How can I read the number of lines in Fortran 90 from a text file?

Question

How can I read the number of lines present in a text file?

My text file seems to be like:

1
2
3
.
.
.
n

score 23 · Answer 1 · edited Dec 10 '21 at 21:13

23

Use:

nlines = 0
OPEN (1, file = 'file.txt')
DO
    READ (1,*, END=10)
    nlines = nlines + 1
END DO
10 CLOSE (1)

print*, nlines

end

Or:

nlines = 0
OPEN (1, file = 'file.txt')
DO
  READ(1,*,iostat=io)
  IF (io/=0) EXIT
  nlines = nlines + 1
END DO
CLOSE (1)

print*, nlines

edited Dec 10 '21 at 21:13

Peter Mortensen

30,738
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answered Nov 22 '16 at 12:01

prograils

2,248
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2

You may need to declare `io` as an integer. – jsta Feb 14 '18 at 21:09

score 2 · Answer 2 · edited Dec 10 '21 at 21:11

Although it is unclear, I think if you just have to know the number lines in the files, just use wc -l <filename> on the command line.

If you want to do anything further, just read the number of lines in a character string and count until the end of file is encountered. Here is the code below:

character :: inputline*200

OPEN(lin, file=inputfile, status='old', action='read', position='rewind')

loop1: DO
   READ(lin,*,iostat=eastat) inputline
   IF (eastat < 0) THEN
    numvalues = numvalues + 1
WRITE(*,*) trim(inputfile), ' :number of records =', numvalues-1
EXIT loop1

ELSE IF (eastat > 0) THEN
    STOP 'IO-error'
ENDIF
    numvalues = numvalues + 1

END DO loop1

With the Fortran approach you don't even need to actually transfer anything. — francescalus, Jun 08 '15 at 14:23

How can I read the number of lines in Fortran 90 from a text file?

2 Answers2

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