It's not as tricky as it sounds, thanks to InStrRev().

This UDF will return a array of the string broken at the delimiter before the required length.

Both delimiter and length are option and default to "," and 80 respectively.

If you pass a blank string you will get an array back with a single blank element.

If there is not a delimiter within the specified length then the string is split at the first available delimiter.

Code:
Function ChopString($s,Optional $l, Optional $d)
	Dim $i
 
	; Handle optional parameters
	$l=CInt($l)
	If Not $l $l=80 EndIf
	If $d="" $d="," EndIf
 
	; Deal with null strings
	If $s="" Redim Preserve $ChopString[0] Exit 0 EndIf
 
	; Break out long string lengths
	While Len($s)>$l
		$i=InStrRev(Left($s,$l),$d)
		If $i<0 $i=InStr($s,$d) EndIf
		Redim Preserve $ChopString[UBound($ChopString)+1]
		$ChopString[UBound($ChopString)]=Left($s,$i)
		$s=SubStr($s,$i+1)
	Loop
 
	; Grab what's left of the string
	If $s<>""
		Redim Preserve $ChopString[UBound($ChopString)+1]
		$ChopString[UBound($ChopString)]=Left($s,$i)
	EndIf
 
	Exit 0
EndFunction


Parameters:
  • $s = String to split
  • $l = Maximum length of parts (Optional, default=80)
  • $d = Delimiter to break on (Optional, default=",")