http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48618
Summary: Negative unit number in OPEN(...) is sometimes allowed
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libfortran
AssignedTo: [email protected]
ReportedBy: [email protected]
From F2008 9.5.1 paragraph 2:
"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 (13.8.2), or a NEWUNIT value (9.5.6.12)."
That is, consider:
program unittest
implicit none
open(10, file="foo.txt")
open(10, file="bar.txt")
end program unittest
The second open will close the file foo.txt and open bar.txt on the existing
unit. Similarly,
program nutest
implicit none
integer :: id
open(newunit=id, file="foo.txt")
open(id, file="bar.txt")
end program nutest
should work ("...or a NEWUNIT value" in 9.5.1), but
$ ./a.out
At line 5 of file nutest.f90
Fortran runtime error: Bad unit number in OPEN statement
However for
program negunit
implicit none
open(-10, file="foo.txt")
end program negunit
we are correct to generate the error
$ ./negunit
At line 3 of file negunit.f90
Fortran runtime error: Bad unit number in OPEN statement
as the unit number does not refer to an existing unit. That is, we must change
the logic such that we generate an error for negative unit number in the OPEN
statement only after we make sure that the unit doesn't exist.
