12.14.1. Problem

12.14.2. Solution

12.14.3. Discussion

Like built-ins, some of your module's functions generate warnings or errors if all doesn't go well. Think about sqrt: when you pass it a negative number (and you haven't used the Math::Complex module), an exception is raised, producing a message such as "Can't take sqrt of -3 at /tmp/negroot line 17", where /tmp/negroot is the name of your own program. But if you write your own function that die s, perhaps like this:

sub even_only {
    my $n = shift;
    die "$n is not even" if $n & 1;  # one way to test
    #....
}

then the message will say it's coming from the file your even_only function was itself compiled in, rather than from the file the user was in when they called your function. That's where the Carp module comes in handy. Instead of using die, use croak instead:

use Carp;
sub even_only {
    my $n = shift;
    croak "$n is not even" if $n % 2;  # here's another
    #....
}

If you just want to complain about something, but have the message report where in the user's code the problem occurred, call carp instead of warn. For example:

use Carp;
sub even_only {
    my $n = shift;
    if ($n & 1) {         # test whether odd number
        carp "$n is not even, continuing";
        ++$n;
    }
    #....
}

carp "$n is not even, continuing" if $^W;

The Carp module provides a third function: confess. This works just like croak, except that it provides a full stack backtrace as it dies, reporting who called whom and with what arguments.

If you're only interested in the error message from carp, croak, and friends, the longmess and shortmess functions offer those:

use Carp;
$self->transplant_organ( ) or
  $self->error( Carp::longmess("Unable to transplant organ") );

12.14.4. See Also