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。

perl

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

perl

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

perl

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};

perl constant的使用

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