in reply to Reading into array with sscanf

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11160631
use warnings;

my $save_fn = 'save.fn'; # NOTE

my @c_speed = (5, 8, 12, 8);
my $sfh;
  open($sfh, '>', $save_fn) or
        die "Unable to open file $save_fn : $!";
  print $sfh "@c_speed\n";
  close $sfh; # NOTE

#...
#
#The file contains a line that looks like "5 8 12 8\n"
#...

my $load_fn = 'save.fn'; # NOTE

my $lfh;
  open($lfh, '<', $load_fn) or
        die "Unable to open file $load_fn : $!";
#$rstring  = <$lfh>;  # Char speeds
#  ($c_speed[0], $c_speed[1], $c_speed[2], $c_speed[3]) = sscanf("%d %
+d %d %d", $rstring);
  # NOTE using ' ' instead of / / also removes the \n
  @c_speed = map $_ + 0, split ' ', <$lfh>; # NOTE force number

use Data::Dump 'dd'; dd @c_speed;

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Outputs: 

(5, 8, 12, 8)

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Replies are listed 'Best First'.
Re^2: Reading into array with sscanf
by colintu (Acolyte) on Jul 16, 2024 at 16:11 UTC

    Thanks for all the replies. The examples all work and I even understand them (after a bit of reading). However, I'm seeing some weirdness in my actual application. The c_speed variable is being used in a Tk widget as follows: 

    my $cs_e1   = $seg1_f->Entry(-textvariable => \$c_speed[0], -width => 
+4,
                                                -validate => 'all',
                                                -vcmd  => \&validate_s
+peed,
                                                -font => $med_font)->g
+rid(
                                                -row => 0, -column => 
+1,
                                                -sticky => "w");

sub validate_speed{
  my $val = shift;
  $val ||= 0;
  #get alphas and punctuation out
  if( $val !~ /^\d+$/ ){ return 0 }
  if (($val >= 0) and ($val <= 10)) {return 1}
    else{ return 0 }
}

    [download]

    When I use split I can print c_speed to the terminal and the values are there, the same as when I use my sscanf lines

      $rstring  = <$lfh>;
  ($c_speed[0], $c_speed[1], $c_speed[2], $c_speed[3]) = sscanf("%d %d
+ %d %d", $rstring);

    [download]

    BUT, the Tk Entry widget only sees the new values when using sscanf. When I use split the variable still retains it's old value. I'm assuming this is some widget weirdness - can anyone explain please?

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[d/l]
[select]

      Can you show some of the values that do not update?

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        As shown in the example I just posted the variable $c_speed[0] in the Entry widget doesn't update when the "split" version of load file routine runs, but it *does* update when the sscanf version runs. The entry box itself works. The whole application is 500 lines so I don't want to post that here.

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