Regarding pointer to an array of items

Reddy__Karunakar · ‎03-20-2018

module typedat
implicit none
    type :: dat
        integer :: trow,tcol,tnum,nin,nout
        type(dat),pointer,dimension(:)::next    !Pointer to an array of things of type dat,so find a way to store prev or next into array
        type(dat),pointer,dimension(:)::prev !Pointer to an array of things of type dat

end type

end module

program multipleio
use typedat
implicit none
    integer,allocatable,dimension(:)::torder2,torder1,torder3,allt
    type(dat),target,dimension(:),allocatable::totdat
    type(dat),pointer::head,temp,temp1
    type(dat),pointer::first(:),last(:),prevdup(:),nextdup(:),prev1dup(:),next1dup(:)
    integer,dimension(:),allocatable :: a(:),b(:)

    open(17,file='tuborder.txt')
        do i=1,ttub
            allocate(a(totdat(i)%nin),b(totdat(i)%nout))
            read(17,*) a(1:totdat(i)%nin),b(1:totdat(i)%nout)
            allocate(prevdup(totdat(i)%nin,nextdup(totdat(i)%nout))
            if (totdat(i)%nin .gt. 0) then
                do j=1,totdat(i)%nin
                    do k=1,ttub
                        if (a(j)==totdat(k)%tnum) then
                            temp=>totdat(k)
                            prevdup(j)=temp
                        end if
                    end do
                end do
            end if
            totdat(i)%prev=>prevdup(1:totdat(i)%nin) !Linking the current tube as previous tube for next tube
            if (totdat(i)%nout .gt. 0) then
                do j=1,totdat(i)%nout
                    do k=1,ttub
                        if (b(j)==totdat(k)%tnum) then
                            temp=>totdat(k)
                            nextdup(j)=temp
                        end if
                    end do
                end do
            end if
            totdat(i)%next=>nextdup(1:totdat(i)%nout)!Linking the next tube to current tube
            deallocate(a,b)
        end do
    close(17)

I am trying to write a program to follow flow inside tubes. I planned to use linked list with pointer "next" in my data structure shall point to the next tube of the path.I am facing a problem to link the various tubes when i am having multiple inlets or outlets for a tube. I want my current tube to point to next tube via next pointer and similarly to its previous tubes via prev pointer. If multiple inlets and outlets are there i am reading them into an arrays a,b and using them. Derived structure of "type (dat)" above contains tube information. The underlined lines above are the major concern for me. When i am using => in those lines i am getting an error of this kind

Error 1 error #8524: The syntax of this data pointer assignment is incorrect: either 'bound spec' or 'bound remapping' is expected in this context

and when i am just using = as above my pointers links are not coming correctly. I am new to Fortran and got stuck, kindly help me with this.

mecej4 · ‎03-20-2018

The flaw in your design is that you intend nextdup and prevdup to be arrays of pointers as in C and other languages. This is not allowed in Fortran. You can, on the other hand, embed a pointer inside a new type, say dupptr_type, and declare an array of this type.

Reddy__Karunakar · ‎03-20-2018

            if (totdat(i)%nin .gt. 0) then
                do j=1,totdat(i)%nin
                    do k=1,ttub
                        if (a(j)==totdat(k)%tnum) then
                            pdup(j)%prevdup=>totdat(k)          ! pdup is a type having pointer prevdup
                        end if
                    end do
                end do
            end if
            totdat(i)%prev=>pdup(1:totdat(i)%nin)%prevdup !Linking the current tube as previous tube for next tube
            if (totdat(i)%nout .gt. 0) then
                do j=1,totdat(i)%nout
                    do k=1,ttub
                        if (b(j)==totdat(k)%tnum) then
                            ndup(j)%nextdup=>totdat(k)         ! ndup is a type having pointer nextdup
                        end if
                    end do
                end do
            end if
            totdat(i)%next=>ndup(1:totdat(i)%nout)%nextdup     !Linking the next tube to current tube
            deallocate(a,b,pdup,ndup)
        end do

I did the changes, but how to append this to next and prev pointers of type dat. I know that the above highlighted way is not correct as again it will take that statement as array of pointers which is not possible in fortran. How do i change the above code so that i can point next to an array of next tubes and prev to an array of prev tubes?

FortranFan · ‎03-21-2018

@Reddy, Karunakar,

You may want to go through the thread link below in detail, in particular the technique recommended in Quote #13 - you may find it helpful.

https://software.intel.com/en-us/forums/intel-visual-fortran-compiler-for-windows/topic/755612