FORTRAN 77 Language Reference

EXTERNAL

The EXTERNAL statement specifies procedures or dummy procedures as external, and allows their symbolic names to be used as actual arguments.

EXTERNAL proc [, proc] ...

Parameter 

Description 

proc

Name of external procedure, dummy procedure, or block data routine. 

Description

If an external procedure or a dummy procedure is an actual argument, it must be in an EXTERNAL statement in the same program unit.

If an intrinsic function name appears in an EXTERNAL statement, that name refers to some external subroutine or function. The corresponding intrinsic function is not available in the program unit.

Restrictions

A subroutine or function name can appear in only one of the EXTERNAL statements of a program unit.

A statement function name must not appear in an EXTERNAL statement.

Examples

Example 1: Use your own version of TAN:


       EXTERNAL TAN 
       T = TAN( 45.0 ) 
       ... 
       END 
       FUNCTION TAN( X ) 
       ... 
       RETURN 
       END 

Example 2: Pass a user-defined function name as an argument:


       REAL AREA, LOW, HIGH 
       EXTERNAL FCN 
       ... 
       CALL RUNGE ( FCN, LOW, HIGH, AREA ) 
       ... 
       END 

       FUNCTION FCN( X ) 
       ... 
       RETURN 
       END 

       SUBROUTINE RUNGE ( F, X0, X1, A ) 
       ... 
       RETURN 
       END