How can I know the length of user input with trailing whitespaces in Fortran?

Question

I want to know the length of one line of the user input in Fortran. Since that input can contain some trailing whitespaces, LEN_TRIM does not give the correct answer.

program test

implicit none
character(len=100) :: s

read(*, '(a)') s
write(*, '(i0)') len_trim(s)

end program test

example inputs and outputs:

input: Hello World!

output: 12

expected output: 15

input: (5 spaces)

output: 0

expected output: 5

Answer 1

Read the input one character at a time and count the number read from STDIN.

program foo
  character(len=100) s
  integer i
  i = 1
  do
      read(*,'(A1)',eor=10,advance='no') s(i:i)
      i = i + 1
  end do
10 print *, i - 1  ! Minus for '\n'
end program foo

TRIM and LEN_TRIM will still get rid of trailing whitespace. You can test that s(i:i) == ' ' and then set it to some printable character.