From: rumpy@...
Date: 2008-06-21T05:13:12+09:00
Subject: Re: Problem with while loop.

Hi Stefano,


Quoting Stefano Crocco <stefano.crocco@alice.it>:

> On Friday 20 June 2008, rumpy@mrbitter.org wrote:
>> Hi,
>>
>>
>> I'd greatly appreciate feedback on the following code.
>>
>>
>> def create_files
>>      names_array = self.read_names #another method in my class
>>
>>      while names_array.length != 0
>>        name = names_array.pop
>>        File.open( name, "w" ) { |f| f.puts "File is no longer empty" }
>>      end
>>
>> x.create_files
>>
>>
>> Which results in:
>>
>> C:/Scripts/Ruby/file_gen.rb:34:in `initialize': Invalid argument - echo
>> (Errno
>>
>> ::EINVAL)
>>
>>          from C:/Scripts/Ruby/file_gen.rb:34:in `open'
>>          from C:/Scripts/Ruby/file_gen.rb:34:in `create_files'
>>          from C:/Scripts/Ruby/file_gen.rb:42
>>
>> The array contains the strings 'alpha' through 'foxtrot' and before
>> producing the error above the file 'foxtrot' is created. So the logic
>> works once before failing.
>>
>> When I pull this code out of the class definition it works perfectly
>> and creates
>> a file for every name in the array. What noob mistakes am I making?
>>
>>
>> Thanks,
>>
>> S.
>
> To understand what's going on, one should understand what the error
> Errno::EINVAL means. Unfortunately, the only explaination a very quick search
> returned is this:
> "Invalid argument. This is used to indicate various kinds of problems with
> passing the wrong argument to a library function."


Firstly, thank you very much for the feedback. I did also look for  
more info on Ruby errors. Not much luck finding details on  
Errno::EINVAL.


> I don't know what can be causing it. I tried passing non-string arguments to
> File.open, but I always got TypeError s, except when I tried passing an
> integer, which gave me an Errno::EBADF exception (I'm on linux, though, so
> maybe on windows that can give you another kind of error). At any rate, the
> first thing I'd try (maybe you've already done it) is to check that   
> indeed the contents of names_array is what you think it is, putting a
> p names_array just after creating it.


I did replace 'File.open( name, "w" ) { |f| f.puts "File is no longer  
empty" }' with 'puts name' and 'puts name.class' just to make sure.  
Sure enough all the array elements are neatly popped out and they are  
strings.


> If that doesn't give you a clue, you can rewrite the code in a more rubysh
> way. If I understand correctly, you're simply iterating on all the   
> elements of the array and the while loop and calls to pop are simply  
> there    > to know when to stop the loop. In this case, the whole  
> while loop can be      > replaced by this:


Your analysis of the code is correct.


> array_names.each do |n|
>   File.open(n, "w"){|f| f.puts "File is no longer empty"}
> end


I'll try this.


> The substance of the code shouldn't change (well, aside from the   
> fact that the array won't be empty at the end), but this should  
> ensure        > there is no mistake in the logic of the loop (I  
> can't see any, but you        > never know).
>
> Other than this, I don't know what else to suggest.
>
> I hope this helps


Thanks again for you time and suggestions.


> Stefano


Regards,

S.