notabs Subroutine

public impure elemental subroutine notabs(instr, outstr, ilen)


notabs(3f) - [fpm_strings:NONALPHA] expand tab characters (LICENSE:PD)


subroutine notabs(INSTR,OUTSTR,ILEN)

 character(len=*),intent=(in)  :: INSTR
 character(len=*),intent=(out) :: OUTSTR
 integer,intent=(out)          :: ILEN


NOTABS() converts tabs in INSTR to spaces in OUTSTR while maintaining columns. It assumes a tab is set every 8 characters. Trailing spaces are removed.

In addition, trailing carriage returns and line feeds are removed (they are usually a problem created by going to and from MSWindows).

What are some reasons for removing tab characters from an input line? Some Fortran compilers have problems with tabs, as tabs are not part of the Fortran character set. Some editors and printers will have problems with tabs. It is often useful to expand tabs in input files to simplify further processing such as tokenizing an input line.


 instr     Input line to remove tabs from


 outstr    Output string with tabs expanded. Assumed to be of sufficient
 ilen      Significant length of returned string


Sample program:

program demo_notabs

!  test filter to remove tabs and trailing white space from input
!  on files up to 1024 characters wide
use fpm_strings, only : notabs
character(len=1024) :: in,out
integer             :: ios,iout
      if(ios /= 0) exit
      call notabs(in,out,iout)
end program demo_notabs


GNU/Unix commands expand(1) and unexpand(1)


Type IntentOptional Attributes Name
character(len=*), intent(in) :: instr
character(len=*), intent(out) :: outstr
integer, intent(out) :: ilen


Source Code

Source Code

elemental impure subroutine notabs(instr,outstr,ilen)

! ident_31="@(#)fpm_strings::notabs(3f): convert tabs to spaces while maintaining columns, remove CRLF chars"

character(len=*),intent(in)   :: instr        ! input line to scan for tab characters
character(len=*),intent(out)  :: outstr       ! tab-expanded version of INSTR produced
integer,intent(out)           :: ilen         ! column position of last character put into output string
                                              ! that is, ILEN holds the position of the last non-blank character in OUTSTR

integer,parameter             :: tabsize=8    ! assume a tab stop is set every 8th column
integer                       :: ipos         ! position in OUTSTR to put next character of INSTR
integer                       :: lenin        ! length of input string trimmed of trailing spaces
integer                       :: lenout       ! number of characters output string can hold
integer                       :: istep        ! counter that advances thru input string INSTR one character at a time
character(len=1)              :: c            ! character in input line being processed
integer                       :: iade         ! ADE (ASCII Decimal Equivalent) of character being tested

   ipos=1                                     ! where to put next character in output string OUTSTR
   lenin=len_trim(instr( 1:len(instr) ))      ! length of INSTR trimmed of trailing spaces
   lenout=len(outstr)                         ! number of characters output string OUTSTR can hold
   outstr=" "                                 ! this SHOULD blank-fill string, a buggy machine required a loop to set all characters

      SCAN_LINE: do istep=1,lenin             ! look through input string one character at a time
         c=instr(istep:istep)                 ! get next character
         iade=ichar(c)                        ! get ADE of the character
         EXPAND_TABS : select case (iade)     ! take different actions depending on which character was found
         case(9)                              ! test if character is a tab and move pointer out to appropriate column
            ipos = ipos + (tabsize - (mod(ipos-1,tabsize)))
         case(10,13)                          ! convert carriage-return and new-line to space ,typically to handle DOS-format files
         case default                         ! c is anything else other than a tab,newline,or return  insert it in output string
            if(ipos > lenout)then
               write(stderr,*)"*notabs* output string overflow"
         end select EXPAND_TABS
      enddo SCAN_LINE

      ipos=min(ipos,lenout)                   ! tabs or newline or return characters or last character might have gone too far
      ilen=len_trim(outstr(:ipos))            ! trim trailing spaces

end subroutine notabs