Re: A83: String output and operations


Re: A83: String output and operations

In a message dated 12/11/99 1:23:55 PM Central Standard Time, writes:

>  How do I make system strings (Str1-Str0) in asm? I
>  also want to do operations on the strings, like adding
>  and extracting subsets. In other words, the equivelant
>  of a basic program like this:
>  :"E"->Str1
>  :"0123456789ABCDEF"->Str2
>  :Sub(Str2,4,1)+Str1->Str1
>  :Disp Str1
>  (Output: 3E)
>  Is this possible to do, or is there somthing different
>  I could use that would be faster smaller, etc.
>  =====
>  Cyrus Collier, clarinet lord.
>  a.k.a. "The Virus"

It is better to avoid using OS Variables for stuff like this. Instead just 
use byte arrays of data that represents string data for you. To do that, you 
would have a Label with a ".db" statment, and your values following it, then 
a terminating '0' like so...

    .db "E",0
    .db "0123456789ABCDEF",0
    .db 0,0,0,0,0,0,0,0,0,0

I whipped up a routine for substring manipulation:

; Input: HL -> Source String, DE -> Destination String  
;   B = Position in Source String to Start, C = # of Bytes to Copy
    dec b
    jr z, Now_Copy_String
    inc hl
    DJNZ Find_Start_Loop
    ld b, 0
    ld (de), 0
Here is an example on how to use that...

    ld hl, String2
    ld de, String3
    ld bc, 4*256+5
    call Substring_Copy

and after that sequence, the memory at the label 'String3' will look like 

    .db "34567",0,0,0,0,0

I suggest that you not put your destination string directly in your program 
though, incase you accidentally overwrite some data later past the string. 
You should put it in Ram instead, and give yourself enough room to work with 
like so:

#define     TempString  Savesscreen+0
#define     NextVar     Savesscreen+25

And that will open up 25 bytes to store your string data. To display the 
string, you would use the _puts or _vputs romcalls. You can learn about how 
to do that in the AsmGuru tutorial set or any other tutorial out there. I 
hope I could have been of help, cya...