# How to expand the scope of a subroutine inside a subroutine? **URL:** \ **Category:** Uncategorized\ **Created:** [July 20, 2022, 5:55am UTC](https://fortran-lang.discourse.group/t/how-to-expand-the-scope-of-a-subroutine-inside-a-subroutine/4031 "2022-07-20T05:55:39Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![CRquantum](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/crquantum/32/730_2.png) [@CRquantum](https://fortran-lang.discourse.group/u/CRquantum)\ **Post date:** [July 20, 2022, 5:55am UTC](https://fortran-lang.discourse.group/t/how-to-expand-the-scope-of-a-subroutine-inside-a-subroutine/4031/1 "2022-07-20T05:55:39Z")
Dear all, A quick question, for an extremely simplified example, ```auto subroutine A(n) integer :: n if (n>100) then write (6,*) 'Rich!', n return else write (6,*) 'Poor!', n return endif write (6,*) 'This is line shall not be displayed.' end subroutine A ``` Now, for some reason I want the above subroutine `A` to be written as subroutine `A_mod`. `A_mod` and `A` should behave exactly the same. That is, the text "This is line will not be displayed.‘’ really should not be displayed in both `A_mod` and `A` . I define sub subroutine `show` inside `A_mod` to simplify the write and return statements. In real case these write and return statements are actually some long and similar code. That is why I want to use sub subroutine `show`, so that I do not need to repeat some similar code blocks explicitly again and again. So I make Amod as below, ```auto subroutine A_mod(n) integer :: n if (n>100) then call show('Rich!',*100) else call show('Poor',*100) endif write (6,*) 'This is line shall not be displayed.' 100 return ! sub subroutine show should just to here. contains subroutine show(ch,*) character(*) :: ch write (6,*) ch, n return 1 end subroutine show end subroutine A_mod ``` So that the sub subroutine `show` is really return to the proper place in the subroutine A\_mod, which is ```auto 100 return ``` Here I used alternative return, [https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vnb3/index.html](https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vnb3/index.html) I know it looks like using alternative return, I can let sub subroutine `show` to jump to any place in subroutine `A_mod` as I want to. However it seems alternative return may be an obsolete feature (however it seems very useful in this case). So anyway, I just wonder, is there any other modern way to let sub subroutine (such as `show`) jump to certain places in the main subroutine (such as `A_mod`)? Thanks much in advance! ---
**Author:** ![ivanpribec](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/ivanpribec/32/3290_2.png) [@ivanpribec](https://fortran-lang.discourse.group/u/ivanpribec)\ **Post date:** [July 20, 2022, 7:15am UTC](https://fortran-lang.discourse.group/t/how-to-expand-the-scope-of-a-subroutine-inside-a-subroutine/4031/2 "2022-07-20T07:15:01Z")
Apart from `go to` and alternative returns which lead to complicated control flow, you could do this: ```fortran logical :: skip skip = .true. write(*,'(A)',advance='no') "n = " read(*,*) n if (n > 100) then write(*,*) "Rich" else write(*,*) "Poor" end if ! ... [insert code to change skip to .false.] ... if (.not. skip) then write(*,*) "This line shall not be displayed" end if end ``` As it stands now, the example makes little sense, because the last write is bound to be skipped under all normal circumstances. I am guessing in your true code there might be additional statements between the two else blocks. ---
**Author:** ![CRquantum](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/crquantum/32/730_2.png) [@CRquantum](https://fortran-lang.discourse.group/u/CRquantum)\ **Post date:** [July 20, 2022, 8:49am UTC](https://fortran-lang.discourse.group/t/how-to-expand-the-scope-of-a-subroutine-inside-a-subroutine/4031/3 "2022-07-20T08:49:36Z")
Thank you @ivanpribec . Yeah the example I showed is not too good. The real code contains a little bit MPI, and it is more like ```auto subroutine A(...) ... do i = 1, n if ( rank ==0 ) then ! rank 0 cpu do the job. ! However at some point if rank 0 find error, ! it wants to inform all the cores to return ... long god damn code ... if (detected some error) then quit= .true. goto 100 else quit = .false. endif ... long god damn code ... endif 100 continue call broadcast(quit) if (quit) then return ! all core will wait here for rank 0 to broadcast if quit or not. ! if quit is true then all the cores return. enddo ... end subroutine A ``` 1. It looks like in this case, if rank 0 detects some error, and it wants all the cores to return, I can think of the not-so-adorable `goto` statement is convenient. All the cores will run at `100`, and wait for the `broadcast`, when `quit` is true, all the cores return subroutine `A`. Is there some other way can achieve this? I mean, if rank 0 detects something wrong, if inform all the cores to stop or return or whatever. 2. if I want to make ```auto ... long god damn code ... if (detected some error) then quit= .true. goto 100 else quit = .false. endif ... long god damn code ... ``` into a sub subroutine inside subroutine `A`, call it `longcode`, like ```auto subroutine A(...) ... do i = 1, n if ( rank ==0 ) then ! rank 0 cpu do the job. ! However at some point if rank 0 find error, ! it wants to inform all the cores to return call longcode(...) endif 100 continue call broadcast(quit) if (quit) then return ! all core will wait here for rank 0 to broadcast if quit or not. ! if quit is true then all the cores return. enddo ... contains subroutine longcode(...) ! seems need to use alternative return, ! so that it return to 100 in the main subroutine. end subroutine longcode end subroutine A ``` It seems the alternative `return` will be needed in sub subroutine `longcode`. Is there some more modern way that can let sub subroutine `longcode` jump to some places in the main subroutine `A`? Sorry it is a little bit chaotic, lol. ---
**Author:** ![FedericoPerini](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/federicoperini/32/1750_2.png) [@FedericoPerini](https://fortran-lang.discourse.group/u/FedericoPerini)\ **Post date:** [July 20, 2022, 9:29am UTC](https://fortran-lang.discourse.group/t/how-to-expand-the-scope-of-a-subroutine-inside-a-subroutine/4031/4 "2022-07-20T09:29:51Z")
The usual way to do this is to use error/return flags from your routine: ```fortran ! Only rank 0 will run this function integer(STATUS_CODE) function do_your_job(bla,bla) result(ierr) ierr = STATUS_SUCCESS ! default: all good ! On errors of any kind, return an error code if (problem) then ierr = STATUS_PROBLEM_1 return endif end function do_your_job ``` Of course you need to define your error codes somewhere as `PARAMETER`s . The usual logic simplifies math in MPI and is usually: - ierr == 0 : success, no more info - ierr\>0: success, return some info - ierr\<0: error code so you can later do ```auto if (rank==0) then ierr = do_your_job(blabla) else ierr = SUCCESS endif ! Gather error code ierr = MPI_ALLREDUCE(ierr,MPI_MIN,blabla) if (ierr<0) stop ' error occurred ' ``` ---
**Author:** ![FedericoPerini](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/federicoperini/32/1750_2.png) [@FedericoPerini](https://fortran-lang.discourse.group/u/FedericoPerini)\ **Post date:** [July 20, 2022, 9:35am UTC](https://fortran-lang.discourse.group/t/how-to-expand-the-scope-of-a-subroutine-inside-a-subroutine/4031/5 "2022-07-20T09:35:06Z")
You want to give your error codes an `ENUM`-like status: ```fortran integer, parameter :: STATUS_CODE = int32 ! define a kind integer(STATUS_CODE), parameter :: STATUS_SUCCESS = 0 integer(STATUS_CODE), parameter :: STATUS_INVALID_INPUT = -1 integer(STATUS_CODE), parameter :: STATUS_INVALID_OUTPUT = -2 ! etc. ``` ---
**Author:** ![simong](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@simong](https://fortran-lang.discourse.group/u/simong)\ **Post date:** [July 20, 2022, 9:45pm UTC](https://fortran-lang.discourse.group/t/how-to-expand-the-scope-of-a-subroutine-inside-a-subroutine/4031/6 "2022-07-20T21:45:19Z")
Can’t you just use a label on the if statement and exit to it: ```auto rank0: if ( rank ==0 ) then ! rank 0 cpu do the job. ! However at some point if rank 0 find error, ! it wants to inform all the cores to return ... long god damn code ... if (detected some error) then quit= .true. exit rank0 else quit = .false. endif ... long god damn code ... endif rank0 ``` Personally I like alternate returns and am hoping that one day they’ll make a comeback. The status code example below shows the unnecessarily verbosity which is one of Fortran’s weaknesses. Perhaps one day we’ll get the equivalent of enum class (C++) Your code also shows a limitation of internal procedures - you can’t invoke a return from the calling code. In scripting languages (well tcl at least) you can invoke a return by just specifying the level, e.g. `return -level 1 -code ok` Extending `return` to the functionality of tcl would give internal procedures a serious boost.