direct indexing on function return value in fortran

问题

Is there posibility to use indexing directly on a function's return value? Something like this:

readStr()(2:5)

where readStr() is a function which returns a character string. In many other languages it is quite possible, but what about Fortran? The syntax in my example of course does not compile. Is there any other syntax to be used?

回答1:

No, that is not possible in Fortran. You could, however, alter your function to take an additional index array that determines which elements are returned. This example illustrates this possibility using an interface to allow for an optional specification of the indices (simplified greatly thanks to the comment by IanH):

module test_mod
  implicit none

  contains

  function squareOpt( arr, idx ) result(res)
    real, intent(in)              :: arr(:)
    integer, intent(in), optional :: idx(:)
    real,allocatable              :: res( : )
    real                          :: res_( size(arr) )
    integer                       :: stat

    ! Calculate as before
    res_ = arr*arr

    if ( present(idx) ) then
      ! Take the sub-set    
      allocate( res(size(idx)), stat=stat )
      if ( stat /= 0 ) stop 'Cannot allocate memory!'

      res = res_(idx)
    else
      ! Take the the whole array    
      allocate( res(size(arr)), stat=stat )
      if ( stat /= 0 ) stop 'Cannot allocate memory!'

      res = res_
    endif

  end function
end module

program test
  use test_mod
  implicit none

  real    :: arr(4)
  integer :: idx(2)

  arr = [ 1., 2., 3., 4. ]
  idx = [ 2, 3]

  print *, 'w/o indices',squareOpt(arr)
  print *, 'w/  indices',squareOpt(arr, idx)
end program

回答2:

No.

But if it bothers you, you can write your own user defined functions and operators to achieve a similar outcome without having to store the result of the function reference in a separate variable.

来源：https://stackoverflow.com/questions/28762841/direct-indexing-on-function-return-value-in-fortran