Skip a line from text file in Fortran90

Question

I'm writing in fortran (90). My program must read file1, do something with every line of it and write result to file2. But the problem - file1 has some unneeded information in first line.

How can I skip a line from input file using Fortran?

The code:

open (18, file='m3dv.dat')
open (19, file='m3dv2.dat')
do
  read(18,*) x
  tmp = sqrt(x**2 + 1)
  write(19, *) tmp
end do

First line is a combination of text and numbers.

Simon · Accepted Answer · 2022-11-04T07:22:51.160

15

One possible solution has already been presented to you which uses a "dummy variable", but I just wanted to add that you don't even need a dummy variable, just a blank read statement before entering the loop is enough:

open(18, file='m3dv.dat')
read(18,*)
do
    ...

The other answers are correct but this can improve conciseness and (thus) readability of your code.

edited Nov 04 '22 at 07:22

answered Apr 11 '11 at 21:16

Simon

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Thanks, I hadn't realized that. – jonsca Apr 12 '11 at 09:42
2

@osgx Yes. If you want to skip 3 lines, write it three times. – Simon Apr 12 '11 at 17:43
This is brilliant! – Mohamed Jan 29 '22 at 16:19
I do not see any dummy variable in the question's body. I see one variable called `x`, which is then entered into a formula in the next line, so how could it be a "dummy" variable? – Nike Nov 04 '22 at 01:05
Right, it was referring to that first answer at the time. I approved your suggested edit, thanks for the cleanup! – Simon Nov 04 '22 at 07:21

jonsca · Answer 2 · 2011-04-10T12:51:53.170

1

Perform a read operation before the do loop that reads whatever is on the first line into a "dummy" variable.

program linereadtest
implicit none
character (LEN=75) ::firstline
integer :: temp,n
    !
    !
    !
open(18,file='linereadtest.txt')
read(18,*) firstline
do n=1,4
   read(18,'(i3)') temp
   write(*,*) temp
end do
stop
end program linereadtest

Datafile:

This is a test of 1000 things that 10 of which do not exist
50
100
34
566

!ignore the space in between the line and the numbers, I can't get it to format

edited Apr 10 '11 at 12:51

answered Apr 10 '11 at 12:24

jonsca

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how can I read `whatever` in fortran? First line have several space-separated strings and numbers. – osgx Apr 10 '11 at 12:37
1

Make a character array (LEN=100, or whatever). I believe `read` should read until the end of the line. – jonsca Apr 10 '11 at 12:39

score 0 · Answer 3 · answered Apr 10 '11 at 12:23

0

open (18, file='m3dv.dat')
open (19, file='m3dv2.dat')
read(18,*) x // <---

do
  read(18,*) x
  tmp = sqrt(x**2 + 1)
  write(19, *) tmp
end do

The line added just reads the first line and then overwrites it with the seconde on the first iteration.

answered Apr 10 '11 at 12:23

iehrlich

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I think yours assumes the information on the first line of the file is of the same type as the second line. – jonsca Apr 10 '11 at 12:29
@jonsca: yes, I do assume, unless other claimed. – iehrlich Apr 10 '11 at 12:35
No, first line is not a single number, but a combination of numbers and texts – osgx Apr 10 '11 at 12:35
So you'd probably be better off reading the top line into a char array of appropriate length, otherwise you'll get a runtime error, I believe (assuming from line 2 on down are `integers` or `double precision`, etc.) – jonsca Apr 10 '11 at 12:37
yes (`string number string number`), but universal solution is welcome too. – osgx Apr 10 '11 at 12:39
@osgx: the universal solution is to read chars one by one in a loop intil you encounter '\0' char. There also can be a procedure which do this, sorta GetString() in C. – iehrlich Apr 10 '11 at 12:40
1

@suddnely_me there is no '\0' in Fortan – jonsca Apr 10 '11 at 12:52

Skip a line from text file in Fortran90

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