[Coco] Returning a string to basic ?

[Bob Devries]

Rogelio wrote:

> As noted, manipulating these values once a string variable has been 
> defined
> we can put whatever we want in the string variable... as long as it is at
> most 255 bytes long ;-)

Don't forget to terminate the string with a $FF byte, and put the length of 
the string back into the first byte.

Regards, Bob Devries
Dalby, QLD, Australia

----- Original Message ----- 
From: "Rogelio Perea" <os9dude at gmail.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Wednesday, September 21, 2011 8:11 AM
Subject: Re: [Coco] Returning a string to basic ?


> On Tue, Sep 20, 2011 at 5:43 PM, Arthur Flexser <flexser at fiu.edu> wrote:
>
> I'm going from hazy memory on this...
>>
>> I'm assuming the string is at a known address and has a known length.
>>
>> What you need to do is this:
>>
>> Define a dummy string in the Basic program with some statement like 
>> S$="A".
>>
>> Then use the Basic VARPTR function to find the address of Basic's
>
> pointer to the string:  ST=VARPTR(S$).
>>
>> At the address now contained in ST is a 5-byte string specifier.  The
>> first (I think) byte is the string length, and the 3rd and 4th (?)
>> contain the address of the string data.
>> (The other 2 bytes of the 5-byte identifier are unused.)
>>
>> Using POKEs, you can modify these 3 bytes to insert the length and
>> address of the string you want Basic to know about, which will then be
>> referenced by S$.
>>
>> Hope that does the trick for you!
>>
>> Art
>>
>
> Elaborating:
>
> PEEK(ST) will return the length of the string variable
> PEEK(ST+2) will be the MSB of the variable first character address in 
> memory
> PEEK(ST+3) will be the LSB of the variable first character address in 
> memory
>
> Examining RAM locations after the MSB & LSB are calculated up to the 
> length
> of the string will reveal the variable contents.
>
> As noted, manipulating these values once a string variable has been 
> defined
> we can put whatever we want in the string variable... as long as it is at
> most 255 bytes long ;-)
>
>
> -- RP
>
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