Fortran: can’t get no leading zero


Perhaps someone who eats Fortran for breakfast can help me.

Is it really the case that there’s no way (in (portable) Fortran) to format a floating point number so that it has as many leading zeros as are necessary to fill the field?

Imagine I wanted to output something like ISO 6709 and have the location of Sheffield displayed as:


In Python (using C’s syntax) this is just '%+06.2f%+07.2f' % (lat,lon).

Can I really not do this in Fortran? Surely I have just missed something.


gives me:

+53.40 -1.50

which is not what I wanted at all. I (half humourously) tried F06.2,F07.2 but that doesn’t work.

If true, it’s absolutely unforgivable.

22 Responses to “Fortran: can’t get no leading zero”

  1. Nick Barnes Says:


  2. drj11 Says:

    Yeah. Tried that. NBG. Apparently that only does anything useful for input.

  3. Nick Barnes Says:
    It looks as if you can prefill the output field with zeroes and then go back and write the number over it. Something like 6’0′,TL6,F6.2

  4. Gareth Rees Says:

    Presumably you figured out how to do this anyway, right?

    WRITE (*,'(SP,i3.2,SS,f3.2,SP,i4.3,SS,f3.2)’) FLOOR(LAT), (LAT – FLOOR(LAT)), FLOOR(LON), (LON – FLOOR(LON))

  5. Gareth Rees Says:

    Oops: that only handles positive values of LAT and LON. So maybe something like

    WRITE (*,'(SP,i3.2,SS,f3.2,SP,i4.3,SS,f3.2)’) FLOOR(AINT(LAT)), ABS(LAT – AINT(LAT)), FLOOR(AINT(LON)), ABS((LON – AINT(LON)))

  6. Gareth Rees Says:

    No, that doesn’t work for values with modulus less than 1.

    OK, I have no idea how to do this in just one WRITE statement.

  7. Gareth Rees Says:

    So how about this (X is a dummy REAL variable needed for the SIGN procedure to work):

    WRITE (*,'(SP,f3.0,TL2,SS,i2.2,f3.2,SP,f3.0,TL2,SS,i3.3,f3.2)’) &

  8. Gareth Rees Says:

    Not sure that was worth forty minutes’ effort.

  9. Nick Barnes Says:

    Hmm. I posted a reply here but it doesn’t seem to have appeared. You can pre-fill the field with zeroes and then use TL to go back and write the value.

  10. drj11 Says:

    @Nick: I have recovered your comment from the spam trap.

    I still have to get the sign right and in the right place, but clearly I can do that with more TLing. Gak.

  11. drj11 Says:

    Bottom line: I didn’t miss an easy fix.

  12. Gareth Rees Says:

    When I try Nick’s recipe, it doesn’t work because the spaces generated by the F output control overwrite the zeros. For example, when I run this statement in GNU Fortran 4.4.0:

    WRITE (*,”(‘000000’,TL5,f6.2)”) -45.2

    I get the output:


    (Hence my recipe of 2008-08-30 at 11:37:40, which outputs the sign, integer part, and fractional part in separate controls.)

  13. Gareth Rees Says:

    No, that wasn’t what I meant to write. I meant that the sign goes in the wrong place.

    Not my day today.

  14. Rich Says:

    Ugly but easy:

    program spike
    character title*16
    double precision t


    write(title(1:8),'(f8.2)’) t
    write(title(1:5),'(i5.5)’) nint(t)
    write(*,*) title

    • Oliver A Says:

      Shorter, does the (same) trick in one line:

      t = 3.14159
      write(*,'(F8.2,TL8,I5.5)’) t, nint(t)


      • drj11 Says:

        Funny. But don’t, whatever you do, try it with 2.718. NINT indeed.

        And I’m not just being snarky, this is a genuine problem. I’m not a Fortran expert and I do not know what the correct coercion is.

      • Says:

        Actually, this is the right code (and don’t forget to tab back RIGHT after you’re done):

        t = 3.14159
        write(*,'(F8.5,TL8,I2.2,TR6)’) t, nint(t)

  15. MvdS Says:

    I don’t know an easy fix for floats (unlike integers). In the last comment, replace nint() by floor().

    • drj11 Says:

      Try -2.1. FLOOR indeed. Do I have to debug everone’s Fortran? I don’t even know the language. It’s going on my CV at this rate.

      • dib Says:

        Why not use int(), i.e.

        t = 3.14159
        write(*,’(F8.2,TL8,I5.5)’) t, int(t)

        This should work with numbers of both sign as int() truncates towards zero.

  16. drj11 Says:

    @dib. Ah, very cunning. It so happens that I do not have access to a Fortran compiler right now. So perhaps you can be a good chap and test if it works with t = 1.997.


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