Checking for zero data entry

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1

This must be a stupid question, sorry, but I couldn’t find a way to check for just pressing return, and not entering anything, which I don’t want. Checking for entry == “”, for status, and strlen, didn’t do the trick.

3

This code distingushes between nonspace strings and strings with only spaces (i.e. blanks in fortran terms) in them, but it does not distinguish between a <cr> and one or more spaces followed by the <cr>. That is probably sufficient to answer the original question, but I’m wondering if there is a way to use BLANK= somehow to distinguish also between a <cr> and the lines with various numbers of spaces.

4

Thank you for your code, I tried it, entering return does not terminate the program. This is what I did, following your advice:
do
read(*,‘(A)’) seek
if (len_trim(seek) /= 0) exit
end do

5

Hi Ron, so what is the way to terminate execution if only return is pressed?

6

Try this slight modification of @kargl 's code

program foo
   implicit none
   character(len=80) str
   read(*,'(a)') str
   if (len_trim(str) /= 0) then
       print *, 'valid input, str: ',trim(str),', len_trim(str): ',len_trim(str)
   else
       print *, 'empty str, exiting...'
   end if
end program foo
7

Yes - your code does the job. Thank you both.
read(,‘(a)’) seek
if (len_trim(seek) == 0) then
call locate(4,3)
print,“Press Enter to leave.”
read*
stop
end if

1 Like
8

I think the question of how to distinguish between a null line and a line composed of blanks was not addressed; although it is unusual to distinguish between them. One way is the SIZE= parameter

program foo
implicit none
character(len=80) str
integer :: isz, iostat
   do
      write (*, '(a)', advance='no') 'enter value ..'
      read (*, '(a)', size=isz, advance='no', iostat=iostat) str
      if ( str =/ '' ) then
         print *, 'valid input, str: ', trim(str), ', len_trim(str): ', len_trim(str), 'size=', isz
      elseif (isz .eq. 0) then
         print *, 'null str, exiting...'
         stop
      else
         print *, 'blank string, size...', isz
      end if
   end do
end program foo
1 Like