null values

[Cagliostro]

Hi, I have a problem

use strict;
my $x;

if($x){print("x\n");}else{print("!x\n");}
if($x == 0){print("x == 0\n");}else{print("x != 0\n");}
if($x == "0"){print("x == \"0\"\n");}else{print("x != \"0\"\n");}
if($x == "00"){print("x == \"00\"\n");}else{print("x != \"00\"\n");}
if($x == ""){print("x == \"\"\n");}else{print("x != \"\"\n");}
if($x == " "){print("x == \" \"\n");}else{print("x != \" \"\n");}
if($x == "  "){print("x == \"  \"\n");}else{print("x != \"  \"\n");}

my %xx;

if($xx{'abc'}){print("xx{'abc'}\n");}else{print("!xx{'abc'}\n");}
if($xx{'abc'} == 0){print("xx{'abc'} == 0\n");}else{print("xx{'abc'} != 0\n");}
if($xx{'abc'} == "0"){print("xx{'abc'} == \"0\"\n");}else{print("xx{'abc'} != \"0\"\n");}
if($xx{'abc'} == "00"){print("xx{'abc'} == \"00\"\n");}else{print("xx{'abc'} != \"00\"\n");}
if($xx{'abc'} == ""){print("xx{'abc'} == \"\"\n");}else{print("xx{'abc'} != \"\"\n");}
if($xx{'abc'} == " "){print("xx{'abc'} == \" \"\n");}else{print("xx{'abc'} != \" \"\n");}
if($xx{'abc'} == "  "){print("xx{'abc'} == \"  \"\n");}else{print("xx{'abc'} != \"  \"\n");}

printf("x = {$x}\n");
$x = 0;
printf("x = {$x}\n");
$x = "00";
printf("x = {$x}\n");
$x = " ";
printf("x = {$x}\n");
$x = "  ";
printf("x = {$x}\n");

this is the output:

!x
x == 0
x == "0"
x == "00"
x == ""
x == " "
x == "  "
!xx{'abc'}
xx{'abc'} == 0
xx{'abc'} == "0"
xx{'abc'} == "00"
xx{'abc'} == ""
xx{'abc'} == " "
xx{'abc'} == "  "
x = {}
x = {0}
x = {00}
x = { }
x = {  }

The value of variables comes from a CGI application, so, I have to know if there was passed some string, some number, some string with spaces or some string with zeroes. How can I test this thing? In each situation what is different than another one, the test is the same, but behavior is different...

Ion Filipski

 

[ishnid]

You should have warnings turned on, which would have helped to pinpoint your problem. Everything enclosed in quotes is a string, and you're using numeric comparison (==), whereas you should be using 'eq' for all the string comparisons.

 

[duncdude]

I think this might help - although I can't understand the necessity of checking for $variable == 0 as this gives false positives:-

[b]#!/usr/bin/perl[/b]

$x = '"0"';
checkThisOut("x", "$x");

$xx{'abc'} = '" "';
checkThisOut("xx{'abc'}", "$xx{'abc'}");

sub checkThisOut {

  $variableName = shift;
  $toCheck = shift;
  
  if ($toCheck) {
    print "$variableName\n";
  } else {
    print "!$variableName\n";
  }
  
  if ($toCheck == 0) {
    print "$variableName == 0\n";
  } else {
    print("$variableName != 0\n");
  }
  
  @toCheckAgainst = ('"0"', '"00"', '""', '" "', '"  "');
  
  foreach $item (@toCheckAgainst) {
    if ($item eq $toCheck) {
      print "$variableName eq $item\n";
    } else {
      print "$variableName ne $item\n";
    }
  }
  
}

outputs:-

[red][tt]x
x == 0
x eq "0"
x ne "00"
x ne ""
x ne " "
x ne " "
xx{'abc'}
xx{'abc'} == 0
xx{'abc'} ne "0"
xx{'abc'} ne "00"
xx{'abc'} ne ""
xx{'abc'} eq " "
xx{'abc'} ne " "[/tt][/red]


Kind Regards
Duncan