Error after allocating array components in a derived type array

Question

module sdata

    integer, parameter :: nblock = 2

    TYPE block_info

        REAL, ALLOCATABLE :: w(:)

    END TYPE block_info

    TYPE(block_info), TARGET :: block(nblock)

end module sdata





module variable

    use sdata

    REAL, POINTER :: w(:)

contains

    !.............................
    subroutine set_current(n)

    nullify(w)
    allocate(w(10))

    w(1:10)  => block(n)%w(1:10)

    end subroutine set_current
    !.............................

end module variable


subroutine make_sth

use variable
use sdata

real,allocatable,dimension(:)::wm,wp,ww
integer n

allocate(wm(5),wp(5),ww(5))


do n = 1,nblock

    block(n)%w(1:10) = (/ 1.,2.,3.,4.,5.,6.,7.,8.,9.,10./)

    call set_current(n)

    wp(1:5) = w(1:5)
    wm(1:5) = w(6:10)

    ww = wp + wm

    do i = 1,5
        print*, 'block = ',n,'ww = ',ww(i)
    enddo

enddo

end subroutine make_sth


program main

use variable
use sdata

allocate(block(nblock)%w(10))

call make_sth

end program main

Here is my question. For nblock=1 code is perfectly running, however, if I increase nblock ie. to 2 it gives memory problems. How is it possible?

Please look at reducing the spacing of your code as all those blank lines make it hard to follow. — francescalus
– francescalus, Commented Feb 3, 2017 at 9:27
Please do not use uncertain phrases like "it gives memory problems". If it prints some error message, paste it into your question. Read How to Ask — Vladimir F Героям слава
– Vladimir F Героям слава, Commented Feb 3, 2017 at 9:50

francescalus · Accepted Answer · 2017-02-03 09:35:57Z

2

Let's look at the allocation of the array components of the derived type. In particular the line in the main program

allocate(block(nblock)%w(10))

This is not doing what you think it is, it seems.

What happens here is that the component w of the element nblock of block is allocated. It isn't saying that the nblock components of block are all allocated to that size. When nblock is 1, the effect is the same: no problem.

You need to allocate each element's component individually. Which makes sense, as one would often like each element to have differently sized components, or varying allocation status. There are several approaches for this, but I won't cover those here: there are other questions for that.

answered Feb 3, 2017 at 9:35

francescalus

32.9k28 gold badges86 silver badges128 bronze badges

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

1 Comment

atelcikti1 Over a year ago

This is just like ABC of fortan90, thank you for remembering it. Sorry for this silly question.

Pierre de Buyl · Accepted Answer · 2017-02-03 09:36:43Z

1

Change

allocate(block(nblock)%w(10))

to

do i = 1, nblock
    allocate(block(i)%w(10))
end do

In you current code, you only allocate one element of block: either block(1)%w(10) if nblock=1 or block(2)%w(10) if nblock=2. With the modification I propose you will allocate an array w inside of each element of block.

answered Feb 3, 2017 at 9:36

Pierre de Buyl

7,3232 gold badges18 silver badges23 bronze badges

Collectives™ on Stack Overflow

Error after allocating array components in a derived type array

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related