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.

Solution 1

You already found the solution 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.

Solution 2

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

Comments

[jonsca]

I think yours assumes the information on the first line of the file is of the same type as the second line.

[iehrlich]

@jonsca: yes, I do assume, unless other claimed.

[osgx]

No, first line is not a single number, but a combination of numbers and texts

[osgx]

how can I read whatever in fortran? First line have several space-separated strings and numbers.

[jonsca]

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.)

[osgx]

yes (string number string number), but universal solution is welcome too.

[jonsca]

Make a character array (LEN=100, or whatever). I believe read should read until the end of the line.

[iehrlich]

@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.

[jonsca]

@suddnely_me there is no '\0' in Fortan

[jonsca]

Thanks, I hadn't realized that.

[Simon]

@osgx Yes. If you want to skip 3 lines, write it three times.

[Mohamed]

This is brilliant!