Allocatable array defined or not

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1 
program test
  use ieee_arithmetic, only: ieee_value, ieee_quiet_nan
  real(8) :: x1(5)
  real(8), allocatable :: x2(:)
  allocate(x2(5))
  x1(1) = ieee_value(0d0, ieee_quiet_nan)
  x2(1) = ieee_value(0d0, ieee_quiet_nan)
  print *, x1(2:5)
  print *, x2(2:5)
end program

In the program above, x1(2:5) is undefined, is x2(2:5) undefined or defined as zeros?

2

I don’t see any fundamental difference from your previous question: Undefined variables

4

It is a different question. I am uncertain whether assigning value to one element of an allocatable array will make the other elements defined as zeros.

5

Just use sourced allocation to initialize arrays to zero and don’t worry about it.

allocate(x2(5), SOURCE=0.0d0)
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