perl constant的使用

在perl中使用constant编译指示允许使用常量。常量顾名思义就是在整个程序的执行过程中，变量的值不会发生变化。如果在编写程序的时候， 你能够确定哪些变量的值不在发生变化，你可以使用use constant的方法来定义常量。下面就是标量常量，列表常量，hash常量的使用方法。

Scalar constant

use constant COUNT = > 100;
# ------------------------------------

print COUNT ;

List constant

use constant WEEKDAYS = > qw (
       Sunday Monday Tuesday Wednesday Thursday Friday Saturday
        );
 # ------------------------------------------------------------------------
 print "Today is ",(WEEKDAYS ) [ 1 ],".\n";

Hash constant

 

use constant WEEKABBR = > {
          ‘Monday’ = > ‘Mon’,‘Tuesday’ = > ‘Tue’,‘Wednesday’ = >’Wed’,‘Thursday’ = > ‘Thu’,‘Friday’ = >’Fri’ )
    # ------------------------------------------------------------------------
    %abbr = WEEKABBR;
    $day = ‘Wednesday’;
    print “The abbrevaiation for $day is ”,$abbr { $day };