Fortran 90存在可选参数 [英] Fortran 90 Presence Of Optional Arguments

问题描述

我不明白使用pgf90 7.2的present（）内在函数的行为。我写了一个20行的示例程序来测试这个，但结果对我来说仍然没有意义。注意：

I do not understand the behavior of the present() intrinsic function with pgf90 7.2. I wrote a 20 line sample program to test this, but the results still make no sense to me. Observe:

subroutine testopt(one,two,three,four,five)

  implicit none

  integer, intent(in) :: one,two
  integer, intent(out) :: three
  integer, intent(in), optional :: four
  integer, intent(out), optional :: five

  three = one + two

  print *,"present check: ",present(four),present(five)

  if (present(four) .and. present(five)) then

  five = four*four

end if

end subroutine testopt

如果我：call testopt（1,2， （任何变量））从我的主程序，它打印：现在检查：TF。但是，如果我从子程序中调用testopt（1,2，（任何变量）），它将打印：当前检查：T T。我希望在任何一种情况下都能看到现在的检查：F F，因为我只用3个非可选参数调用子程序，而没有任何可选参数。我无法理解为什么它会以这种方式行事，这导致了我正在开发的程序中的一个重大错误。我感谢任何见解。感谢。

if I: call testopt(1,2,(any variable)) from my main program, it prints: "present check: T F". However if I: call testopt(1,2,(any variable)) from a subprogram it prints: "present check: T T". I expected to see "present check: F F" in either case, because I am only calling the subroutine with the 3 non-optional arguments, and neither of the optional ones. I cannot fathom why it would behave this way, and this is causing a major bug in a program I am working on. I appreciate any insight. Thanks.

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