How to read data from a file in fortran

Question

I have a .dat file with a series of data in many rows as shown bellow. I want to read two numbers from each row (2nd and 3rd number) and assign it to variables, such that the 2nd to x(1, i) and 3rd to x(2, i). The value of i changes from 1 to 9000 corresponding to each, 9000 rows in total.

  1   0.2077742E-01   0.1315710E-01   0.2218703E-04  -0.7526844E-05
  2   0.2064923E-01   0.1370921E-01   0.5160497E-05  -0.6106872E-04
  3   0.2069335E-01   0.1446493E-01  -0.1517477E-04  -0.2678836E-04
  4   0.2136012E-01   0.1310226E-01   0.8096579E-04  -0.2091828E-04
  5   0.2129221E-01   0.1380866E-01   0.9713367E-05  -0.2111076E-04
  6   0.2130786E-01   0.1449554E-01  -0.1372658E-05  -0.1607569E-05
  7   0.2195375E-01   0.1304382E-01   0.1206853E-03  -0.2769564E-04
  8   0.2171398E-01   0.1372358E-01  -0.1436741E-04  -0.2231794E-04
  9   0.2193212E-01   0.1446982E-01  -0.5678712E-05  -0.1880452E-04
 10   0.2255034E-01   0.1298457E-01   0.2226397E-03  -0.4775016E-04
 11   0.2234811E-01   0.1370892E-01   0.1539219E-04  -0.2676827E-04
 12   0.2250139E-01   0.1449063E-01   0.6857453E-05  -0.1959816E-04
 13   0.2311584E-01   0.1292939E-01   0.3245234E-03  -0.2145422E-04
 14   0.2265567E-01   0.1367124E-01  -0.5482677E-04  -0.6929516E-04
 15   0.2308732E-01   0.1441105E-01  -0.4883980E-04  -0.5488964E-04
 16   0.2369612E-01   0.1286988E-01   0.3164438E-03   0.5181705E-05
 17   0.2333626E-01   0.1358709E-01   0.2992323E-04  -0.3658970E-04
 18   0.2351967E-01   0.1444346E-01   0.2000859E-04   0.5844122E-05
 19   0.2425562E-01   0.1280576E-01   0.1712960E-03   0.3221714E-04
 20   0.2358314E-01   0.1359597E-01  -0.5286794E-04   0.5639317E-04
 21   0.2406372E-01   0.1434354E-01  -0.3155423E-04   0.2389453E-04
 22   0.2440915E-01   0.1444667E-01   0.9195025E-04   0.2545742E-04
 23   0.2484257E-01   0.1274295E-01   0.6371955E-04   0.1572621E-04
 24   0.2444211E-01   0.1359181E-01  -0.1755666E-03   0.1667949E-03
 25   0.2431473E-01   0.1346151E-01   0.1424003E-03  -0.1036167E-03
 26   0.2498710E-01   0.1434537E-01   0.3143868E-04  -0.4613371E-05
 27   0.2542195E-01   0.1267686E-01  -0.1103745E-04  -0.3899099E-05
 28   0.2527807E-01   0.1340544E-01  -0.1526311E-03  -0.1358241E-04
 29   0.2519788E-01   0.1350556E-01   0.1004352E-03   0.6685333E-04
 30   0.2528750E-01   0.1443648E-01   0.1048803E-03   0.2594530E-04
 31   0.2605581E-01   0.1262580E-01   0.3114293E-04   0.5790992E-05
 32   0.2602784E-01   0.1324524E-01  -0.6518681E-05  -0.1118536E-03
 33   0.2583167E-01   0.1405316E-01  -0.9194989E-05   0.5246043E-04
 34   0.2599337E-01   0.1449096E-01   0.1606246E-03   0.2065522E-04
 35   0.2665012E-01   0.1256468E-01   0.4131713E-04   0.8817949E-05
 36   0.2623754E-01   0.1339113E-01  -0.1785680E-03   0.1278207E-03

I wrote a code as shown bellow, but its not doing what I expected.

I don't know the meaning of each part of this code, such as STATUS='OLD', the meaning * in read command. I just followed some tutorial and trying to code similarly. If possible please explain them as well or refer me to a good, easy and comprehensive book or tutorial.

implicit none
integer:: i,a
real(8):: x(2,9000)

open (2, file="f_xv0950.dat",STATUS='OLD')
    do i=1,9000
        read (2,*) a, x(1,i), x(2,i)
   enddo
close(2)

The outcome that I expect should look like,

x(1,1) = 0.2077742E-01    x(2,1) = 0.1315710E-01
x(1,2) = 0.2064923E-01    x(2,2) = 0.1370921E-01
x(1,3) = 0.2069335E-01    x(2,3) = 0.1446493E-01

and so on....

Your help is much appreciated. Thanks.

!!!!!!!!!!!! Edit_1 !!!!!!!!!!! Added the following lines to write the output to a file with the following code,

open (3,file="tempout.dat") 
    do i=1,9000
         write (2,100) x(1,i), x(2,i) 
    enddo 
100   format(2(2x, e14.7)) 
close (3)

But I am getting an error as

forrtl: severe (24): end-of-file during read, unit 2, file C:\Users\mkha0038\Desktop\XDSPH_RMC_T\f_xv0950.dat

Can you please help.

Possible duplicate of [Reading input files in FORTRAN](https://stackoverflow.com/questions/2813502/reading-input-files-in-fortran) — jbdv, Apr 25 '19 at 08:20
What do you get instead of the expected output? Note that there's an `end do` missing from the small fragment you provide. For much more help, you should consider providing a [mcve]. — francescalus, Apr 25 '19 at 08:25
Regarding your edit, it looks as if you open file unit 3, but write to 2? — jbdv, Apr 26 '19 at 05:39
Thank you @jbdv, that was a good pick. I ruined my input file by writing to it and hence couldn't read again from it. — K.M.Muha, Apr 27 '19 at 01:13

score 0 · Accepted Answer · answered Apr 25 '19 at 12:20

0

What you have written will almost work. Aside from the missing end do, you need to explicitly declare the variable x so that it is dimensioned as an array. Here is an example that works with your truncated example file with 36 lines:

program readin

  real, dimension(2,36) :: x
  integer :: i

  open (2, file="f_xv0950.dat",STATUS='OLD')
  do i=1,36
     read (2,*) a, x(1,i), x(2,i)
  end do
  close(2)

  do i=1,3
     write(6,'(a,i1,a,e13.7,a,i1,a,e13.7)') "x(1,",i,") = ",x(1,i), &
          " x(2,",i,") = ",x(2,i)
  end do

end program readin

It gives output of

x(1,1) = 0.2077742E-01 x(2,1) = 0.1315710E-01
x(1,2) = 0.2064923E-01 x(2,2) = 0.1370921E-01
x(1,3) = 0.2069335E-01 x(2,3) = 0.1446493E-01

as you wish

answered Apr 25 '19 at 12:20

Paul Stevenson

38
5

Why do you think the original `x` isn't declared as an array? If it isn't, (unless it's a function with pointer result - which is exceptionally unlikely), the compiler wouldn't be accepting the program. – francescalus Apr 25 '19 at 12:29
@Paul Stevenson, I have included enddo in the code and added the following lines to write the output to a file, ```open (3,file="tempout.dat") do i=1,9296 write (2,100) x(1,i), x(2,i) enddo 100 format(2(2x, e14.7)) close (3)``` But I am getting an error as "forrtl: severe (24): end-of-file during read, unit 2, file C:\Users\mkha0038\Desktop\XDSPH_RMC_T\f_xv0950.dat". Can you please help. – K.M.Muha Apr 26 '19 at 01:58
That sounds like there aren't 9000 lines in the file. Or perhaps the 9000th line needs a newline character at the end? – Paul Stevenson Jun 27 '19 at 10:11

How to read data from a file in fortran

1 Answers1