HP Fortran Programmer's Reference (September 2007)

Program units and procedures

Arguments

Chapter 7178

In the following code, the data object a is available to the subroutine as a consequence of

argument association and host association. The direct reference to a in the subroutine is

illegal.

PROGRAM p

CALL s (a,b)

CONTAINS

SUBROUTINE s (c,d)

c = 22.01 ! valid definition of a through the dummy

! argument

d = 3.0*a ! direct reference to a is ILLEGAL

...

END SUBROUTINE

END PROGRAM

INTENT attribute

To enable additional compile-time checking of arguments and to avoid possibly unwanted side

effects, the INTENT attribute can be declared for each dummy argument, which may be

speciﬁed as INTENT(IN), INTENT(OUT) or INTENT(INOUT).

The values that may be speciﬁed for the INTENT attribute have the following signiﬁcance:

• IN is used if the argument is not to be modiﬁed within the subprogram.

• OUT implies that the actual argument must not be used within the subprogram before it is

assigned a value.

• INOUT (the form IN OUT is also permitted) implies that the actual argument must be

deﬁned on entry and is deﬁnable within the subprogram.

See “INTENT (statement and attribute)” on page 388 for more information about the INTENT

attribute.

%VAL and %REF built-in functions

By default, HP Fortran passes noncharacter arguments by reference. Instead of passing the

value of the actual argument to the referenced procedure, Fortran passes its address, with

which the name of the dummy argument becomes associated—as explained in “Argument

association” on page 171. When HP Fortran passes character arguments, it includes a hidden

length parameter along with the address of the actual argument.

However, it is possible to change the way arguments are passed by using the %VAL and %REF

built-in functions, which HP Fortran provides as extensions: