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From: elijah on 23 Apr 2008 06:08
program main
integer ln
real newval,oldval
ln=178
open(unit=10,file='file.txt',
& status='old',form='FORMATTED',access='sequential')
rewind 10
do n=1,ln-1,1
if(n.eq.ln)then
read(10,20)oldval
endif
enddo
write(*,*)'Old value was'
write(*,20)oldval
do n=1,ln-1,1
if(n.eq.ln)then
write(10,20),newval
endif
enddo
write(*,*)'New value is'
write(*,20)newval
20 format(10x,f10.3)
close(10)
end program

in the above program I would like to modify the columns 11-20 in line
178 of "file.txt". Text file contains lines of different lengths,
character strings, floating point numbers etc.

It seems that I am unable to locate porperly the columns and/or the
line.
Any help will be much appreciated.

regards
MI
From: e p chandler on 23 Apr 2008 07:22
On Apr 23, 6:08 am, elijah <mily...(a)gmail.com> wrote:
>       program main
>          integer ln
>          real    newval,oldval
>          ln=178
>          open(unit=10,file='file.txt',
>      &        status='old',form='FORMATTED',access='sequential')
>          rewind 10
>          do n=1,ln-1,1
>             if(n.eq.ln)then
>                read(10,20)oldval
>             endif
>          enddo
>          write(*,*)'Old value was'
>          write(*,20)oldval
>          do n=1,ln-1,1
>             if(n.eq.ln)then
>                write(10,20),newval
>             endif
>          enddo
>          write(*,*)'New value is'
>          write(*,20)newval
>    20    format(10x,f10.3)
>          close(10)
>       end program

You can not both read and write a sequential file at the same time.
You can read ... modify ... write a direct access file, but this type
of file access requires a fixed record length.

> in the above program I would like to modify the columns 11-20 in line
> 178 of "file.txt". Text file contains lines of different lengths,
> character strings, floating point numbers etc.

1. The usual way to handle this is to use two files. Copy lines as is
from old file to new file. Read the target line, modify it, write it
to the new file. Copy the rest of the source file to the destination
file. Delete the old source file. Rename the destination file.

2. Fortran is not the way I prefer to handle these text modification
tasks. If you only have one line of data to modify, why not use a text
editor and do it manually? Otherwise any one of a number of scripting
languages would be better choices for this task.

3. Without a better idea of what defines a "column", it is difficult
to solve your task.

> It seems that I am unable to locate porperly the columns and/or the
> line.
> Any help will be much appreciated.

4. Search this newsgroup for other postings on this topic. IMO "How do
I modify a data file, in place?" has joined the ranks of the FAQ in
this newsgroup.

-- e

From: elijah on 23 Apr 2008 07:47
> 3. Without a better idea of what defines a "column", it is difficult
> to solve your task.

$# nrcyck drtol drfctr drterm tssfdr irelal
edttl idrflg
250 0.001000 0.995000 0.000 0.000 0 0.040000
*CONTROL_ENERGY
$# hgen rwen slnten rylen
2 2 2 2


this is an excerpt from the file. above is the longest line in the
text file. lines do not have one fixed length. I am considering each
character "space" as one column.
From: Arjen Markus on 23 Apr 2008 07:54
On 23 apr, 12:08, elijah <mily...(a)gmail.com> wrote:
>       program main
>          integer ln
>          real    newval,oldval
>          ln=178
>          open(unit=10,file='file.txt',
>      &        status='old',form='FORMATTED',access='sequential')
>          rewind 10
>          do n=1,ln-1,1
>             if(n.eq.ln)then
>                read(10,20)oldval
>             endif
>          enddo
>          write(*,*)'Old value was'
>          write(*,20)oldval
>          do n=1,ln-1,1
>             if(n.eq.ln)then
>                write(10,20),newval
>             endif
>          enddo
>          write(*,*)'New value is'
>          write(*,20)newval
>    20    format(10x,f10.3)
>          close(10)
>       end program
>
> in the above program I would like to modify the columns 11-20 in line
> 178 of "file.txt". Text file contains lines of different lengths,
> character strings, floating point numbers etc.
>
> It seems that I am unable to locate porperly the columns and/or the
> line.
> Any help will be much appreciated.
>
> regards
> MI

Well, if you use the READ statement like this,
it will simply read a part of the line and then jump to the
next line.

I'd say:

character(len=100) :: line ! Or whatever the length is
! the longest line

do
read( 10, '(a)' ) line
line(11:20) = ... new value ...
write( 20, '(a)' ) line
enddo

(with all manner of details left out)

Regards,

Arjen
From: e p chandler on 23 Apr 2008 08:10
On Apr 23, 7:47 am, elijah <mily...(a)gmail.com> wrote:
> > 3. Without a better idea of what defines a "column", it is difficult
> > to solve your task.
>
> $#  nrcyck     drtol    drfctr    drterm    tssfdr    irelal
> edttl    idrflg
>        250  0.001000  0.995000     0.000     0.000         0  0.040000
> *CONTROL_ENERGY
> $#    hgen      rwen    slnten     rylen
>          2         2         2         2
>
> this is an excerpt from the file. above is the longest line in the
> text file. lines do not have one fixed length. I am considering each
> character "space" as one column.

So you want to replace the contents in print positions 11 to 20 with
something else? Again, you want to over-write the old data with the
new, leaving the length of the original line unchanged?

- e

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