How to remove leading space when printing with write?

Question

Suppose I have the following code

program fortran
  open(900, FILE='SOMETHING')   
  write(900, *) '21'    
end program fortran

The file form will be

 21

that is, there is a space before the number. How to get rid of that space?

Windowsill

In general, if you want control over formatting, you have to use formatted output, rather than unformatted/default formatting (eg, *). – Ordain

Questions about list-directed IO not having the desired output are common. As already answered, use formatted IO instead. – Are

Answer 1

You can write it as a string:

PROGRAM fortran 

  OPEN(900,FILE='SOMETHING')
  WRITE(900,'(a)') '21'

END PROGRAM FORTRAN

> cat SOMETHING 
21

---

To respond to the comment:

The more explicit way of doing that would be to write the number into a string (you could also use list-directed I/O for this step), remove whitespaces from the string trim and finally output the left-adjusted adjustl:

program test
  character(len=23) :: str

  write(str,'(ES23.15 E3)') 1.23d0
  write(*,'(a)') adjustl(trim(str))

  write(str,'(ES14.7 E2)') 0.12e0
  write(*,'(a)') adjustl(trim(str))
end program

> ./a.out 
1.230000000000000E+000 
1.2000000E-01

This solution is probably more complicated then necessary, but it is a very flexible approach that can be extended easily for arbitrary purposes and formats.

Uball

I want to remove the leading space in real values also. – Windowsill

us a zero field width, eg. write(*,'(f0.4)')3.14 – Luganda

Answer 2

In list-directed format (the * in write(unit,*)) the compiler typically inserts a leading space. The first column used to be used to control line printers but that is now deleted from Fortran.

You can use any explicit format you want to get rid of the leading space. For example the general g0 one or the string specific a or the integer-specific i.

Haircut