Perl Quote

Author：Eve Cole Update Time：2024-12-26 11:12:01

A reference is a pointer. A Perl reference is a scalar type that can point to a variable, array, hash table (also called an associative array) or even a subroutine, and can be applied anywhere in the program.

Create reference

When defining a variable, add in front of the variable name to get a reference to the variable, for example:

 $scalarref = $foo; # Scalar variable reference $arrayref = @ARGV; # List reference $hashref = %ENV; # Hash reference $coderef = &handler; # Subroutine reference $globref = *foo ; # GLOB handle reference

We can use anonymous array references in arrays, using [] definition:

 $aref= [ 1,"foo",undef,13 ];

The elements of an anonymous array can still be an anonymous array, so we can use this method to construct an array of arrays, and we can construct an array of any dimension.

 my $aref = [ [1, 2, 3], [4, 5, 6], [7, 8, 9],]

In hashes we can use anonymous hash references, defined using {}:

 $href= { APR =>4, AUG =>8 };

We can also create an anonymous subroutine reference without a subroutine name:

 $coderef = sub { print "Codercto!n" };

dereference

Dereference can be canceled using $, @ or % according to different types. Examples are as follows:

Example

#!/usr/bin/perl $var = 10 ; # $r refers to the $var scalar $r = $var ; # Output the variable value of $r stored locally print " $var is: " , $ $r , " n " ; @var = ( 1 , 2 , 3 ) ; # $r refers to the @var array $r = @var ; # Output the variable value of $r stored locally print " @var is: " , @ $r , " n " ; %var = ( ' key1 ' => 10 , ' key2 ' => 20 ) ; # $r refers to the %var array $r = %var ; # Output the variable value of $r stored locally print " %var is: " , % $r , " n " ;

The result of executing the above example is:

 10 is: 101 2 3 is: 123%var is: key110key220

If you are not sure of the variable type, you can use ref to determine it. The return value list is as follows. If there is no following value, it returns false:

 SCALARARRAYHASHCODEGLOBREF

Examples are as follows:

Example

#!/usr/bin/perl $var = 10 ; $r = $var ; print " Reference type of r: " , ref ( $r ) , " n " ; @var = ( 1 , 2 , 3 ) ; $r = @var ; print " Reference type of r: " , ref ( $r ) , " n " ; %var = ( ' key1 ' => 10 , ' key2 ' => 20 ) ; $r = %var ; print " Reference type of r: " , ref ( $r ) , " n " ;

The result of executing the above example is:

 Reference type of r: SCALAR Reference type of r: ARRAYr Reference type: HASH

circular reference

A circular reference occurs when two references contain each other. You need to use it carefully, otherwise it will cause memory leaks, as in the following example:

Example

#!/usr/bin/perl my $foo = 100 ; $foo = $foo ; print " Value of foo is : " , $ $foo , " n " ;

The result of executing the above example is:

 Value of foo is : REF(0x9aae38)

reference function

Function reference format: &

The format of calling the reference function: & + the created reference name.

Examples are as follows:

Example

#!/usr/bin/perl # Function definition sub PrintHash { my ( %hash ) = @_ ; foreach $item ( %hash ) { print " Element: $item n " ; } } %hash = ( ' name ' => ' codercto ' , ' age ' => 3 ) ; # Create a reference to the function $cref = & PrintHash ; # Call function using reference & $cref ( %hash ) ;

The result of executing the above example is:

 element: age element: 3 element: name element: codercto