Here’s a little toy example: subroutine print_present(opt, name) implicit none real, intent(in), dimension(:), optional :: opt character(len=*), intent(in) :: name print*,name, present(opt) end subroutine print_present Passing a zero-sized array seems to result in what looks li…

Looks like a gfortran bug. According to the F2018 standard interpretation document (J3/18-007r1), section 15.5.2.12 it should be “present”, no matter whether zero or non-zero sized. Interestingly (regarding your snippet on goldbolt.org ), the presence of an unallocated array being passed as an optio…

Well that is a bit of a pain with the unallocated variables, because it also means type information is not passed along, or you need another overload to make the dummy argument allocatable. I’m not sure that that is a good feature. Looks like the zero-sized literal is definitely a bug though, thank…

Bug or undefined behaviour in passing zero-sized arrays as optional argument?

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Beliavsky November 16, 2021, 11:55am 3

Please see the thread An unallocated variable passed as an argument is not PRESENT .

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Bug or undefined behaviour in passing zero-sized arrays as optional argument?

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