User Tools

Site Tools


String manipulation routines

Here is a set of routines to handle null-terminated character strings. Included is a small demonstration as to how they should be used. You will find routines to count the length of a string, copy a whole string, copy a string up to a predetermined offset, concatenate two strings and print a string. Take care to notice which pointer each routine utilizes.

The zero page locations used fall within the floating point accumulators of the BASIC interpreter and should be safe to use, while not performing floating point math. The majority of the strcat routine is adjusting the source pointer to match the length of the existing destination string. This is due to the fact that the second index register cannot be used for indirect indexing.

The routines have been thoroughly tested.

; various string manipulation routines by FMan/Tropyx

; all strings handled by these routines must be null-terminated, and their
; maximum length determined by the range of the index registers is 255 chars

	!to "str.prg",cbm	; compile using ACME

	src = $62
	dst = $64
	tmp = $66
	len = $68


; sample code for using these routines

	lda #<str1		; set address of dst string
	sta dst
	lda #>str1
	sta dst+1
	lda #<str2		; set src string
	sta src
	lda #>str2
	sta src+1
	jsr strcat
	jsr print		; uses the same dst pointer

str1	!pet "hello, ",0
	!fill 8			; insert work space
str2	!pet "world",13,0

; strlen - returns the length of a string in Y, preserves X
; (upon return, index register Y points to the terminator)

strlen	ldy #0
slena	lda (dst),y
	beq slenb
	bne slena
slenb	rts

; strcpy - copies a string from src to dst, preserves X

strcpy	ldy #0
scpya	lda (src),y
	sta (dst),y		; the store instruction does not change the
	beq scpyb		; Z flag and this copies the terminator too
	bne scpya		; maximum length of the string is 255 chars
scpyb	rts

; strncpy - copies a string up to the specified point set in 'len'

strncpy	ldy #0
sncpya	lda (src),y
	sta (dst),y
	beq sncpyb
	cpy len
	bcc sncpya
	lda #0			; terminate the destination when cutting
	sta (dst),y
sncpyb	rts

; strcat - concatenates src and dst, ie. adds dst to src - preserves nothing

strcat	jsr strlen		; get index to the end of the dst string
	lda src+1
	sta tmp+1
	lda src
	sty tmp			; subtract the length of the existing
	sbc tmp			; string from the source address, so that
	sta tmp			; the index will match
	bcs scata
	dec tmp+1
scata	lda (tmp),y		; copy source to the end of existing dst
	sta (dst),y
	beq scatb
	bne scata
scatb	rts

; print - outputs a string to screen (or to a channel specified using CHKOUT)

print	ldy #0
pra	lda (dst),y
	beq prb
	jsr $ffd2		; call CHROUT
	bne pra
prb	rts
base/string_manipulation_routines.txt · Last modified: 2015-04-17 04:34 by