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stringfortran

Split Fortran character string of unknown length but known substring format by commas?

I'm trying to split an input variable to some Fortran code by commas. The variable is a character string that contains a variable number of dates, but the dates are always in DD-MMM-YYYY format.

An example of such a string:

04-DEC-2015,10-DEC-2015,23-DEC-2015,25-DEC-2015

It's not always four dates, but it is always an 11-character date in that format.

I simply want to print these dates on separate lines; the current code:

write(outfile,10) '     - ', TRIM(days)

Prints:

     -  04-DEC-2015,10-DEC-2015,23-DEC-2015,25-DEC-2015

And I want to write something that prints:

     -  '04-DEC-2015'
     -  '10-DEC-2015'
     -  '23-DEC-2015'
     -  '25-DEC-2015'

Is there a straightforward way to do this (I'm pretty new to Fortran)? I'm thinking counting the number of commas in the string, adding 1 to get the number of dates, and inside a loop creating a CHARACTER(11) variable that fits each date, getting 11 characters from the string at a time (skipping commas), and printing that date in the format I want. Is that too convoluted?

Solution

  • As has previously been suggested, a list-directed read from an internal file will handle the splitting on commas without more effort. For

    character(11) :: split_days(MAX_DAYS)=''
ndays = ...
read(days,*) split_days(1:ndays)

    to work we need to know the value of ndays. If you're happy with something like

    ndays = (len_trim(days)+1)/12
ndays = INDEX(days,',',BACK=.TRUE)/12+1

    or

    ndays = COUNT([(days(i:i),i=1,LEN_DAYS)].eq.',')+1

    then everything is good.

    Alternatively, you could have an allocatable array

    character(11), allocatable :: split_days(:)
ndays = ...
allocate (split_days(ndays))
read(days,*) split_days

    Alternatively, you don't need to read the internal file (list-directed or otherwise), although I probably would if I trusted the form of my input data.

    do i=1,MAX_DAYS
  split_days(i)=days(12*(i-1)+1:)
  if (INDEX(days(12*i:),',').eq.0) exit
end do

    A further possibility with the list-directed read approach is to choose a large number to read, and if that fails, try again reading fewer. This makes sense only in more tricky situations.

    Finally, you can use the usual array shrinking/growing tricks if desired.

    If you're just after printing, not storing, then the loop approach above avoids messing about with an array of unknown length:

    do i=1,MAX_DAYS
  print '("     - ''",A11,"''")', days(12*(i-1)+1:)
  if (INDEX(days(12*i:),',').eq.0) exit
end do