May June 1980 - Commodore Computers

MAY/JUNE. I 1980 I960. . ISSUE 4. 4 COMPUTE. 9Q
Atari Tape Data Files
Atari Tape Data Files
A Consumer Oriented Approach
Introduction
This article is based on a major axiom of consumer
computing:
Easier is Better
The specific coroll ary when writing a program which
The specific corollary when writing a program which
saves data between program runs is:
Use only one tape. Program and data should be on the
same tape. They should, in fact, be the same thing.
A consumer should be able to load his program, run
it 10 to update hiss checkbook and balance hiss budget, and
then save the program on tape when done. The next
day, he can load his program and all data changes
from the previous day should be there.
" Impossible", you say? Well , perhaps. It is cer­
"Impossible", you say? Well, perhaps. It is cer
tainly y impossible on some of the computers on the
market. But it is not impossible on the Alari. Atari. The trick
is to fool Atari Basic into saving all dimensioned
variables when a program is saved to tape. We won't
try 10 save the simple variables. Since I am not a
try to save the simple variables. Since I am not a
revered expert, I won't make the mistake of saying
this is impossible. (But, I think it's impossible.)
this is impossible. (But, I think it's impossible.)
Saving the dimensioned variables with a program is
relatively easy.
Write your program
Listing 1 is a simple program. Nothing tricky. But
Listing 1 is a simple program. Nothing tricky. But
notice that I print the dimensioned variables in Lines
70-130 and then assign values to them in Lines 140-
190. I am assuming the variables have valid contents
before changing them! The only important restriction
here is to type the line containing the DIM
statement firsl. It doesn't have to be the first line
statement first. It doesn't have to be the first line
in the program. Just make sure it is the first line
typed.
The Atari Basic variable sy mbol table is con­
The Atari Basic variable symbol table is con
structed when each line is typed in, , not when the program
is run. Later we will need to find the locations
of the string variables in the table . This is
tions of the string variables in the table. This is
easier if they are the first variables present. For a
more complete discussion of the symbol table, see the
text in the box.
text in the box.
50 DIM A$(10),B(2 , 3)
50 DIM A?(10),B(2,3)
70 ? A$ AS
80 FOR 1=0 TO 2
80 FOR 1=0 TO 2
90 FOR J =0 TO 3
90 FOR J = 0 TO 3
1100 PRINT B{I,J), B( 110 NEXT J
120 PRINT
130 NEXT I
14~ ? "STRING=";:INPUT A$
140 ? "STRING=";:INPUT AS
150 15~ ? "I=";:INPUT I
160 IF 1=9 THEN 200
160 IF 1=9 THEN 200
170 17~ ? "J=";:INPUT "; : I A:B(I,J)=A
, 190 GOTO 150
190 GOTO 150
200 END
50 DIM A$(10),B(2,3)
70 ? A$
110 NEXT J
1120 PRINT
130 NEXT I
140 14~ ? "STRING=";:INPUT ";: INPUT AS A$
1501 5~ ? "I=";:INPUT I
160 IF 1=9 THEN 200
Al Baker
2327 S S. Westminster
Wheaton, IL 6O187
210 A=A+82
220 POKE 141,INT(A/256):POKE , 140,A-PEEK(141)*256141 230 CSAVE
procedure won't work.
AI Baker
Wheaton, IL 60187
Suppose the program is already written and you
didn't type the DIM statement first. Write your
program 10 to tape using the command LIST"C". Type
NEW. Now type the DIM statement from your program
with the string variables first. Finally, reload
the program from tape with the command ENTER
"e". "C". Now the string variables are at the beginning
of the variable tables.
Protect the Dimensioned Variables
The next step is to fool Basic into treating the
dimensioned variables as part of the program. Also,
you have to add the code to let the program save
itself to tape. In an application, saving the program
to tape will be the final program option selected by
the user. In Listing 2 this is added to the program
in lines 200 through 230.
50 Dnt A$( 1 0) ,B (2 ,3)
80 FOR 1=0 TO 2
90 FOR J=0 TO 3
100 l~ ~ PRINT B(I,J),
110 NEXT J
130 NEXT I
1 60 IF 1=9 THEN 200
170 ? "J=" "J=";:INPUT ; :INPUT A: A:B(I,J)=A B(I , J)=A
190 GOTO 150
200 A=PEEK(140)+PEEK(141)*256
)*256
210 A=A+82
230 CSAVE
Locations 140 and 141 contain the address of the
end of the computer program. Program line 200 places
this address in the variable A. In line 210 we add the
size of the dimensioned variables. Each string variable
containss as many bytes as its dimension. Each
numeric array contains 6 times the number of
members of the array. The B array is 6x(2 + l)x(3 + 1)
= ~ 6x3x4 = ~ 72 bytes. Thus we had to add 10 + 72 or
82 to the end of the program in the example.
Now run the program and let the internal CSAVE
create a tape. Turn the computer off and then on.
Now reload the newly created program from tape.
For some reason this step is important. (I don't 't
know why.) If you do not use the new tape, this
procedure won't work.
Finish the program
We now have a program in memory which has an
invalid program - end pointer. See Sec the third listing.
Add lines 10 through 40 to your program. Make sure
that you use the correct number instead of 4' -82"
that you use the correct number instead of "-82"