Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!sun-barr!newstop!sun!rushforth!kcr
From: kcr%rushforth@Sun.COM (Kevin Rushforth)
Newsgroups: comp.sources.games.bugs
Subject: Re: Ularn bug -- selling the same gem more than once
Message-ID: <115011@sun.Eng.Sun.COM>
Date: 12 Jul 89 04:04:58 GMT
References: <114443@sun.Eng.Sun.COM> <34458@bu-cs.BU.EDU>
Sender: news@sun.Eng.Sun.COM
Reply-To: kcr@sun.UUCP (Kevin Rushforth)
Organization: Sun Microsystems, Mountain View
Lines: 53

In article <34458@bu-cs.BU.EDU> adb@bu-cs.bu.edu (Adam Bryant) writes:
>In article <114443@sun.Eng.Sun.COM> kcr%rushforth@Sun.COM (Kevin Rushforth) writes:
>>There is a bug in larn that was carried over into Ularn which allows
>>one to sell a gem an unlimited number of times.  To reproduce this
>
>You really don't need to create the extra loop to fix that bug.
>The array gemvalue is declared as a static array and therefore saves
>its value between calls to the function.
>
>Simply remove the word 'static' from the declaration of gemvalue
>and the problem will be solved.

Not quite.  Here is the relevant piece of store.c

------------------------------
static short gemorder[26]={0};	/* the reference to screen location for each */
static long gemvalue[26]={0};	/* the appraisal of the gems */

obanksub()
{
	long amt;
	register int i,k;
	ointerest();	/* credit any needed interest */

	if (level==8) c[TELEFLAG] = 0;

/****** HERE IS THE LOOP TO INITIALIZE THE ARRAY ******/
	for(i = 0; i < 26; i++)
		gemvalue[i] = 0;
/****** END OF THE LOOP TO INITIALIZE THE ARRAY ******/

	for (k=i=0; i<26; i++)
		switch(iven[i]) {

[...more stuff...]

Since the array is declared outside the obanksub() routine, removing
the word static would not change the fact that the array keeps its
value between calls to the function.  All that it would do is make the
global array gemvalue[] externally visible (not a good idea unless you
have a reason).  Even if you were to move the array declaration into
the obanksub() function and then remove the 'static' keyword, you would
still have to initialize it.  Automatic variables in "C" (including
arrays) are not initialized upon entry into a function.  The patch that
I posted is the easiest way around the bug without modifying the logic
of the routine.

-- 
Kevin C. Rushforth                   | "If winning is not important,
Sun Microsystems                     |  then commander, why keep score?"
                                     |              - Lt. Worf
ARPA: kcr@sun.com                    |
UUCP: <most-backbone-sites>!sun!kcr  |