[Bug fortran/66708] New: Possible (minor) improvement on formatted io with format too short

["gerhard dot steinmetz dot fortran at t-online dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66708

            Bug ID: 66708
           Summary: Possible (minor) improvement on formatted io with
                    format too short
           Product: gcc
           Version: 5.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gerhard.steinmetz.fortran@t-online.de
  Target Milestone: ---

Formatted read or write of a variable (list) needs a format (fmt)
string longer than 2 characters, because of parentheses ( ) and
at least one character for an edit descriptor (e.g. a, g0, i8).

At least if the fmt string is constant/unchangeable, an error message
could be given at compile time. Otherwise a runtime error occurs.
Here with write, same for read and print.


$ cat z_write_fmt_too_short_2_item.f90
program p
   character(2), parameter :: fmt1 = '()'
   character(2) :: fmt2 = '()'
   integer :: n = 1
 3 format ()
   write (*, fmt1) n
   write (*, fmt2) n
   write (*, '()') n
   write (*, 3) n
end


$ gfortran -g -O0 -Wall -fcheck=all z_write_fmt_too_short_2_item.f90
$ a.out
At line 6 of file z_write_fmt_too_short_2_item.f90 (unit = 6, file = 'stdout')
Fortran runtime error: Insufficient data descriptors in format after reversion