Polymorphic object fail when arrays are passed with arbitrary index range

Question

I provide an example when converting a string to an integer array. I pass an array using an index range.The offset is being initiated by 0 rather than one, so the values in the array are being shifted.

s = "1,2,3,5,8"

Call str_to_num_tu (s, ",", tu(1:8))
$ Output: 
$ tu(1):   0 ; tu(2):   1 ; tu(3):   2

Call str_to_num_tu (s, ",", tu)
$ Output:
$ tu(i):   1 ; tu(2):   2 ; tu(3):   3

Here is my subroutine using an unlimited polymorphic variable.

Subroutine str_to_num_tu   &
  (                        &
    s, dl, tu, pos         &
  )  

Class(*), Intent (InOut) :: tu(:)

Character (len=*), Intent (In) :: s, dl
Character (len=*), Intent (In), Optional :: pos

Integer, Allocatable :: ipos(:)
Integer :: nf, npos, ip, i, j, k

 !!$ Sets tu. 
 !!$ s = "Pablo/Neruda"; tu = ["Pablo","Neruda"] 
 !!$ s = "0.2/1.3/1.5"; tu = [0.2,1.3,1.5] 
 nf = nfields (s, dl)

 Write (*,*) ""
 Write (*,*) "nf: ", nf, "; Size(tu): ", Size(tu)

     i = 1
     Do k = 1, nf-1
       j = Index (s(i:), dl)

       Select Type (tu)
       Type Is (Integer (Int32))
         Call str_to_num (s(i:i+j-2), tu(k))
         Write (*,*) Trim (s(i:))
         Write (*,*) "k: ",  k, "; tu(k): ", tu(k)
       End Select    !!$ tu 

       i = i + j

     End Do

     !!$ Gets last field.
     j = Index (s, dl, back=.true.)
     Write (*,*) "j:", j, "; nf:", nf 

     Select Type (tu)
     Type Is (Integer (Int32))
       Call str_to_num (s(j+1:), tu(nf))
     End Select    !!$ tu 

End Subroutine str_to_num_tu

You do know that even a list-directed internal read of the string will get the integers into an array for you, don't you ? — High Performance Mark
– High Performance Mark, Commented Feb 6, 2015 at 7:04
Can confirm it is a gcc problem when using array ranges into a polymorphic objects. A problem with the offset being 0 rather than 1. — Zeus
– Zeus, Commented Feb 6, 2015 at 13:01
@HighPerformanceMark. Can you elaborate on list-directed internal read please. — Zeus
– Zeus, Commented Feb 6, 2015 at 14:15
If you want to claim there is a fundamental "problem" with gcc please provide a complete and preferably minimal example. — agentp
– agentp, Commented Feb 6, 2015 at 15:51

High Performance Mark · Accepted Answer · 2015-02-07 14:15:08Z

2

To elaborate on my earlier comment. (I don't have Fortran on this computer so the syntax may be a little wonky.) What I meant is that something like this

integer, dimension(6), allocatable :: arr
integer :: ios
character(len=:), allocatable :: str
...
arr = 0
str = "1,2,3,5,8"
read(str,*,iostat=ios) arr

will read the first 6 integers from str into the elements of arr. As it happens str only has 5 integers so the last element of arr is left as 0. iostat is necessary here because an attempt to read more integers than str provides will otherwise produce an end-of-file error at run time.

Of course, this approach generalises to reals, characters and logicals too. Fortran has, built-in, polymorphic reading of intrinsic types. Up to a point.

Fortran will recognise blanks and spaces as value-separators (the Fortran standard uses the word delimiter to mean something else). Note that by setting the decimal mode on an i/o statement to comma Fortran will recognise the comma as a decimal point and treat a semi-colon, ;, as a value-separator. Technically a slash is also a value-separator but it also causes termination of list-directed input of the record so doesn't really act like a value-separator.

If concerned about strings containing other value-separators I might write a function which took a string containing such, returned one with only whitespace, and then perform the internal read on that.

edited Feb 7, 2015 at 14:15

answered Feb 6, 2015 at 15:14

High Performance Mark

78.7k7 gold badges109 silver badges168 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Zeus Over a year ago

How does fortran define the delimiter?

agentp Over a year ago

fair point, if you want to handle arbitrary delimiters you would likely end up with something like your original approach.

Collectives™ on Stack Overflow

Polymorphic object fail when arrays are passed with arbitrary index range

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related