Error: Nonnegative width required in format string at (1)

Question

I'm trying to compile a piece of code with gfortran and it's failing with the following error:

Error: Nonnegative width required in format string at (1)
../src/powmes.f90:410.20:
     write(lunit,'(I,E,E,E)') wavenum(k),power(k),nmodes(k),errorexpan(k)

414   if (filepower_fold(1:1) /= '#') then
415      fileout=trim(filepower_fold)//'.waven'
416      if (verbose) write(*,*) 'Output '//trim(fileout)
417      open(file=fileout,form='formatted',status='unknown',unit=lunit,err=2)
418      do k=0,ngrid/2
419         do ifold=0,nfoldpow-1
420            write(lunit,'(I,$)') waven(k,ifold)
421         enddo
422         write(lunit,'(I)') waven(k,nfoldpow)
423      enddo
424      close(lunit)

How can I compile this?

Solution 1

Try changing the format string I to Iw where w is a positive number. Same with E, only use Ew.d.
For explanation see, for example, this link: http://www.cs.mtu.edu/~shene/COURSES/cs201/NOTES/chap05/format.html

Beware though: using, say, I3 for writing out 1234 might print ***, so make sure your formats are wide enough.

EDIT: See @M.S.B.'s answer on how to avoid problems with integer formats.

Solution 2

As already answered, you need to specify widths. Something like ES14.5 might work well for the floating point format. There is a short cut for the integer format: I0 will cause the compiler to use the number of digits needed.