Open Watcom FORTRAN 77 Language Reference

FORTRAN Statements
2.43 EXTERNAL Statement
EXTERNAL p [,p] ...
where:
p
is the name of an external procedure, dummy procedure or block data subprogram.
The EXTERNAL statement identifies a symbolic name to be a dummy procedure or an external procedure
and allows these names to be passed as an actual argument. In the following example, SAM, ERRRTN and
POLY are declared to be external procedures.
Example:
EXTERNAL SAM, ERRRTN, POLY
In the following example, F is declared to be an external procedure and is passed as such to subroutine
SAM. If the EXTERNAL statement were eliminated then the variable F would be passed on to subroutine
SAM since there is no way of knowing that F is an external function.
Example:
EXTERNAL F
.
.
.
CALL SAM( F )
The appearance of an intrinsic function in an EXTERNAL statement declares that name to be an external
procedure and the intrinsic function by that name is no longer available in that program unit. This allows
the programmer to define a function by the same name as an intrinsic function. In the following example,
the programmer’s SIN function will be called instead of the intrinsic SIN function.
Example:
EXTERNAL SIN
.
.
.
CALL SIN( .1 )
A statement function name must not appear in an EXTERNAL statement. A name must only appear in an
EXTERNAL statement once.
EXTERNAL Statement 75