title	perror - print error message
	include	asm.inc

	public	perror

	.data
	extrn	dgroup_segment:word

	.data?
errmsg_buffer	db	100 dup(?)


	.code
	extn	clear_strerror,get_strerror,fwrite,save_most,strcpy_limit

;;	perror
;
;	entry	DS:SI	optional message prefix
;	uses	AX
;
perror	proc
	call	save_most
	mov	es,dgroup_segment[bp]	; set destination pointer
	mov	di,offset errmsg_buffer
	lea	dx,[di+size errmsg_buffer-4] ; (-4 leaves room for ": " & \n)

	cmp	si,NULL_POINTER
	je	per1			; if no message prefix
	call	strcpy_limit		; else copy message prefix
	mov	ax,' :'			;  and ": "
	stosw

per1:	call	get_strerror
	jz	per2			; if no error string
	call	clear_strerror
	call	strcpy_limit

per2:	mov	ax,NEWLINE_CHARS	; append \n
	stosw

	mov	bx,stderr		; write text to standard error
	mov	ds,dgroup_segment[bp]
	lea	si,errmsg_buffer
	mov	cx,di			;  compute message byte count
	sub	cx,si
	call	fwrite
	ret
perror	endp

	end