fig04_18.pl

PERL语言资料 可以用于PERL程序设计

#!/usr/bin/perl
# Fig. 4.18: fig04_18.pl
# Demonstrating functions delete, exists and defined.

%hash = ( Karl  => 12,
          Joe   => 43,
          Shawn => 0,
          Paul  => 11, 
          Bill  => undef );

# obtain the list of hashKeys and display each key-value pair
@hashKeys = keys( %hash );

for ( $i = 0; $i < @hashKeys; ++$i ) {
   print "$hashKeys[ $i ] => $hash{ $hashKeys[ $i ] }\n";
}

# delete the element with key 'Joe' from %hash
delete( $hash{ 'Joe' } );

# this loop determines if each key exists, is defined and
# whether the value for the key evaluates to true or false
while ( $key = pop( @hashKeys ) ) {
   print "\n";

   # determine if a particular key exists 
   if ( exists( $hash{ $key } ) ) {
      print "$key exists in the hash.\n";
   }
   else {
      print "$key doesn't exist in the hash.\n";
   }

   # determine if the value for the key is defined
   if ( defined( $hash{ $key } ) ) {
      print "$key is defined as $hash{ $key }.\n";
   }
   else {
      print "$key is undefined.\n";
   }

   # determine if the value for the key is true or false
   if ( $hash{ $key } ) {
      print "$key is true.\n";
   }
   else {
      print "$key is false.\n";
   }
}


###########################################################################
#  (C) Copyright 2001 by Deitel & Associates, Inc. and Prentice Hall.     #
#  All Rights Reserved.                                                   #
#                                                                         #
#  DISCLAIMER: The authors and publisher of this book have used their     #
#  best efforts in preparing the book. These efforts include the          #
#  development, research, and testing of the theories and programs        #
#  to determine their effectiveness. The authors and publisher make       #
#  no warranty of any kind, expressed or implied, with regard to these    #
#  programs or to the documentation contained in these books. The authors #
#  and publisher shall not be liable in any event for incidental or       #
#  consequential damages in connection with, or arising out of, the       #
#  furnishing, performance, or use of these programs.                     #
###########################################################################