default value for a scalar

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

Hi experts, I have two values that I am passing to a subroutine. If they are empty I want to give them a default value of zero. How should I change what I am doing because I keep getting the complaint: "Use of uninitialized value in length..." What I am trying to accomplish by the subroutine is to only print the line if there is a value greater than zero in either of the scalars. This how I call the subroutine:

print_if(\*FH,'AXS ',$aOrder->{rx_OD_Axis},$aOrder->{rx_OS_Axis});
[download]

This is the subroutine:

sub print_if {
  my($FH, $orderKey, $odVal, $osVal) = @_;
  #if (!defined $odVal) {$odVal = 0;}
  #if (!defined $osVal) {$osVal = 0;}
  if (!(length($odVal) > 0)) {$odVal = "0";}
  if (!(length($osVal) > 0)) {$osVal = '0';}
  if ($odVal > 0 || $osVal > 0) {
    print $FH $orderKey.' '.$odVal.' '.$osVal."\n";
  }
}
[download]

Thank you for your help. Warm regards,

Comment on default value for a scalar Select or Download Code

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Re: default value for a scalar by pc88mxer (Vicar) on Apr 19, 2008 at 20:56 UTC
I understand your issue now... the arguments to `$osVal` and `$odVal` can either be `undef` or the empty string when the default value should be used for them. In that case, a convenient solution is the `\|\|=` operator: `$odVal \|\|= 0; $osVal \|\|= 0;` [download]	[reply] [d/l] [select]
Re^2: default value for a scalar by rightfield (Sexton) on Apr 19, 2008 at 22:08 UTC
Thank you pc88mxer your solution worked first time. Warm regards.	[reply]
Re: default value for a scalar by jwkrahn (Abbot) on Apr 19, 2008 at 21:20 UTC
Change: `my ( $FH, $orderKey, $odVal, $osVal ) = @_;` [download] To: `my ( $FH, $orderKey, $odVal, $osVal ) = map $_ \|\| 0, @_[ 0 .. 3 ];` [download]	[reply] [d/l] [select]
Re^2: default value for a scalar by rightfield (Sexton) on Apr 19, 2008 at 22:07 UTC
Thank you jwkrahn your solution worked as well as the first and I learned a new function. Warm regards	[reply]
Re: default value for a scalar by mscharrer (Hermit) on Apr 20, 2008 at 10:22 UTC
like already posted by pc88mxer you can set default values with the `\|\|` operator which has the drawback that it not only triggers the default value when the variable is unset, i.e. undef, but also for all other boolean false values like: 0, "" and "0". Because your default value is 0 this doesn't matter because all of this values would be converted to 0 anyway, but a warning would be raised. E.g. when the the function would be called as `print_if(0)` the given 0 would be overwritten by your default 0, which no consequences of course. If your default value would be now 1 the call `print_if(0)` would be changed to `print_if(1)`. To avoid this use: `$odVal = defined $odVal ? $odVal : 0; $osVal = defined $osVal ? $osVal : 0;` [download] In Perl 5.10 there is now the `//` operator which does exactly this, so you could write it so: `$odVal //= 0; $osVal //= 0;` [download] Then, of course, your code wouldn't run with Perl <5.10, so don't use this just now. You also could change the code posted by jwkrahn from `my ( $FH, $orderKey, $odVal, $osVal ) = map $_ \|\| 0, @_[ 0 .. 3 ];` [download] to `my ( $FH, $orderKey, $odVal, $osVal ) = map defined $_ ? $_ : 0, @_[ 0 + .. 3 ];` [download] Finally if you just like to remove the warning you could put a `no warnings 'uninitialized';` in your function. Then undef values would be taken as 0 without a warning.	[reply] [d/l] [select]