I've run across a strange bit of behavior within DBI. When I set the 'LongTruncOk' parameter to true for a database handle and retrieve a long string it seems to insert null bytes between each character. For example, a string of '600' comes back as (in hex):

36 00 30 00 30

This pattern persists throughout the string. This does not occur if LongTruncOk is set to false.

Is this expected behavior that I'm simply ignorant of? I want it to automatically truncate strings that are too long, but not if my string gets trashed in the process.

The following code reproduces the problem. I'm working with an MS SQL Server if it matters.

#!/usr/bin/perl
use strict;
use warnings;
use DBI qw(:utils);

my $data;
my $host  = 'somehost';
my $query = <<'END';
  select
    someColumn
  from someDb.someSchema.someTable
  where id = someValue
END

$data = queryDb(
  'host'        => $host,
  'query'       => $query,
  'longTruncOk' => 1,  
);

print $data->[0][0], "\n"; #Output as ASCII
$data->[0][0] =~ s/(.)/sprintf("%x ",ord($1))/eg;
print $data->[0][0], "\n"; #Output as hex

sub queryDb {
  my %args = @_;
  my $connStr = 'DBI:ODBC:' . $args{host};
  my $dbh     = DBI->connect($connStr)
    or die "Couldn't connect to database: " . DBI->errstr . "\n";
  my $table = [];
 
  $dbh->{LongReadLen} = defined $args{longReadLen} ? $args{longReadLen
+} : 80;
  $dbh->{LongTruncOk} = defined $args{longTruncOk} ? $args{longTruncOk
+} : 0; #Note - this seems to change strings to UTF-16?
  
  my $sth = $dbh->prepare($args{query})
    or die "Couldn't prepare statement: " . $dbh->errstr . "\n";
  $sth->execute( @{ $args{params} } );
  while (my @row = $sth->fetchrow_array()) {
    push @$table, \@row;
  }
  
  return $table;
}
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