CODEWITHSUNDEEP
perl
jason dancks
jason dancks

Reputation: 1142

perl: Use of uninitialized value $file in concatenation (.) or string

The error occurs in a custom perl module for reading in a file. This uses CGI so the error messages get displayed in the browser.

my $check = CreateExam->new("exam2.txt","grades.txt");
$check->readexam();

CreateExam.pm:

sub new {
    my ($class,$file,$grades) = @_;
    print "<p>in new: file: $file, grades: $grades</p>\n";
    return bless {'file'=>$file,'gradefile'=>$grades},$class;
}

sub readexam {
    my $self = shift;
    print "<p>in readexam File: $self->{'file'}</p>\n";
    if (defined($self->{'file'})) {
        my $self->{'questions'} = [];
        my $count = -1;
        my $file = $self->{'file'};
        open(my $handle,"<$file") or die "<p>it was the open. File: $file</p>";
        while(<$handle>) {

ouput:

in new: file: exam2.txt, grades: grades.txt

in readexam File: exam2.txt

Use of uninitialized value $file in concatenation (.) or string at /var/www/homeworks/hw10/CreateExam.pm line 35 (#1)

Software error:

<p>it was the open. File: </p> at /var/www/homeworks/hw10/CreateExam.pm line 35.

Software error:

[Sun Dec 21 14:30:31 2014] hw10.cgi: <p>it was the open. File: </p> at /var/www/homeworks/hw10/CreateExam.pm line 

[Sun Dec 21 14:30:31 2014] hw10.cgi: [Sun Dec 21 14:30:31 2014] hw10.cgi:
it was the open. File:

at /var/www/homeworks/hw10/CreateExam.pm line 35.

I had use warnings and use diagnostics. It seems strange that I get a part of the error message twice.

Upvotes: 0

Views: 1190

Answers (1)

TLP
TLP

Reputation: 67900

You create a new variable $self at this point in your code:

    my $self->{'questions'} = [];
    my $count = -1;
    my $file = $self->{'file'};

Then you try to access it and assign a value to another variable $file, which will become undefined. When you use my you create a new variable in the current scope.

So the answer is probably: Don't use my in this case. You have already used it once at the top of the sub.

However...

It is completely redundant to assign a new array ref to the key questions. Perl's autovivification can handle that, e.g. if you do push @{ $self->{questions} }, $foo, you will create an array ref.

Upvotes: 4

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