\$b-\$a - Using Hard References in Other Operations

Perl Tutorials - Herong's Tutorial Examples

Dr. Herong Yang, Version 5.10

Perl Tutorials - Herong's Tutorial Examples

∟Hard References - Addresses of Memory Objects

∟\$b-\$a - Using Hard References in Other Operations

This section provides a tutorial example on using hard references as numeric, string or Boolean values in other operations.

A hard reference can also be used as scalar value in other operations:

It will return an integer representing the memory location of the referenced object, if a number is expected. This allows you to calculate the memory location difference by subtracting one reference from another reference.
It will return the object type and memory location in hex of the referenced object, if a string is expected.
It will return TRUE, if a Boolean value is expected.

Here is a tutorial program to help you understand this:

#- HardRef5.pl
#- Copyright (c) 1999 by Dr. Herong Yang, http://www.herongyang.com/
#
   $a = 3;
   $b = 5;
   $x = '1234';
   $y = 'abcd';
   @l = (3,5,7,11);
   print '\$a = ', \$a, "\n";
   print '\$b = ', \$b, "\n";
   print '\$x = ', \$x, "\n";
   print '\$y = ', \$y, "\n";
   print '\@l = ', \@l, "\n";
   print '\$l[0] = ', \$l[0], "\n";
   print '\$l[1] = ', \$l[1], "\n";
   print '\$b - \$a = ', \$b - \$a, "\n";
   print '\$y - \$x = ', \$y - \$x, "\n";
   print '\$l[1] - \$l[0] = ', \$l[1] - \$l[0], "\n";
#   print '${\$a+36} = ', ${\$a+36}, "\n";

Here is the output of this tutorial program:

\$a = SCALAR(0x1ab2e38)
\$b = SCALAR(0x1ab2e5c)
\$x = SCALAR(0x1ab2e80)
\$y = SCALAR(0x1ab2ea4)
\@l = ARRAY(0x1ab2ed4)
\$l[0] = SCALAR(0x1abf074)
\$l[1] = SCALAR(0x1abf128)
\$b - \$a = 36
\$y - \$x = 36
\$l[1] - \$l[0] = 180

The output shows that the address of $b is higher than $a by 36. But trying to use ${\$a+36} to access $b will not work. I have tried already.

Table of Contents

About This Book

Perl on Linux Systems

ActivePerl on Windows Systems

Data Types: Values and Variables

Expressions, Operations and Simple Statements

User Defined Subroutines

Perl Built-in Debugger

Name Spaces and Perl Module Files

Symbolic (or Soft) References

►Hard References - Addresses of Memory Objects