passed by reference, similar to the default Fortran 90 behavior, except that the hidden length parameter of a CHARACTER string is not passed.

The only subroutine invocation other than by the CALL statement in Fortran 90 is through "defined assignment", where a defined type assignment operator that has been defined by means of a subroutine is used. See the INTERFACE statement in this chapter for more information.

Examples

! Interface for subroutine draw

INTERFACE

   SUBROUTINE draw (x_start, y_start, x_end, &

                    y_end, form, scale)

      REAL x_start, y_start, x_end, y_end

      CHARACTER (LEN = 6), OPTIONAL :: form

      REAL, OPTIONAL :: scale

   END SUBROUTINE draw

END INTERFACE

! References to draw

CALL draw (5., -4., 2., .6, "DASHED")

! Arguments given by position.

! Optional argument scale omitted.

CALL draw (scale=.4, x_end=0., y_end=0., &

           x_start=.5, y_start=3.)

! Arguments given by keyword.

! Optional argument form omitted.

Related statements

INTERFACE and SUBROUTINE

Related concepts

The correspondence between the dummy arguments of a subroutine and the actual arguments specified in its invocation ("Argument association") is discussed in detail in Chapter 7, as are the other methods of association between a program unit and a subroutine called by it.