How to read data from various files of different sizes in fortran

[SAMANDEEP]

In my Fortran program, I want to read data from various files whose size I do not know in prior. The input files which I am trying to read may contain different number of entries. If I have same and known number of entries in all files (say 386), I can use something like:


open(unit=1,file='mu.dat',status='old')

open(unit=2,file='md.dat',status='old')

open(unit=3,file='ms.dat',status='old')

do i=1,386,1
read(1,*)mu(i)
read(2,*)md(i)

Can someone please help me in doing it if I don't know the number of rows in my data files in prior?

Thanks,
Saman.

 

[mathman]

Is there some sort of marker to tell the code that the end of file has been reached?

 

[jtbell]

Use an IOSTAT clause in your READ statement to store the read status (which indicates when you have reached the end of file) into a variable; then test that variable to decide whether to exit your input-loop.

http://www.cs.mtu.edu/~shene/COURSES/cs201/NOTES/chap04/iostatus.html

Just as a matter of personal taste, I think the if-statement nested inside the do-loop is a bit clunky, in the examples on that page. Here's how I'd do the second example (reading from a file on unit 4, instead of from *):

open (unit=4, file='mydata.dat', status='old')
sum = 0

read (4, *, iostat=io) x
do while (io == 0)
    sum = sum + x
    read (4, *, iostat=io) x
end do

if (io > 0) then
    write (*, *) 'Check your data file.  Something was wrong.'
else
    write (*, *) 'The total is ', sum
end if

Or you can use an EXIT to get out of the loop, then you need only one READ statement:

do
    read (4, *, iostat=io) x
    if (io /= 0) exit
    sum = sum + x
end do