Checking for Arguments before Usage?

nickcave25 has asked for the wisdom of the Perl Monks concerning the following question:

Is it required (or at least a good idea) to confirm that arguments feeding into subroutines are actually specified?

If so, how do you do it?

This situation is giving me problems:


foreach $message (@logmessages)
{
    LI(); 
    Strong($message);
}    


sub LI
{ 
    #if (@_) {my($inputValue) = $_0;}
    
    print "<LI>$_0\n";

}
[download]

Note: the commented-out statement is my attempt at a solution for this quandry. And here's the quandry:

When this executes, I get a "Use of initialiized value" error regarding the reference to $_0 in the print command within the definition of LI().

I want to be able to both feed arguments into LI() (when I call it from other places) and _not_ feed in arguments (as in this instance).

Is there a way to set up that subroutine to allow for both cases?
TIA.

Comment on Checking for Arguments before Usage? Download Code

Replies are listed 'Best First'.
Re: Checking for Arguments before Usage? by chromatic (Archbishop) on Feb 09, 2000 at 23:41 UTC
In this case, you might also leave the subroutine if you don't get any arguments: `return unless @_;`	[reply] [d/l]
Re: Checking for Arguments before Usage? by btrott (Parson) on Feb 09, 2000 at 23:28 UTC
Or, if 0 is a valid value for the input to the subroutine (ie., you don't want to set $inputValue to the default if 0 is the arg), use: `my $inputValue = defined $_[0] ? $_[0] : "default value";` [download]	[reply] [d/l]
Re: Checking for Arguments before Usage? by nickcave25 (Acolyte) on Feb 10, 2000 at 04:50 UTC
Thanks! I jotted down all 3 suggestions into the margin of page 95 of the llama book.	[reply]
RE: Checking for Arguments before Usage? by nickcave25 (Acolyte) on Feb 09, 2000 at 17:45 UTC
But I guess my question still stands: Do you need to check for the presence of arguments before plugging them into the machinery within your subroutines?	[reply]
Re: Checking for Arguments before Usage? by nickcave25 (Acolyte) on Feb 09, 2000 at 17:49 UTC
Make that `$_[0] instead of $_0`.	[reply] [d/l]
Re: Checking for Arguments before Usage? by Anonymous Monk on Feb 09, 2000 at 23:23 UTC
on your commented out line, try the following `my $inputValue = $_[0] \|\| "some default value in case of no argument" +;` [download] If there is a chance that your argument won't exist, always set up some kind of error checking or set a default value. the code i've used is a shorter version of an if:else construct.	[reply] [d/l]