Getting substring to react sanely to end of index?

Hi,

Is it possible to somehow force substring to just return what it can
if its asked to substring more of a string than there is remaining.

Eg 'this is a string' is 16 characters long, imagine its assigned to
variable $a.

$a.substring(0,4) would return 'this '

$a.substring(10,3) would return 'str'

$a.substring(14,4) would throw an exception because it causes
substring to seek beyond the string boundary. Ideally what would
happen is it returns 'ng'. A substring referencing a range totally
outside of teh boundary is fine to throw an exception, that can be
dealt with.

Am I just barking up the wrong tree? Should I be dealing with this
programmatically?

Cheers
Richard

Richard Price wrote: $a.substring(14) will get the remainder of the string. That what you
were looking for or am I off?

Marco

--
Microsoft MVP - Windows PowerShell
http://www.microsoft.com/mvp

PowerGadgets MVP
http://www.powergadgets.com/mvp

Blog:
http://marcoshaw.blogspot.com

Close but no milkshake - basically I want a way to be able to get a
substring without necessarily knowing that the end of the string is
near - I'm dealing with variable length records, where I can be sure
of the maximum length, but not that the actual length is always the
maximum length, so I hit the end of the string unexpectedly.

I've written a very basic 'sane' get-substring function which does
what I wish -

## Return a substring (sanely)
function Get-SubString( [string] $value, [int] $startOfRange, [int]
$numOfChars )
{
## How long is the string
$strLength = $value.length

## Last index in string (index starts from 0, string length starts
from 1)
$strLastIndex = ($strLength - 1)

## Get number of characters in range (add one to include current
character)
$rangeLength = ($strLastIndex - $startOfRange) + 1

## Check to ensure number of characters required
## does not exceed characters available in string
if ( $numOfChars -gt $rangeLength )
{
## return what we can
$numOfChars = $rangeLength
}

## Check to see if the first index is within string
if ( $startOfRange -gt $strLastIndex )
{
throw "Start index exceeds end boundary"
}
if ( $startOfRange -lt 0 )
{
throw "Start index exceeds start boundary"
}

## Do the sub string!
$value.substring($startOfRange,$numOfChars)
}

Passing an index either greater than or less than the string length
(-1 or 25 in the original string) throws an exception that can be
handled, otherwise it returns either exactly the number of characters
asked for, or as many as left in the string.

Maybe that gives a better idea of what I was asking?

Cheers
Richard

Hi Richard,


You can right pad $a to the total of 14+4:

PS 55> ("{0,-18}" -f $a).substring(14,4)
ng

but this returns additional two spaces on the right side:

PS 57> ("{0,-18}" -f $a).substring(14,4).length
4


So, add a trim() call to remove the trailing spaces:


PS 56> ("{0,-18}" -f $a).substring(14,4).trim()
ng



---
Shay Levi
$cript Fanatic
http://scriptolog.blogspot.com

Richard Price wrote: I think I got you now...

You also want to handle stuff like this also:

PSH>$string
this is a string
PSH>$string.substring(20)
Exception calling "Substring" with "1" argument(s): "startIndex cannot
be larger than length of string.
Parameter name: startIndex"
At line:1 char:18
+ $string.substring <<<< (20)
PSH>

I don't see any other way myself at this time. You could spend time
trying to determine if an exception occured, but I think you'er way is
cleaner.

Marco