Optional parameter passing to a function??

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

Hi Monks!!

How can I pass optional parameters in a function? Here is my code.

print "Testing optional parametrs\n";
prog( 1,,,2,3);
print "End\n";

sub prog {
    my($a,$b,$c,$d,$e) = @_ ;
    
    
    print "a = $a\n";
    print "b = $b\n";
    print "c = $c\n";
    print "d = $d\n";
    print "e = $e\n";
}
[download]

In the above programme I want to keep two parameters optional, i.e., if user does not want to pass 2nd and 3rd parameter, then he/she simply call it like prog(1,,,2,3). But when I am trying to use like this the program output is a=1 b=2 c=3 d= e= , but my desired output is a=1 b= c= d=2 e=3. I know that if I call the prog function as prog(1,"","",3,4), I can get the desired output, but for optional parameter I have to put "", which is not desirable. Can anyone please tell me how I can get the fucntionality?

Thanks in advance.
-Pijush

Comment on Optional parameter passing to a function?? Download Code

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Re: Optional parameter passing to a function?? by davorg (Chancellor) on Aug 03, 2004 at 12:35 UTC
You would need to pass `undef` in the missing slots. `prog(1,undef,undef,2,3);` [download] But if you have optional parameters you'll be far better off passing named parameters using a hash. -- <http://www.dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply] [d/l]
Re: Optional parameter passing to a function?? by ccn (Vicar) on Aug 03, 2004 at 12:33 UTC
You can pass a hash as parameters list: `sub prog { my %args = ( a => 'default_a', b => 'default_b', c => 'default_c', d => 'default_d', @_ ); print "a => $args{a}\n"; print "b => $args{b}\n"; print "c => $args{c}\n"; print "d => $args{d}\n"; } prog( b => 1, a => 2);` [download]	[reply] [d/l]
Re: Optional parameter passing to a function?? by sweetblood (Prior) on Aug 03, 2004 at 12:40 UTC
I have written several subs that have optional parameters but have always put the at the end. <pseudo-code> `sub foo { my ($p1, $p2, $p3, $p4, p5) = @_; do { #something } if $p4; do { #something } if $p5; #etc }` [download] </pseudo-code> Then you can call your sub with 3,4,5 (or any number) of parameters or you can call your sub like: `prog(1,"","",2,3)` [download] or `prog(1,undef,undef,2,3)` [download] HTH Sweetblood	[reply] [d/l] [select]
Re: Optional parameter passing to a function?? by ysth (Canon) on Aug 03, 2004 at 19:38 UTC
The term for using a hash or pairlist that people have shown is "named parameters". Try searching here for many of the previous discussions and modules that help. (In the perl core, CGI is a not-for-the-faint-of-heart example of a bastardized positional/named parameter scheme.)	[reply]