CODEWITHSUNDEEP
loopsmodulefortranexitsubroutine
user6501555
user6501555

Reputation:

Exit outer loop from subroutine without logical variable

Following minimal example:

L1: do while(.true.)
    L2: do while(.true.)
        if(something=.true.) exit L1
    end do L2
end do L1

So now i want to write the inner Loop L2 into a subroutine within a seperate module to link them together when compiling the code, like gfortran main.f95 innerloop.o -o somename

module innerloop
contains 
    subroutine innerloop()
    L2: do.....
        if(something=.true.) exit L1
    ...
end module innerloop

I get various errors, even when i set the loops name to a global character via a module with global variabels. Because of a huge number of various if cases it is no idea to define a globle variable as a flag and do something like: if(something=.true.) exitvar=.true. and then to write an if-case behind every subroutine or function if the variable is .true. or not and exit all the loops step by step. Is there another way to exit an outer loop from an inner one within a seperate subroutine in de module?

Upvotes: 1

Views: 702

Answers (1)

High Performance Mark
High Performance Mark

Reputation: 78364

Your approach breaches Fortran's rules concerning the scope of 'jumps', whether they be exits or gotos or similar constructs. In other words you can forget about exit-ing from a labelled do-loop in the way you propose.

I get various errors, even when i set the loops name to a global character Yes, the construct-name on a do (or similar) construct is not a character variable or constant or any other thing that can be set during execution.

This, Fortran's sanity on the scoping of jumps, is a good thing which makes it harder to write spaghetti code. You don't want to use a global variable as a flag, nor should you want to. Use a local variable, perhaps something like this

module innerloop
contains 
    subroutine innerloop(l1return)
    logical, intent(out) :: l1return
    l1return = .false.
    L2: do.....
        if (something) then
          l1return = .true.
          exit L2
        end if
    ...
end module innerloop

Yes, you now have to test whether the subroutine finished early or not, but that is a small price to pay to avoid the madness that follows from unconstrained jumping from scope to scope.

Upvotes: 4

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