>>> Anytime a new scalar (i.e. non-array) variable is created, the addresses of >>> the array variables must all change to make room for the new scalar >>> variable.
So BASIC copies all the arrays to a new memory address? That does not seem very efficient. Jeff From: M100 <m100-boun...@lists.bitchin100.com> On Behalf Of Ken Pettit Sent: Monday, May 28, 2018 10:24 PM To: m...@bitchin100.com Subject: Re: [M100] interesting VARPTR bug Steve, John is correct. Array variables are stored at a higher memory address than scalar variables. Anytime a new scalar (i.e. non-array) variable is created, the addresses of the array variables must all change to make room for the new scalar variable. So the return value from VARPTR for array variables is only valid for as long a there are no new scalar variables delcared. Ken On 5/28/18 4:37 PM, Stephen Adolph wrote: sounds plausible. for reference here is the code. I have 4 embedded ML programs that I want to select to run. 2 REM good command sequence 3 A$(0)="using good sequence":D$(0)="ó:@ð:@ð:¸ð:òð:4ð:°ð:1ð:¿ð77~2ÀüûÉ" 4 REM bad command sequence add 7 after 4@ 5 A$(1)="using bad sequence1":D$(1)="ó:@ð:@ð:¸ð:òð:4ð7:°ð:1ð:¿ð77~2ÀüûÉ" 6 REM bad command sequence 2 add 7 after 77 7 A$(2)="using bad sequence2":D$(2)="ó:@ð:@ð:¸ð:òð:4ð:°ð:1ð:¿ð77&~2ÀüûÉ" 8 REM bad command sequence 3 remove 7 from 77 9 A$(3)="using bad sequence3":D$(3)="ó:@ð:@ð:¸ð:òð:4ð:°ð:1ð:¿ð7~2ÀüûÉ" 10 CLS:PRINT"Send command + data to REXCPM" 11 INPUT"select command sequence (1-4)";S:IF S<1 OR S>4 THEN 10 12 S=S-1 20 PRINT A$(S):F=0:K=VARPTR(D$(S)):F=256*PEEK(K+2)+PEEK(K+1) 21 PRINTF 22 FORI=1TOLEN(D$(S)):IF ASC(MID$(D$(S),I,1)) <> PEEK(F+I-1) THEN BEEP:PRINT"bad!":END 23 NEXTI:PRINT"good!!" 30 INPUT"Enter command byte";L 40 INPUT"enter data byte";H 50 CALLF,0,256*H+L 60 PRINT"result = ";PEEK(64704) 70 PRINT"hit any key to repeat" 80 IFINKEY$=""THEN 80 90 GOTO10 On Mon, May 28, 2018 at 7:36 PM, John R. Hogerhuis <jho...@pobox.com <mailto:jho...@pobox.com> > wrote: On Mon, May 28, 2018 at 4:29 PM Stephen Adolph <twospru...@gmail.com <mailto:twospru...@gmail.com> > wrote: yes, I do have a dim but ..not sure it matters though. I think I tried with and without. Hmm. Not sure how the basic variable allocator works. But if putting F=0 makes it work or not work I suspect that assigning F for the first time creates a new variable and caused the array to move. DIM’ing either or both, or assigning a value like you did might resolve. Whether that’s a bug I don’t know. Maybe you just need to be careful not to allocate variables between when you take VARPTR and when you use it the address. — John
