Re: DATA command, did I find a bug or a feature

Nice find! Clearly a feature. :)

I tried looking through the disassembly (VIC-20, but it's the same), and 
without analyzing it in detail, it looked like there was simply no 
validation of what's between commas, or after the last one in the 
statement. It's handed over to floating-point conversion, which looked 
like it initialized the value to 0 and then immediately terminated when 
encountering an empty string.

I wondered first why it doesn't accept "A=", but LET, unlike DATA, does 
expression evaluation, so it may not accept an empty string.

The MS Basic manuals don't mention this, and neither does the first CBM 
BASIC manual I found, which was more or less a verbatim copy of the MS 
one. However, the C64 user's guide says "If two commas have nothing 
between them, the value will be READ as a zero for a number, or an empty 
string" (page 118)

/Hans

On 2021-09-09 10:15, Baltissen, GJPAA (Ruud) wrote:
>
> Hallo allemaal,
>
> I’m busy writing my own OS and BASIC meant to run on my Commodore 
> PC20-III and written in ML. Checking the behavior of DATA and READ on 
> my C64 I ran into this:
>
> 1 data 1,2,
>
> 2 data 3,4
>
> 3 read a,b,c,d
>
> 4 print a,b,c,d
>
> run
>
> 1    2    0    3
>
> Notice the sole comma at the end of line 1. I more or less expected an 
> error during the run because no data can be found after that comma but 
> you can see the result. I thought to be smart and to run this little 
> program on an IBM 5150 but with the same result. Then it struck that 
> CBM BASIC was written by Microsoft as well. And I don’t have other 
> machines (or even an emulator) at hand where I could test this.
>
> My question: did I run into a bug or is this supposed to happen?
>
> With kind regards / met vriendelijke groet, Ruud Baltissen
>
> http://www.baltissen.org <http://www.baltissen.org/>
>
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