[Gambas-user] EOF problem

[Doriano Blengino]

Ed & Clare Kelm ha scritto:
I was feeling that my words could be seemed not appropriate. In fact, I 
added that "our friends know what they are doing", and labeled those 
things as "very little thing", knowing in my mind that was experimental 
code  to debug some strange behavior. Sorry for that. I did that to 
stress that this code:
> Hi all:
>
> A couple of comments about the discussions below:
>
> 1.  The test program was written with EOF at the start, because the
> actual program I am working on has this structure, for reading in
> multiple lines of text:
>
> WHILE NOT EOF(tfile)
>      (bunch of code for reading the lines in and putting the data in the
> proper places)
> WEND
>
> CLOSE #tfile
>    
has nothing wrong for me. And if the previous code "was written with EOF 
at the start", it is simply because there is no other way to go. Happy 
to know that file.load() seems to solve - anyway if that EOF has a bug, 
it is a harmful one.

Regards,
Doriano
> When that failed, I wrote the test program to see if I was actually
> sometimes getting an EOF immediately after opening the file, since the
> first thing WHILE does is test EOF.
>
> 2.  Clearing label1 after every button click is just a little
> insurance.  Given that things weren't working as expected, I wanted to
> make sure what I saw in label1 was new info, not something left from the
> previous button click.  I know that shouldn't be necessary, because the
> IF-THEN-ELSE structure will always write to the label - but then there
> shouldn't be an immediate EOF either.
>
> 3.  Using Fname like that is just a little habit I've developed.  It
> allows me to try a different file by commenting out one setting of Fname
> and writing a new one, without erasing the previous one.  And it makes
> the OPEN statement more compact and easy to read.  It is also sometimes
> useful to put such equates all in one place, so it's easy to find and
> change parameters, rather than rummaging around in the code.  You are
> correct, it is sort of a waste if I am only using the variable once.  In
> my actual program, Fname also gets used when the database gets modified
> and the file then has to be re-written.
>
> I am not a professional programmer, so I'm sure I have some ways of
> doing things that make professionals cringe!
>
> Thanks again for thinking about my problem!
>
> Regards,
>
> Ed K.
>
> Doriano Blengino wrote:
>    
>> Les Hardy ha scritto:
>>
>>      
>>> Doriano Blengino wrote:
>>>
>>>
>>>        
>>>> Les Hardy ha scritto:
>>>>
>>>>
>>>>
>>>>          
>>>>> Hi Ed,
>>>>> I figured it out.
>>>>> First of all, depending how the text file was emptied/created, the
>>>>> contents may not be truely empty.
>>>>> Gedit for example leaves the 0A (end-of-line) character in the 'empty'
>>>>> file. This is recognised by eof() as a character, so, end-of-file is not
>>>>> found.
>>>>> I am not sure if this can be considered a bug in Gambas, but it does
>>>>> mean an eof() is only good for preventing read errors, and is not
>>>>> reliable for testing if a file is empty.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>            
>>>> Just breaking in to say that a file with a EOL in it is not an empty
>>>> file - it is a file with an empty line in it...
>>>>
>>>>
>>>>
>>>>          
>>> Your correct, I agree completely, but the original code Ed supplied, '
>>> IF Eof(tfile) ' cannot work , as it checks eof before a read.
>>> When I saw he was using eof() that way, and knowing empty files are not
>>> always empty, I thought I had found his problem, so I just added a bit
>>> of code that should have got around it.
>>>
>>> I am sure you will agree, that, whatever other problems he may have,  he
>>> needs not to use eof() the way he is.
>>>
>>>
>>>        
>> Here is the original code. I think it is perfectly right:
>>
>>      
>>> PUBLIC SUB Button1_Click()
>>>
>>>     DIM tfile AS File
>>>     DIM Fname AS String
>>>
>>>     Fname = "/home/us/Documents/testdat.txt"
>>>
>>>     tfile = OPEN Fname FOR READ
>>>
>>>     label1.Text = ""
>>>
>>>     IF Eof(tfile) THEN
>>>        label1.Text = "EOF"
>>>     ELSE
>>>        LINE INPUT #tfile, label1.Text
>>>     END IF
>>>
>>>     CLOSE #tfile
>>>
>>> END
>>>
>>>
>>>
>>>        
>> If eof() is not checked *before* reading, then when? I see only two
>> things I would not do (but it depends a lot). First, why use the "fname"
>> variable, if it is used only once... second, why set label1.text if that
>> .text will be anyway written shortly later?
>>
>> But, apart from these two very little things, that can also have some
>> good reason, the rest of the code is the only possible, I think. Note
>> also that label1.text can get 3 different values: "EOF" is the file is
>> empty; "" if the first line of the file is empty; something else if the
>> first line of the file contains some data. These three cases cover all
>> the cases we talked about (empty and not empty files), and I think our
>> friends know what they are doing.
>>
>> Of course I may be wrong, but that use of eof() seems to me fully ok.
>>
>> Regards,
>>
>>
>>      
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