Perl 引用（即指针） 学习笔记

前言

    Perl引用就是指针，可以指向变量、数组、哈希表（也叫关联数组）甚至子程序。Pascal或C程序员应该对引用（即指针）的概念很熟悉，引用就是某值的地址，对其的使用则取决于程序员和语言的规定。在Perl中，可以把引用称为指针，二者是通用的，无差别的。引用在创建复杂数据方面十分有用。
    下面的内容为学习笔记，例子都测试过了，效果不错！

 

一、简单的例子

 

引用变量$pointer存的是$variable的地址，

而不是值本身，要获得值，形式为两个$符号

 

#!/usr/bin/perl -w
my $value = 10;
$pointer = /$value;
printf "/n Pointer Address $pointer of $value /n";
printf "/n What Pointer *($pointer) points to $$pointer/n";

打印结果：

Pointer Address SCALAR(0x182ba3c) of 10
What Pointer *(SCALAR(0x182ba3c)) points to 10

 

二、引用和数组

 

       $pointer 存储的是数组的地址，通过调用 scalar 函数去获得数组的个数

并且通过加 $ 解引用这个地址。

 

 

#!/usr/bin/perl -w
use strict;

my @array_demo = (1,2,3,4);
my $pointer = /@array_demo;
printf "Pointer Address of array_demo = $pointer/n";

#调用函数scalar()获得数组的元素个数
my $i = scalar(@$pointer);
printf "Number of arguments : $i /n";

#print the array all element
#通过引用访问哈希表的元素形式为$$pointer{$index}，
$i = 0;
foreach (@$pointer) {
 printf "$i : $$pointer[$i++]; /n";
}

 

打印结果：

Pointer Address of array_demo = ARRAY(0x182ba84)
Number of arguments : 4
0 : 1;
1 : 2;
2 : 3;
3 : 4;

 

三、引用与哈希数列

 

       与数组类似，通过引用访问哈希表的元素形式为$$pointer{$index}，当然，$index是哈希表的键值，而不仅是数字。还有几种访问形式，此外，构建哈希表还可以用=>操作符，可读性更好些。下面再看一个例子：

 

#!/usr/bin/perl -w
use strict;

my %month = (
 "01" => 'Jan',
 "02" => 'Feb',
 "03" => 'Mar',
 "04" => 'Apr',
 "05" => 'May',
 "06" => 'Jun',
);

#print the hash address
my $pointer = /%month;
printf "/n Address of hash = $pointer/n ";

# The following lines would be used to print out the
# contents of the associative array if %month was used.
foreach my $i (sort keys %month) {
 printf "$i is $$pointer{$i} /n";
}

print "$$pointer{'02'}","/n";
print "$pointer->{'03'}","/n";

 

 

程序打印结果：

 

Address of hash = HASH(0x182ba1c)
01 is Jan
02 is Feb
03 is Mar
04 is Apr
05 is May
06 is Jun
Feb
Mar

思考一下，这里地址和实际的值使用上有什么区别？

 

print "$$pointer{'02'}","/n";        #这里Pointer 为地址
print "$month{'02'}","/n";           #为实际的数值

print "$pointer->{'02'}","/n";      #这个是比较方便的一种，速度块并且易读的一种写法

 

 

四、多维数组

 

#!/usr/bin/perl -w
use strict;

my $line = ['solid', 'black', ['1','2','3', ['4', '5', '6']]];
print "/$line->[0] = $line->[0] /n";
print "/$line->[1] = $line->[1] /n";
print "/$line->[2][0] = $line->[2][0] /n";
print "/$line->[2][1] = $line->[2][1] /n";
print "/$line->[2][2] = $line->[2][2] /n";
print "/$line->[2][3][0] = $line->[2][3][0] /n";
print "/$line->[2][3][1] = $line->[2][3][1] /n";
print "/$line->[2][3][2] = $line->[2][3][2] /n";

打印结果：

$line->[0] = solid
$line->[1] = black
$line->[2][0] = 1
$line->[2][1] = 2
$line->[2][2] = 3
$line->[2][3][0] = 4
$line->[2][3][1] = 5
$line->[2][3][2] = 6

 

 

五、引用与哈希

 

 

#!/usr/bin/perl -w
use strict;

my %cube = (
'0'=>['0', '0', '0'],
'1'=>['0', '0', '1'],
'2'=>['0', '1', '0'],
'3'=>['0', '1', '1'],
'4'=>['1', '0', '0'],
'5'=>['1', '0', '1'],
'6'=>['1', '1', '0'],
'7'=>['1', '1', '1']
);
my $pointer = /%cube;

foreach my $i (sort keys %$pointer) {

 my $list = $$pointer{$i};
 my $z = $list->[0];
 my $x = $$pointer{$i}->[1];       #指向数组用 [] 指向哈希为｛｝
 my $y = $pointer->{$i}->[2];
 printf " Point $i = $x,$y,$z /n";
}

打印结果：

 Point 0 = 0,0,0
 Point 1 = 0,1,0
 Point 2 = 1,0,0
 Point 3 = 1,1,0
 Point 4 = 0,0,1
 Point 5 = 0,1,1
 Point 6 = 1,0,1
 Point 7 = 1,1,1

 

六、哈希与子函数

#!/usr/bin/perl
sub errorMsg {
  my $lvl = shift;
  #
  # define the subroutine to run when called.
  #
  return sub {
    my $msg = shift; # Define the error type now.
    print "Err Level $lvl:$msg/n"; }; # print later.
  }
$severe = errorMsg("Severe");
$fatal = errorMsg("Fatal");
$annoy = errorMsg("Annoying");

&$severe("Divide by zero");
&$fatal("Did you forget to use a semi-colon?");
&$annoy("Uninitialized variable in use");

七、 数组引用，

 

数组的地址 / 引用 为地址，

地址通过加入 @解引用

 

#!/usr/bin/perl -w
use strict;

my @names =(1,2,3);

print "$#names,@names";
my $address = /@names;
sub listem{
   my ($list) = @_;
   print (@$list[1],"/n");
}

&listem(/@names);