https://bugs.freedesktop.org/show_bug.cgi?id=86386
Bug ID: 86386
Summary: A better Mid-function
Product: LibreOffice
Version: 4.2.7.2 rc
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: enhancement
Priority: medium
Component: BASIC
Assignee: [email protected]
Reporter: [email protected]
The Mid-function is less then optimal.
Problems are
- a negative length is treated like no length given
- a start position of 0 results in error 5
- a negative start positions returns !br0ken!!
Taking inspiration from the way ruby handles strings, I propose improvements as
follows.
- Mid should take negative length which runs from left to right
- it should take negative start positions which are counted to the left, from
the last position in the String i.e. the last Position is -1, the next to last
is 2 etc.. 0 is the first position before the start of the string, as is
-Len(ofthestring) - 1
For details please refer to the definition of the Middle-function below which
is largely backwards compatible to Mid, unless you count the throwing of errors
and "!br0ken!!" as intended behaviour. It might break programs which rely on a
negative length being treated as no length.
Sub MiddleDemo
Dim sText As String
sText = "abcdefghijkl"
Print "The Mid-function is " & Mid(sText, -1)
Print Middle(sText, 0, 3) 'the first two characters
Print Middle(sText, -1, -4) 'the last four characters
Call Middle(sText, 6, -3, "456") 'replace three characters counted to the left
from the sixth position
Print sText
End Sub
Function Middle(sText As String, Optional lStart As Long, Optional lLen As
Long, Optional sInsert As String) As String
If IsMissing(lStart) Then lStart = 1
Dim lLenText As Long
lLenText = Len(sText)
If IsMissing(lLen) Then
If lStart >= 0 Then
lLen = lLenText 'get whole text up to the end of the string
Else
lLen = -lLenText 'get whole text up to the start of the string
End If
End If
Dim lMidStart As Long 'start of the string to return, we intend to use the
orginal Mid-function
If lStart < 0 Then
lMidStart = lLenText + 1 + lStart 'convert negative position to corresponding
positive position
Else
lMidStart = lStart
End If
Dim lMidLen As Long 'length of the string to return
If lLen < 0 Then 'the string to return is on the left to lMidStart
lMidStart = lMidStart + 1 + lLen 'start of the string
lMidLen = -lLen
Else 'the string to return is right to lMidStart
lMidLen = lLen
End If
If lMidStart < 1 Then 'start still negative,
lMidLen = lMidLen + lMidStart - 1 'length must be shortened, so that we cab
use thr original Mid-function
lMidStart = 1 'the string to return starts from the first position
End If
'if lMidLen isn't positiv, return an empty string
If lMidLen < 1 Then 'we can't give a negative length to the original Mid,
because ist would return the whole string sText
Middle = ""
Else 'ready to use the original Mid
Middle = Mid(sText, lMidStart, lMidLen)
End If
If IsMissing(sInsert) Then Exit Function 'don't change the string sText, so we
are done
sText = Left(sText, lMidStart - 1) & sInsert & Mid(sText, lMidStart + lMidLen)
End Function
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