C Library Functions - notopen (3)

NAME

notopen(3f) - [M_io:QUERY] Find a FUN/LUN (Fortran-unit-number) that is not in use (LICENSE:PD)

Synopsis
Description
Options
Notes
Examples
Author
License

SYNOPSIS

Usage

      integer function notopen(start,end,err)
      integer,optional,intent(in)  :: start
      integer,optional,intent(in)  :: end
      integer,optional,intent(out) :: err

DESCRIPTION

A free FORTRAN unit number is needed to OPEN a file. NOTOPEN() returns a FORTRAN unit number from START to END not currently associated with an I/O unit. START and END are expected to be positive integers where

END >= START.

If NOTOPEN() returns -1, then no free FORTRAN unit could be found in the specified range.
Otherwise, NOTOPEN() returns an integer representing a free FORTRAN logical unit number. Note that NOTOPEN() assumes the following unit numbers defined by the Fortran 2008 ISO_FORTRAN_ENV module
      ERROR_UNIT,INPUT_UNIT,OUTPUT_UNIT
are special, and will never return those values.

OPTIONS

start optional logical unit number to start scan at, defaults to 10.

end optional logical unit number to stop scan at, defaults to 99.

err optional error flag returned. ERR will be non-zero if no errors. If not present and an error occurs the program will stop instead of returning.

NOTES

Why are the default START and END limits from 10 to 99? the Fortran 77 standard did not specify a specific limit on the upper range limit, but the LUN range of 1 to 99 was almost always supported in conventional programming environments. Additionally, units in the range 0-10 have often been the units used for pre-assigned files. Occasionally 100, 101 and 102 are reserved (for files such as standard input, standard output, standard error, ...). Therefore, the defaults for START and END were selected to be 10 and 99. And most programs do not need more than 90 files simultaneously open, so the defaults work well in practice with many versions/vintages of Fortran.
Note that an environment may impose a limit on the number of simultaneously open files (which some compilers work around).
Beginning with f2008, you can probably use OPEN(NEWUNIT=...) instead of an open unit locator.

EXAMPLES

Sample program:

    program demo_notopen ! test the NOTOPEN(3f) function
    use m_io, only: notopen
    implicit none
    integer :: ii, ierr, igot

    write(*,*)’check for preassigned files from unit 0 to unit 1000’
    write(*,*)’(5 and 6 always return -1)’

    do ii=0,1000
       if(notopen(ii,ii,ierr)  /=  ii)then
          write(*,*)’INUSE:’,ii, notopen(ii,ii,ierr)
       endif
    enddo

    ! open all files from UNIT=10 to UNIT=30 so have used units
    do ii=10,30,1
      open(unit=ii,status="scratch")
    enddo
    ! close UNIT=25
    close(25)

    ! find open file in range 10 to 30
    write(*,*)’Should get 25 for this ..’,notopen(10,30,ierr)

    close(18)
    do ii=10,32
      igot=notopen(ii,ii,ierr)
      write(*,*)’For unit ’,ii,’ I got ’,igot,’ with ERR=’,ierr
    enddo

    end program demo_notopen

Expected output(can vary with each programming environment):

check for preassigned files from unit 0 to unit 1000 (5 and 6 always return -1) INUSE: 0 -1 INUSE: 5 -1 INUSE: 6 -1 Should get 25 for this .. 25 For unit 10 I got -1 with ERR= -1 For unit 11 I got -1 with ERR= -1 For unit 12 I got -1 with ERR= -1 For unit 13 I got -1 with ERR= -1 For unit 14 I got -1 with ERR= -1 For unit 15 I got -1 with ERR= -1 For unit 16 I got -1 with ERR= -1 For unit 17 I got -1 with ERR= -1 For unit 18 I got 18 with ERR= 0 For unit 19 I got -1 with ERR= -1 For unit 20 I got -1 with ERR= -1 For unit 21 I got -1 with ERR= -1 For unit 22 I got -1 with ERR= -1 For unit 23 I got -1 with ERR= -1 For unit 24 I got -1 with ERR= -1 For unit 25 I got 25 with ERR= 0 For unit 26 I got -1 with ERR= -1 For unit 27 I got -1 with ERR= -1 For unit 28 I got -1 with ERR= -1 For unit 29 I got -1 with ERR= -1 For unit 30 I got -1 with ERR= -1 For unit 31 I got 31 with ERR= 0 For unit 32 I got 32 with ERR= 0

AUTHOR

John S. Urban

LICENSE

Public Domain

Nemo Release 3.1

notopen (3)

February 23, 2025

Generated by manServer 1.08 from 5793a709-a6d3-403b-81a2-f94bb423e75c using man macros.

start	optional logical unit number to start scan at, defaults to 10.
end	optional logical unit number to stop scan at, defaults to 99.
err	optional error flag returned. ERR will be non-zero if no errors. If not present and an error occurs the program will stop instead of returning.