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fortranoptional-arguments

Is it necessary to check an optional argument before passing it to another optional argument?

I have the following question concerning the usage of optional argument. Let's say I have the following routine aaa defined in module m_aaa

MODULE m_aaa
SUBROUTINE aaa(a, b)
  INTEGER           :: a
  INTEGER, OPTIONAL :: b
END SUBROUTINE
END MODULE

now I have a second routine that uses the module m_aaa. Is it possible to pass the optional argument like this

! Variant 1:
SUBROUTINE bbb(c, d)
  USE m_aaa 
  INTEGER           :: c
  INTEGER, OPTIONAL :: d
  CALL aaa(c,d)
END SUBROUTINE

or is it necessary to check the presence of the optional argument d like this:

! Variant 2:
SUBROUTINE bbb(c, d)
  USE m_aaa 
  INTEGER           :: c
  INTEGER, OPTIONAL :: d
  IF (PRESENT(d)) THEN
    CALL aaa(c,d)
  ELSE
    CALL aaa(c)
  ENDIF
END SUBROUTINE

Thanks for your help.

Solution

  • It is not necessary to check to presence of an optional dummy argument before passing it as an actual argument to another optional dummy argument.

    This is allowed by 12.5.2.12 paragraph 4 (ISO/IEC 1539-1 (Draft 7 June 2010) aka Fortran 2008) regarding optional actual arguments that are not present:

    Except as noted in the list above, it may be supplied as an actual argument corresponding to an optional dummy argument, which is then also considered not to be present.