Getting fortran runtime error: end of file - runtime

Question

I have recently learned how to work with basic files in Fortran
and I assumed it was as simple as:
open(unit=10,file="data.dat")
read(10,*) some_variable, somevar2
close(10)
So I can't understand why this function I wrote is not working.
It compiles fine but when I run it it prints:
fortran runtime error:end of file
Code:
Function Load_Names()
character(len=30) :: Staff_Name(65)
integer :: i = 1
open(unit=10, file="Staff_Names.txt")
do while(i < 65)
read(10,*) Staff_Name(i)
print*, Staff_Name(i)
i = i + 1
end do
close(10)
end Function Load_Names
I am using Fortran 2008 with gfortran.

Answer 1

A common reason for the error you report is that the program doesn't find the file it is trying to open. Sometimes your assumptions about the directory in which the program looks for files at run-time will be wrong.
Try:
using the err= option in the open statement to write code to deal gracefully with a missing file; without this the program crashes, as you have observed;
or
using the inquire statement to figure out whether the file exists where your program is looking for it.

Answer 2

You can check when a file has ended. It is done with the option IOSTAT for read statement.
Try:
Function Load_Names()
character(len=30) :: Staff_Name(65)
integer :: i = 1
integer :: iostat
open(unit=10, file="Staff_Names.txt")
do while(i < 65)
read(10,*, IOSTAT=iostat) Staff_Name(i)
if( iostat < 0 )then
write(6,'(A)') 'Warning: File containts less than 65 entries'
exit
else if( iostat > 0 )then
write(6,'(A)') 'Error: error reading file'
stop
end if
print*, Staff_Name(i)
i = i + 1
end do
close(10)
end Function Load_Names

Answer 3

Using Fortran 2003 standard, one can do the following to check if the end of file is reached:
use :: iso_fortran_env
character(len=1024) :: line
integer :: u1,stat
open (newunit=u1,action='read',file='input.dat',status='old')
ef: do
read(u1,'A',iostat=stat) line
if (stat == iostat_end) exit ef ! end of file
...
end do ef
close(u1)

Answer 4

Thanks for all your help i did fix the code:
Function Load_Names(Staff_Name(65))!Loads Staff Names
character(len=30) :: Staff_Name(65)
integer :: i = 1
open(unit=10, file="Staff_Names.txt", status='old', action='read')!opens file for reading
do while(i < 66)!Sets Set_Name() equal to the file one string at a time
read(10,*,end=100) Staff_Name(i)
i = i + 1
end do
100 close(10)!closes file
return!returns Value
end Function Load_Names
I needed to change read(10,*) to read(10,*,END=100)
so it knew what to do when it came to the end the file
as it was in a loop I assume.

Answer 5

Then your problem was that your file was a row vector, and it was likely
giving you this error immediately after reading the first element, as #M.S.B. was suggesting.
If you have a file with a NxM matrix and you read it in this way (F77):
DO i=1,N
DO j=1,M
READ(UNIT,*) Matrix(i,j)
ENDDO
ENDDO
it will load the first column of your file in the first row of your matrix and will give you an error as soon as it reaches the end of the file's first column, because the loop enforces it to read further lines and there are no more lines (if N<M when j=N+1 for example). To read the different columns you should use an implicit loop, which is why your solution worked:
DO i=1,N
READ(UNIT,*) (Matrix(i,j), j=1,M)
ENDDO

Answer 6

I am using GNU Fortran 5.4.0 on the Ubuntu system 16.04. Please check your file if it is the right one you are looking for, because sometimes files of the same name are confusing, and maybe one of them is blank. As you may check the file path if it is in the same working directory.