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NOTE: F2008 supports automatic allocation of a free unit with the NEWUNIT specifier in an OPEN statement. Beware that NEWUNIT-allocated LUNs are negative, so (lun>0) cannot no longer be used to check for a valid LUN. The only invalid LUN is -1.
(追記ここまで)(追記) (追記ここまで)#ifdef TESTPRG
program testit
integer,external :: notopen
write(*,*)'check for preassigned files from unit 0 to unit 1000'
write(*,*)'(5 and 6 always return -1)'
do i10=0,1000
if(notopen(i10,i10) .ne. i10)then
write(*,*)'INUSE:',i10, notopen(i10,i10)
endif
enddo
end program testit
#endif
!-------------------------------------------------------------------------------
FUNCTION NOTOPEN(ISTART,IEND)
!-------------------------------------------------------------------------------
! #(@)notopen(3f): find free FORTRAN unit number to OPEN() a file.
!
! NOTOPEN() returns a FORTRAN unit number from ISTART to IEND not
! currently associated with an I/O unit.
!
! If NOTOPEN() returns -1, then no free FORTRAN unit could be found,
! although all units were checked (except for units 5 and 6).
!
! Otherwise, notopen() returns an integer representing a
! free FORTRAN unit. Note that NOTOPEN() assumes units 5 and 6
! are special, and will never return those values.
!
! The range 1 to 99 is standard. Many machines allow other ranges
! and/or reserve certain units like 0 and 101 for standard input,
! standard output, ...
!
! An environment may impose a limit on the number of simultaneously
! open files (which some compilers work around); many systems extend
! the upper limit well above 99.
!-------------------------------------------------------------------------------
! Beginning with f2008, you can probably use OPEN(NEWUNIT=...) instead
!-------------------------------------------------------------------------------
USE ISO_FORTRAN_ENV, ONLY : ERROR_UNIT ! access computing environment
IMPLICIT NONE
INTEGER :: NOTOPEN ! function return value
INTEGER,INTENT(IN) :: ISTART ! unit number to start looking at
INTEGER,INTENT(IN) :: IEND ! last unit number to look at
INTEGER :: I10 ! counter from istart to iend
INTEGER :: IOS ! iostatus from INQUIRE
LOGICAL :: LOPEN ! returned from INQUIRE
NOTOPEN=(-1)
DO I10=ISTART,IEND
IF ( I10 ==5 .OR. I10 == 6 ) CYCLE ! always skip these two units
INQUIRE( UNIT=I10, OPENED=LOPEN, IOSTAT=IOS )
IF( IOS == 0 )THEN ! no error on INQUIRE
IF( .NOT. LOPEN )THEN ! if unit number not in use, return it
NOTOPEN = I10
EXIT ! only need to find one, so return
ENDIF
ELSE
WRITE(ERROR_UNIT,*)'*NOTOPEN*:E-R-R-O-R ON UNIT ',I10,'=',IOS
ENDIF
ENDDO
RETURN
END FUNCTION NOTOPEN
!-------------------------------------------------------------------------------