http://qs321.pair.com?node_id=289758


in reply to Tk question

The error messages speak for themselves. In line 46/124, $t doesn't appear to be defined at all, and it looks like there's something similar causing the "Not a Tk Object" error.

My best guess is variable clash - removing all those requires was a *good* thing (but check out modules and the use statement sometime soon), but I reckon there are variables in the subs called $t somewhere that aren't localised...are you using strict & warnings? If not, do. They should be able to help you catch errors like this.

Cheers, Ben.

Replies are listed 'Best First'.
Re: Re: Tk question
by perl_seeker (Scribe) on Sep 10, 2003 at 06:01 UTC
    Hi,
    thanks for the reply.I am a bit confused.In the first section of code I have a text widget defined like this: 
    my $f = $mw->Frame->pack(-side => 'top', -fill => 'x');
my $t = $mw->Scrolled("Text",-font=>"{arial} 12 {bold}")->pack(-side =
+> 'bottom', -fill => 'both', -expand => 1);

    [download]
    Then I have a number of subroutines where $t is used again. These subroutines are bound to buttons which
    are defined in the frame above with stmts like: 
    $f->Button(-text => "Display", -command =>\&tged)->pack(-side => 'righ
+t'); 

sub tged {
@chars=$t->get('sel.first','sel.last');  
#print "\nSelected word:";
#print @chars;
  }
1;

    [download]
    In the sub &tged, the get stmt should read characters within the text widget defined initially using $t.If I use
    "my $t" within this sub and localise it, we wont be referring to the first $t defined outside the sub.Is that right?

    These subs also use $t again and need to refer to the text widget define initially using: 
    my $t = $mw->Scrolled("Text",-font=>"{arial} 12 {bold}")->pack(-side =
+> 'bottom', -fill => 'both', -expand => 1);

sub replace1{
.
.

$t->insert('sel.first',"$chosen1");    
.
.
}
1;

sub replace2{
.
.
$t->insert('sel.first',"$chosen2");
.
.
}
1;

sub replace3{
.
.
$t->insert('sel.first',"$chosen3");
.
.
}
1;                                           
 
sub addit{  
.
.
@addword=$t->get('sel.first','sel.last'); 
.
.
}
1;

    [download]
    I'm not sure where we should use "my", and where we should not.Turning on use strict gives no message about $t.
    The sub &tged works on the first button click, and does not work therafter.The other subs are not working at all.
    Please help.
    Thanx :)
[reply]
[d/l]
[select]
      OK - maybe my first guess was wrong... :)

      If I use "my $t" within this sub and localise it, we wont be referring to the first $t defined outside the sub.Is that right?
      Yes - that's right. I thought maybe you were using $t for some other purpose, but it would appear not.

      I'm not sure where we should use "my", and where we should not
      Check out the section on 'scope' in whatever perl books/docs you have. 'my' declares a variable within the 'current scope' - if that's in a sub (or any pair of braces),it's gone when you exit the sub. If, on the other hand, it's in the 'main body' of your code, it's global oops - I mean file scoped...ermm..global to your file...ermm...you know what I mean - see the AM posting below... . That is generally a Bad Thing.

      Turning on use strict gives no message about $t.
      Does it give messages about other things? What about use warnings? Fix these, and your problem may possibly go away.

      I haven't any more specific ideas, but here are a few general suggestions.

      • use strict; use warnings;
      • Don't use globals if you can help it. Pass arguments to subroutines instead - this helps your code become more 'general'
      • use strict; use warnings;
      • Refactor and tidy up. sub replace1,sub replace2 etc. look like they should be candidates for a single sub, with the replace string (and probably the text widget as well) passed in as a parameter.
      • use strict; use warnings;
      • Debug. Lots. Print out the values of $t after you initialise it, before you use it, after you use it etc. Check they're all the same type/memory address.
      Hope this helps, Ben.
[reply]
[d/l]
[select]
        'my' declares a variable within the 'current scope' - if that's in a sub (or any pair of braces),it's gone when you exit the sub. If, on the other hand, it's in the 'main body' of your code, it's global. That is generally a Bad Thing.
        That makes it sound like using "my" at global scope is a Bad Thing. Shurely not?
[reply]
        Hi :)
        It was $t which was causing the problem.I had declared it using 
        my $t = $mw->Scrolled("Text",-font=>"{arial} 12 {bold}")->pack(-side =
+> 'bottom', -fill => 'both', -expand => 1);

        [download]
        i.e. global to the file so these statement later 
        for($t=0;$t<$lthree;$t++)
 {
 if($mpart=~/$three[$t]/)

        [download]
        caused the problem.Here I had declared $t without "my".This portion of code was earlier in a separate
        file.I did not notice this bit earlier.
        Thanx :)
[reply]
[d/l]
[select]
        Hi :),
        I posted a reply before, but strangely it hasn't appeared on this page.It was $t causing all the problem.
        Initially $t was declared global to the file: 
        my $t = $mw->Scrolled("Text",-font=>"{arial} 12 {bold}")->pack(-side =
+> 'bottom', -fill => 'both', -expand => 1);

        [download]
        Then this bit of code, (which was earleir in a separate file) caused all the trouble.$t was declared without a my. 
        for($t=0;$t<$lthree;$t++)
{

        [download]
        Thanx,
        :)
[reply]
[d/l]
[select]
        ...'main body' of your code, it's global...
        Sorry, but it is not. Lexicals do not have global scope. What you are referring to is called file scope.
[reply]

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