(j3.2006) Restrictions on side-effects for (non pure) functions?

[Tom Clune]

I client sent an example that appears to produce incorrect answers under gfortran, but the expected results on other compilers.  (Intel, NAG).   A function with a side effect is used to return an index for an array reference.   This works if the function is evaluated once, but it appears to be evaluated twice with gfortran.

Before we file a bug report, I?m concerned that the abuse of side-effects is violating some prohibition in the standard.   I?ve found several vague but ominous warnings on various websites, but have not found any relevant language in the latest standard.

Aside from the dubious programming practice - is the following a standard conforming code?


MODULE belt_and_suspenders
CONTAINS

  INTEGER FUNCTION next(cnt)
    INTEGER, INTENT(INOUT) :: cnt
    cnt = cnt + 1
    next = cnt
  END FUNCTION next

END MODULE belt_and_suspenders

PROGRAM tryit
   USE belt_and_suspenders
   IMPLICIT NONE

   CHARACTER(LEN=64), DIMENSION(2) :: c
   INTEGER :: cntc
  
   cntc = 0
   c(next(cntc)) = 'a'

  WRITE(6,*) cntc

END PROGRAM tryit






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