HP Fortran Programmer's Reference (September 2007)

Program units and procedures

Internal procedures

Chapter 7 167

Internal procedures

An internal procedure is similar to an external procedure except that:

• It must be deﬁned within a hosting program unit—a main, external, or module program

unit—following the CONTAINS statement.

• It can be referenced by the host only.

• It can access other entities by host association within the host.

• It cannot have an ENTRY statement.

• It cannot be passed as an argument.

• It cannot contain an internal procedure.

The syntax of an internal procedure deﬁnition is the same as for an external procedure (see

“Procedure deﬁnition” on page 161), except that it has no internal procedure part. The

reference to an internal procedure is the same as for an external procedure; see “Procedure

reference” on page 162.

The following example, int_func.f90, declares and references an internal function. Note that

both the external procedure and the internal procedure have an assumed-shape array as a

dummy argument, which requires the procedure to have an explicit interface (see “Procedure

interface” on page 181). External procedures must be declared in an interface block to make

their interface explicit; the interface of internal procedures is explicit by default.

Example 7-2 int_func.f90

PROGRAM main

! declare and initialize an array to pass to an external

! procedure

REAL, DIMENSION(3) :: values = (/2.0, 5.0, 7.0/)

! Because the dummy argument to print_avg is an assumed-shape

! array (see the definition of print_avg below), the

! procedure interface of print_avg must

! be made explicit within the calling program unit.

INTERFACE

SUBROUTINE print_avg(x)

REAL :: x(:)

END SUBROUTINE print_avg

END INTERFACE

CALL print_avg(values)