The best Perl references Tutorial In 2024, In this tutorial you can learn Create references,Dereference,Circular references,Reference Functions,
Reference is a pointer, Perl reference is a scalar type can point to variables, arrays, hash tables (also called associative arrays) or subroutine can be used anywhere in the program.
Defined variables, the variable name preceded by a \, we get a reference to the variable, such as:
$scalarref = \$foo; # 标量变量引用 $arrayref = \@ARGV; # 列表的引用 $hashref = \%ENV; # 哈希的引用 $coderef = \&handler; # 子过程引用 $globref = \*foo; # GLOB句柄引用
In the array, we can use an anonymous array reference, use [] Definition:
$aref= [ 1,"foo",undef,13 ];
Anonymous array elements can still be anonymous array, so we can use this method to construct an array of arrays, the array may be constructed of any dimension.
my $aref = [ [1, 2, 3], [4, 5, 6], [7, 8, 9], ]
We can use a hash anonymous hash references, use {} definition:
$href= { APR =>4, AUG =>8 };
We can not create a subroutine name anonymous subroutine reference:
$coderef = sub { print "w3big!\n" };
Cancel application can be used depending on the type of $, @ or%, to cancel, examples are as follows:
#!/usr/bin/perl $var = 10; # $r 引用 $var 标量 $r = \$var; # 输出本地存储的 $r 的变量值 print "$var 为 : ", $$r, "\n"; @var = (1, 2, 3); # $r 引用 @var 数组 $r = \@var; # 输出本地存储的 $r 的变量值 print "@var 为: ", @$r, "\n"; %var = ('key1' => 10, 'key2' => 20); # $r 引用 %var 数组 $r = \%var; # 输出本地存储的 $r 的变量值 print "%var 为 : ", %$r, "\n";
Implementation of the above example the result is:
10 为 : 10 1 2 3 为: 123 %var 为 : key110key220
If you can not determine the variable type, you can use theref to determine the return value listed below, the following value is returned if there is no false:
SCALAR ARRAY HASH CODE GLOB REF
Examples are as follows:
#!/usr/bin/perl $var = 10; $r = \$var; print "r 的引用类型 : ", ref($r), "\n"; @var = (1, 2, 3); $r = \@var; print "r 的引用类型 : ", ref($r), "\n"; %var = ('key1' => 10, 'key2' => 20); $r = \%var; print "r 的引用类型 : ", ref($r), "\n";
Implementation of the above example the result is:
r 的引用类型 : SCALAR r 的引用类型 : ARRAY r 的引用类型 : HASH
Circular references cited in two mutually inclusive emergence. You need to be careful to use, otherwise it will lead to memory leaks, the following examples:
#!/usr/bin/perl my $foo = 100; $foo = \$foo; print "Value of foo is : ", $$foo, "\n";
Implementation of the above example the result is:
Value of foo is : REF(0x9aae38)
Function Reference format: \ &
Reference function call format: & + reference name created.
Examples are as follows:
#!/usr/bin/perl # 函数定义 sub PrintHash{ my (%hash) = @_; foreach $item (%hash){ print "元素 : $item\n"; } } %hash = ('name' => 'w3big', 'age' => 3); # 创建函数的引用 $cref = \&PrintHash; # 使用引用调用函数 &$cref(%hash);
Implementation of the above example the result is:
元素 : age 元素 : 3 元素 : name 元素 : w3big