What is the point of BLOCK in Fortran?

Question

I am looking at some code and there is this:

BLOCK

...lines of code...

END BLOCK

What is the purpose of BLOCK? I tried to go

Answer 1

From the Fortran 2008 standard:

The BLOCK construct is an executable construct that may contain declarations.

It is not related to common blocks or to block data program units.

So, the main use is this "containing declarations".

As scoping units we have things like

integer i
block
  integer j ! A local integer
  integer i ! Another i
  save i    ! ... which can even be SAVEd
end block

which affords locality of declarations:

! ... lots of code
block
  integer something
  read *, something
end block
! ... lots more code

These scoping blocks allow automatic objects:

integer i
i = 5
block
  real x(i)
end block

As executable constructs, they also have useful flow control:

this_block: block
  if (something) exit this_block
  ! ... lots of code
end block

They also have finalization control:

type(t) x
block
  type(t) y
end block ! y is finalized
end  ! x is not finalized

for x and y of finalizable type.

Oh, and let's not forget how you can confuse people with implicit typing.