HP 3000 Manuals

HP FORTRAN 77/iX Reference

EXTERNAL Statement (Nonexecutable) 

The EXTERNAL statement identifies a name as representing a subprogram
name and permits the name to be used as an actual argument in subprogram
calls.


            

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|                   |                                    |                                    |
|       Item        |        Description/Default         |            Restrictions            |
|                   |                                    |                                    |
-----------------------------------------------------------------------------------------------
|                   |                                    |                                    |
| procedure_name    | Name of a subprogram.              | Each name can appear once only in  |
|                   |                                    | a given EXTERNAL statement, and in |
|                   |                                    | at most one EXTERNAL statement in  |
|                   |                                    | a given program unit.              |
|                   |                                    |                                    |
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The EXTERNAL statement provides a means of using the names of subroutine
subprograms and function subprograms as actual arguments.  The EXTERNAL
statement is necessary to inform the compiler that these names are
subprograms or function names, not variable names.  Whenever a subprogram
name is passed as an actual argument, it must be placed in an EXTERNAL
statement in the calling program.  If an intrinsic function name appears
in an EXTERNAL statement, the compiler assumes that a user subprogram by
that name exists; the intrinsic function is not available to that program
unit.  A name cannot appear in both an EXTERNAL and INTRINSIC statement.

             Examples                                     Notes 

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PROGRAM my_sin                     This call is to the user-written function named
EXTERNAL sin                       sin, not to the intrinsic function SIN. A statement
REAL sin, x, y                     function name must not appear in an EXTERNAL
READ(5,*) y                        statement.
x = sin(y)
WRITE(6,*) x
END

EXTERNAL b1                        The EXTERNAL statement declares b1 to be a
CALL sub(a,b1,c)                   subprogram name.  The call to sub passes the values
  :                                of a and c, and passes the name of the subprogram
END                                (b1).

SUBROUTINE sub(x,y,z)              The reference to y causes b1 to be called.
z = y(z)
RETURN
END

MPE/iX 5.0 Documentation