Fortran increase dynamic array size in function

Question

I need a variable size array in Fortran. In C++ I would use vector. So I have a function like

integer function append(n, array, value)
  integer, pointer, d         


        

Answer 1

OK, the problem is that you cannot deallocate and re-allocate the array that you are assigning a function value to. You are correct about the cause of your problem (arguments passed by reference and not by value as it is in C). Since you deallocate the array inside the function body, the assignment to that array becomes invalid, leading to segfault. This is not a gfortran issue, tried it with ifort and pgf90, all of them report the same problem. This works for me:

PROGRAM dynamic_size
INTEGER,DIMENSION(:),ALLOCATABLE :: array

ALLOCATE(array(10))

array=(/1,2,5,7,4,3,6,5,6,7/)

WRITE(*,*)SIZE(array)
CALL resize_array
WRITE(*,*)size(array)

CONTAINS

SUBROUTINE resize_array
INTEGER,DIMENSION(:),ALLOCATABLE :: tmp_arr

ALLOCATE(tmp_arr(2*SIZE(array)))
tmp_arr(1:SIZE(array))=array
DEALLOCATE(array)
ALLOCATE(array(size(tmp_arr)))
array=tmp_arr

ENDSUBROUTINE resize_array

ENDPROGRAM dynamic_size