backspace error (reading file from the end)

Hi, everybody,

I have the following question.

I need to read the last several lines
of a very big file with columns of numbers.
(I do not want to read the whole file,
just last several lines)

So, I wrote a subroutine that should do
this for me (see code further).
It reads the last line without a problem.
But when I ask it to read second or third
line from the end, it crashes with error
message

forrtl: severe (23): BACKSPACE error, unit 10, file ...

It should be something obvious, but I do not see what
is wrong. I thought when I use backspace twice I
should be at the position to read the second line
from the end. But instead I get the error.
How do you, people, read files from the end?
Thank you for any suggestions.

program test1
implicit none

integer, parameter :: dp = kind(1.0d0)
character(len=9) :: filename
real(kind=DP) :: line2_i(4)
real(kind=DP) :: line1_i(4)

filename="test.data"

line2_i(1)=tail_read(filename,eline=2,line_size=4,element=1)
line2_i(2)=tail_read(filename,eline=2,line_size=4,element=2)
line2_i(3)=tail_read(filename,eline=2,line_size=4,element=3)
line2_i(4)=tail_read(filename,eline=2,line_size=4,element=4)


print*,'line2=',line2_i


contains

function tail_read(filename,eline,line_size,element) result(arg_out)

implicit none

character(len=*) :: filename
integer, intent(in) :: eline ! number of line from the end
integer, intent(in) :: line_size ! total number of columns
integer, intent(in) :: element ! column to read

real(kind=DP) :: arg_out

integer :: counter
integer :: iocheck

real(kind=DP) :: rarray(line_size)

open(10,file=filename,status='old',mode='read',&
& access='sequential',position='append',iostat=iocheck)

if(iocheck .ne. 0)stop 'STOP! ERROR IN TAIL_READ'

do counter=1,eline
backspace(10)
end do

read(10,fmt=*) rarray

close(10)

arg_out=rarray(element)


end function tail_read

end program test1

















--
Igor R.
.

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