restrict dimensions for allocatable arrays

[EvgeniyZh]

Hello,
I'm just writing some code in Fortran 90 and compiling it with ifort. For some data I need arrays of size e.g. 3 x n, where n is determinded at runtime. AFAIK fortran does not allow to restrict any dimension of my allocatable array, so in fact the arrays intended to be 3 x n could be allocated as m x n, where m could be random. I thought of defining a datatype for a 3-dimensional vector, but that would slow down the intrinsic vecotr operations and I would have to rewrite some standart operations by hand (e.g. + or *). Additionally some overhead would be produced because I would use a custom type. Is there any possibility to restrict one of the dimensions for an allocatable array, without running into trouble described above? (I would need something like
real, allocatable :: A(3,).

 

[xwb]

If you mean restrict it in the declaration, no. Best bet is to check before allocation.

 

[EvgeniyZh]

Thanks a lot! Yes, I meant in the declaration. It's a pity...

 

[xwb]

You could always do something like

subroutine malloc(A, nsize)
real, allocatable, intent(inout)::A(3,:)
integer, intent(in):: nsize
integer, parameter:: maxallowed = 1000

if (nsize .gt. maxallowed) then
   print *, 'Array size ', nsize, ' exceeds max ', maxallowed
   stop
end if
allocate (A(3:nsize))
return
end

Then call malloc instedad of allocate.