Can hidden characters change the name of output files in fortran? - fortran

Question

I'm using a subroutine to output an array gathered from a previous function. After running my program and only calling the subroutine once, my intended file name, testf.txt, is given as "testf.txtÑ #." Thinking it was a hidden character generated by a portion I borrowed from a friend, I retyped the whole section but nothing changed. When I do multiple calls, the names of the the files add onto one another. Intended, "testf.txt" "testg.txt" "testh.txt", given, "testf.txttestg" "testg.txttesth" and "testh.txt". The content is fine, the name being the only issue. Would that be caused by hidden characters in the code, or a logic error in how the subroutine hold information?
Thanks,
Thomas
Main Program
program Main
implicit none
!DATA DICTIONARY
character :: selection ! Method of summation
! L = left Riemann sum
! R = right Riemann sum
! M = Midpoint rule
! T = Trapezoidal rule sum
! S = Simpson's rule
integer :: n ! Number of subintervals the integral is to
! be divided into
integer :: func ! The function to be integrated
! f = (28.0/5) + 2*sin(4*x) - (1/x)
! g = ln(4x) + (19x)^3 - 43
! h = 1/(sqrt(2.0*PI))*exp(-(x**2)/2.0)
character(20) :: filename
real, external :: f
real, external :: g
real, external :: h
real, dimension(1000) :: area
!Declare functions used
real :: Quad
write(*,*) "Written in the form ",
+ "Quad(func, n, left, right, selection):"
write(*,*) " "
!Test Drivers
write(*, *) Quad(f, 10, 0.2, 3.2, 'T', area)
call Out(10, area, 'testf.txt')
write(*, *) Quad(g, 10, 5.0, 10.0, 'L', area)
call Out(10, area, 'testg.txt')
write(*, *) Quad(h, 25, 1.0, 10.0, 'L', area)
call Out(10, area, 'testh.txt')
end program Main
Actual Out subroutine
subroutine Out(n, area, filename)
!PRE: n > 0
! area is the initialized array area(1...n)
! filename is initialized
implicit none
integer, intent(in) :: n
real, dimension(n), intent(in) :: area
character(20), intent(in) :: filename
integer :: i
open(unit=1, file=filename, form='formatted', !Writes area(1...n) to a file
+ action='write', status='replace')
do i = 1, n, 1
write(1,*) area(i)
end do
close(unit=1)
end subroutine Out

Answer 1

This sort of error is normally an indication of one or more of:
Array overruns - i.e. if your data is in an array of size 10 followed by your filen ame in memory and you write to array element 11 it will corrupt the file name.
Array under run - similar to the above but at the start of the array
Parameter corruption - if the text for the file name is passed as a read write parameter then it can be overwritten in the code.
You can often sort out this sort of issue by a) turn on all compiler error checking and fix all the warnings and/or b running the code through a lint equivalent such as ftnchek and fixing the issues it finds.