From: glynnec AT ix DOT netcom DOT com (Glynne Casteel)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: f2c+djgpp
Date: 12 Jan 1997 18:44:42 GMT
Organization: Netcom
Lines: 50
Message-ID: <5bbbeq$h8@dfw-ixnews12.ix.netcom.com>
References: <9701121422 DOT AA18628 AT cambridge DOT scr DOT slb DOT com>
NNTP-Posting-Host: den-co14-24.ix.netcom.com
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

In <9701121422 DOT AA18628 AT cambridge DOT scr DOT slb DOT com> combee AT cambridge DOT scr DOT slb DOT com
(Leendert Combee) writes: 
>
>  Fortran example:
>
>  subroutine test(a,n)
>  integer n,i
>  real    a(n)
>  do i = 1, n
>     a(i) = ....
>  end do
>  return
>  end
>
>  This gets translated into a few lines of c-code, the crucial bit being:
>  
>    /* Parameter adjustments */
>    --a;
>
>  (the reason being that a[1] is now really the first element (index 0) of the
>  original array). THE PROBLEM IS THAT POINTER a IS **NEVER** RESET: ++a
>  So that if test is called twice, the pointer a is decreased *again*. 
>  I could not believe this when inspecting code, but I got suspicious when
>  f2c+djgpp compiled code gave different results than f77 on unix.
>
>  Anyone any comments?? Anyone with a more recent f2c willing to check
his/her
>  code or the above simple example?

This is no cause for concern; a does not need to be reset!  The reason
is that it is passed in as a pointer to the function.  Something like
[I assume]: 

   void test( double *a, int n )
   {
    /* decrementing a here has no effect on its value 
     * in the calling program!!
     */
    a--;  /* calling program cannot see this */

    /* HOWEVER changing the values that it points to 
     * will be reflected in the calling program
     */
    a[1] = 16.0;   /* calling program CAN see this change */

   }