From: Robert Klemme <bob.news@...>
Date: 2005-01-20T21:21:00+09:00
Subject: Re: Confused about variable "declarations"


"Graham Nicholls" <graham @rockcons.co.uk> schrieb im Newsbeitrag
news:1106221017_4840@surge1-maxim.com...
>
> Page 14 of the new Pickaxe book says (amongst other things):
>
> "Note that we didn't have to declare the variable 'result'; it sprang
into
> existence when we assigned to it."
>
> This was my understanding, but I keep seeing this sort of thing:
>
> ./duprop:136:in `find_pcap_offset': undefined local variable or method
> `offset' for #<Pcap_entry:0x40280794> (NameError)
>
> when I run this:
>
> offset=line.split()[1].to_i
>
> Its easily fixed: I assign 0 to offset earlier in the method:
>
> def find_pcap_offset  # Find the offset to the pcap entry for
printer_name
>     found=false
>     offset=0         # <- This fixes things.
>     begin
>       pcap_file=File.open(@pcap_fname)
>     rescue IOError
>       print("can't open pcap file #{@pcap_fname}\n")
>       exit(BAD_PCAP_FILE)
>     end
>     # OK, now find the pcap entry
>     pcap_file.each_line() do |line|
>       if line.match(@printer_name)
>         print("Found printer #{@printer_name} in [#{line}]\n") if $debug
>         found=true
>         offset=line.split()[1].to_i
>         break

Is this really the complete example?  Because from what I see 'offset' is
not read accessed here.  Which line causes the error?  Maybe you print out
'offset' after the each_line loop and no line matched.

And btw, I'd rearrage the code like this (I know that you don't need to
because of exit but if exit changes behavior i.e. not really exiting the
system you might see surprising results):

def find_pcap_offset  # Find the offset to the pcap entry for printer_name
    found=false
    offset=0         # <- This fixes things.
    begin
      pcap_file=File.open(@pcap_fname)

      # OK, now find the pcap entry
      pcap_file.each_line() do |line|
        if line.match(@printer_name)
          print("Found printer #{@printer_name} in [#{line}]\n") if $debug
          found=true
          offset=line.split()[1].to_i
          break
          ...
        end
        ...
      end

    rescue IOError
      $stderr.print("can't open pcap file #{@pcap_fname}\n")
      exit(BAD_PCAP_FILE)
    end

Or leave the exception handling completely out here.  IHMO the exception
is meaningful enough:

13:17:42 [otrs-1006999]: ruby -e 'def find_pcap_offset() File.open("x") {}
end; find_pcap_offset'
-e:1:in `initialize': No such file or directory - x (Errno::ENOENT)
        from -e:1:in `open'
        from -e:1:in `find_pcap_offset'
        from -e:1

> Now I hate to do this - partly at least 'cause its clear evidence I
don't
> understand something!

The error can only occur if you read access the var before writing it.

Kind regards

    robert