Read CHARACTER string without knowing the length

Question

I have to read input data in my Fortran 77 program. It Looks as following

FILENAME PATH

temperature  ./Data

and then in the Fortran code I proceed as following

CHARACTER*8 FILENAME,PATH

READ(5,'(A80)') CARDIN 

READ(5,*) FILENAME,PATH

but the problem is that I don't know the length of FILENAME and PATH in advance. So what if the user doesn't give names that are not exactly 8? Do you have any idea how I can solve this?

Do you truly have a requirement to use/be restricted by Fortran 77? — francescalus
– francescalus, Commented Nov 16, 2016 at 9:17
Be aware of problems like this one when reading file paths (containing unquoted slashes) with list-directed input. — francescalus
– francescalus, Commented Nov 16, 2016 at 11:22
I suggest you read the ISO standard documentation for FORTRAN 77 on Hollerith constants or how assumed-size arrays apply to character types. I don't know of any way to achieve your goal without resorting to features from newer Fortran standards. — jlokimlin
– jlokimlin, Commented Nov 17, 2016 at 18:20

Holmz · Accepted Answer · 2016-11-16 11:41:37Z

1

One can do it in F77, but this is more F90 in style.

INTEGER*4 FUNCTION LengthString(String)
IMPLICIT NONE
CHARACTER* String
INTEGER*4 I

LengthString = -1 !default is -1 just because.

DO I=LEN(String), 1, -1
  IF(String(I:I) .ne. ' ') THEN
     LengthString = I
     EXIT
  ENDIF
ENDDO

RETURN
END FUNCTION LengthString

And the program could be something like this:

PROGRAM Main
CHARACTER*80 AA
INTEGER*4 LenAA
...
LenAA = LengthString(AA)
IF(LenAA .lt. 1) !error out
...
WRITE(*,10) LenAA, A(1:LenAA)
10 FORMAT('AA(',I4,')="',A,'"')
...

Open statement could look like this:

OPEN(FILE=AA(1:LenAA),...

And the path is the same deal.

NewLongFile = Path(1:LenPath) // '/' // AA(1:LenAA)
Len_NewLongFile = LengthString(NewLongFile)

answered Nov 16, 2016 at 11:41

Holmz

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4 Comments

francescalus Over a year ago

What is objectionable about len_trim?

Holmz Over a year ago

i see what you mean @francescalus ! I had rolled my own a long time ago... [strokes beard -n- chins]

francescalus Over a year ago

To be fair, len_trim isn't F77 (but then, neither is enddo).

jlokimlin Over a year ago

Your code does the job but does not answer the original question. @MorganeMaPh explicitly said that he/she must restrict themselves to FORTRAN 77. implicit none, len_trim for character manipulation, end do loop termination, and the exit statement were introduced in Fortran 90/95. Never mind the 6 character length restriction for naming conventions.

PeMa · Accepted Answer · 2016-11-16 10:55:29Z

0

I'm not entirely sure what you want to do, but you can use TRIM to "cut" the blanc space:

      Program TEST
      CHARACTER*50 FILENAME,PATH

      READ(*,*) FILENAME,PATH
      WRITE(*,*)TRIM(FILENAME),TRIM(PATH)
      END

answered Nov 16, 2016 at 10:55

PeMa

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5 Comments

Holmz Over a year ago

Nice use of TRIM. I usually use 80, 128, 256, or 1024. And then a seperate variable to understand the length. You will quickly find a function to find the end of the string can be useful even if you also use TRIM. And useful for a variety of flexible output handling of strings.

MorganeMaPh Over a year ago

Thank you @PeMa could work... What I would like to do is write a Statement like "Read the string until you get a blanc space".

Vladimir F Героям слава Over a year ago

The problem is not in writing, but in reading. This is not a good solution.

MorganeMaPh Over a year ago

Exactly @VladimirF ... also as I defined the variable I already have to give a length... this is bad

IanH Over a year ago

TRIM is not Fortran 77.

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