So, here comes a quick trivia question:
What shall this little script output?
my @array = undef;
if(@array) {
print "defined\n";
} else {
print "undefined\n";
}
To my own surprise, the output was this:
defined
I couldn't believe what I saw at first. I just spotted a similar 'bug' in my code where one of my subroutines would return 'undef' in an array assignment statement. My consequent if checks on that array thus failed (at least didn't work as I thought they should).
The trick here is that setting @array to undef doesn't really destroy or 'undefine' that array variable. It instead sets the first element of the array to 'undef'! Therfore, the array _does_ exist or rather it's size is positive (>0), albeit it's first item is 'undef'. At least that's the only way I can manage to explain this wierd behavior.
Setting array to '()' (empty array) on the other hand makes things work:
my @array = ();
if(@array) {
print "defined\n";
} else {
print "undefined\n";
}
"There is no system but GNU, and Linux is one of its kernels." -- Confession of Faith
|
-
Are you posting in the right place? Check out Where do I post X? to know for sure.
-
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
<u> <ul>
-
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).
-
Want more info? How to link
or How to display code and escape characters
are good places to start.
|