Array of pointers

[Screeb]

Hi, I'm trying to create an array of pointers. Well, the objective is an array of objects, which can contain any object that extends a certain base class.

I have a base class "object", and a derived class "sphere" ("TYPE, extends(object) :: sphere"). Here's an example of what I'm trying to do:

class(object), pointer :: objects(:)
type(sphere), target :: s1

ALLOCATE(objects(0:numObjects-1), mold=s1)
objects(0) => s1

The last line gives error #8524 "The syntax of this data pointer assignment is incorrect: either 'bound spec' or 'bound remapping' is expected in this context. [0]"

However, the following works fine (but I need an array):

class(object), pointer :: obj
type(sphere), target :: s1
obj => s1

One thing that sort of works is "objects(0:0) => s1", but that seems to resize the array to 0:0.

What am I doing wrong?

[Steven_L_Intel1 · Accepted solution]

The concept of "array of pointers" does not exist in Fortran. The way you have to do it is have an array of derived type with a pointer component. So something like this:

[fortran]type container
  class(object), pointer :: obj
end type container

type(container), allocatable, dimension(:) :: objects
allocate (objects(0:num_objects))
objects(0)%obj => s1[/fortran]

[Screeb]

Ah, thanks, that works. A bit messier than I would have liked, but oh well.

[jimdempseyatthecove]

Screeb,

You can cleanup the messiness by using an FPP macro.
However, the VS Debugger will not expand the macro (a feature I would like to see added), thus debugging is a bit complicated as you have to manually expand the macro in your watch expressions.

I use this technique a lot since it makes reading the code much clearer.

You can use an inlined function in Fortran on the RHS of =but unfortunately you cannot use it on the LHS of =. You can use an FPPmacro on either side.

Jim Dempsey