https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100954
kargl at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |kargl at gcc dot gnu.org
--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Taco Jerkface from comment #0)
> Sample code:
>
> program inquire
> implicit none
> logical opened
> character(len=256) filename
> character(len=4) charstring
>
> integer iounit, itmp, ierr
>
> filename='testfile'
>
> iounit=-10
> inquire(iounit, opened=opened,iostat=ierr)
> ! not open yet
> write(*,*) 'Unit',iounit,'open?',opened,ierr
I believe the above is invalid Fortran. Fortran 2018, pp. 216-218
R1201 io-unit is file-unit-number
R1202 file-unit-number is scalar-int-expr
A unit is either an external unit or an internal unit. An external unit
is used to refer to an external file and is specified by an asterisk or
a file-unit-number. The value of file-unit-number shall be nonnegative,
equal to one of the named constants INPUT_UNIT, OUTPUT_UNIT, or ERROR_UNIT
of the intrinsic module ISO_FORTRAN_ENV (16.10.2), the unit argument of an
active defined input/output procedure (12.6.4.8), or a NEWUNIT value
(12.5.6.12).
In the above Fortran code, iounit is negative and it is not a NEWUNIT
value. There is some wiggle room, in that
All input/output statements are permitted to refer to units that exist.
The CLOSE, INQUIRE, and WAIT statements are also permitted to refer to
units that do not exist. No other input/output statement shall refer to
a unit that does not exist.
Your code could have done 'inquire(unit=42, opened=opened,iostat=ierr)'
where 42 is nonnegative and refers to a unit that does not exist. But,
iounit=-10 is negative and does not refer to a unit opened with NEWUNIT.
For NEWUNIT, the Fortran standard requires
The variable is defined with a processor determined NEWUNIT value...
A NEWUNIT value is a negative number, and shall not be equal to -1,
any of the named constants ERROR_UNIT, INPUT_UNIT, or OUTPUT_UNIT from
the intrinsic module ISO_FORTRAN_ENV (16.10.2), any value used by the
processor for the unit argument to a defined input/output procedure,
nor any previous NEWUNIT value that identifies a file that is connected.
The unit identified by a NEWUNIT value shall not be preconnected.
So, the Fortran standard does not require -10 to be a NEWUNIT value.
>
> ! new unit grabs -10
> open(newunit=iounit,file=trim(filename) )
> write(*,*) 'Opened unit',iounit
>
> ! now -10 is open
> inquire(iounit, opened=opened,iostat=ierr)
> write(*,*) 'Unit',iounit,'open?',opened,ierr
>
> ! close it
> close(iounit)
> write(*,*) 'Closed unit',iounit
The above is conforming as it seems that gfortran has assigned -10
as the unit number via the NEWUNIT mechanism. However, after the
close statement, there is no NEWUNIT value.
> ! now -10 is closed
> inquire(iounit, opened=opened,iostat=ierr)
> write(*,*) 'Unit',iounit,'open?',opened,ierr
See above as I believe that this is invalid Fortran.
> itmp=0
> write(charstring, '(I4.4)') itmp
> write(*,*) 'wrote into charstring ', trim(charstring)
>
>
> ! now -10 is reported as open again
> inquire(iounit, opened=opened,iostat=ierr)
> write(*,*) 'Unit',iounit,'open?',opened,ierr
Invalid code can yield unexpected results.
> ! trying to close it seg faults
> if (opened) then
> close(iounit)
> endif
>
> endprogram inquire
Of course, I could be wrong, so I'll leave this for other to pondered.
