这几天，我在学习PHP语言中的SPL。

这个东西应该属于PHP中的高级内容，看上去非常复杂，可是非常实用，所以我做了长篇笔记。不然记不住，以后要用的时候，还是要从头学起。

因为这是供自己參考的笔记，不是教程，所以写得比較简单，没有多解释。可是我想，假设你是一个熟练的PHP5程序猿，应该足以看懂以下的材料，并且会发现它非常实用。如今除此之外，网上根本没有不论什么深入的SPL中文介绍。

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PHP SPL笔记

文件夹

第一部分 简单介绍

1. 什么是SPL？

2. 什么是Iterator？

第二部分 SPL Interfaces

3. Iterator界面

4. ArrayAccess界面

5. IteratorAggregate界面

6. RecursiveIterator界面

7. SeekableIterator界面

8. Countable界面

第三部分 SPL Classes

9. SPL的内置类

10. DirectoryIterator类

11. ArrayObject类

12. ArrayIterator类

13. RecursiveArrayIterator类和RecursiveIteratorIterator类

14. FilterIterator类

15. SimpleXMLIterator类

16. CachingIterator类

17. LimitIterator类

18. SplFileObject类

第一部 简单介绍

1. 什么是SPL？

SPL是Standard PHP Library（PHP标准库）的缩写。

依据官方定义，它是"a collection of interfaces and classes that are meant to solve standard problems"。可是，眼下在使用中，SPL很多其它地被看作是一种使object（物体）模仿array（数组）行为的interfaces和classes。

2. 什么是Iterator？

SPL的核心概念就是Iterator。这指的是一种Design Pattern，依据《Design Patterns》一书的定义，Iterator的作用是"provide an object which traverses some aggregate structure, abstracting away assumptions about the implementation of that structure."

wikipedia中说，"an iterator is an object which allows a programmer to traverse through all the elements of a collection, regardless of its specific implementation"......."the iterator pattern is a design pattern in which iterators are used to access the elements of an aggregate object sequentially without exposing its underlying representation".

通俗地说，Iterator可以使很多不同的数据结构，都能有统一的操作界面，比方一个数据库的结果集、同一个文件夹中的文件集、或者一个文本中每一行构成的集合。

假设依照一般情况，遍历一个MySQL的结果集，程序须要这样写：

// Fetch the "aggregate structure"
$result = mysql_query("SELECT * FROM users");// Iterate over the structure
while ( $row = mysql_fetch_array($result) ) {// do stuff with the row here
}

读出一个文件夹中的内容，须要这样写：

// Fetch the "aggregate structure"
$dh = opendir('/home/harryf/files');// Iterate over the structure
while ( $file = readdir($dh) ) {// do stuff with the file here
}

读出一个文本文件的内容，须要这样写：

// Fetch the "aggregate structure"
$fh = fopen("/home/hfuecks/files/results.txt", "r");// Iterate over the structure
while (!feof($fh)) {$line = fgets($fh);// do stuff with the line here}

上面三段代码，尽管处理的是不同的resource（资源），可是功能都是遍历结果集（loop over contents），因此Iterator的基本思想，就是将这三种不同的操作统一起来，用相同的命令界面，处理不同的资源。

第二部分 SPL Interfaces

3. Iterator界面

SPL规定，全部部署了Iterator界面的class，都能够用在foreach Loop中。Iterator界面中包括5个必须部署的方法：

    * current()This method returns the current index's value. You are solelyresponsible for tracking what the current index is as the interface does not do this for you.* key()This method returns the value of the current index's key. For foreach loops this is extremely important so that the key value can be populated.* next()This method moves the internal index forward one entry.* rewind()This method should reset the internal index to the first element.* valid()This method should return true or false if there is a current element. It is called after rewind() or next().

以下就是一个部署了Iterator界面的class演示样例：

/**
* An iterator for native PHP arrays, re-inventing the wheel
*
* Notice the "implements Iterator" - important!
*/
class ArrayReloaded implements Iterator {/*** A native PHP array to iterate over*/private $array = array();/*** A switch to keep track of the end of the array*/private $valid = FALSE;/*** Constructor* @param array native PHP array to iterate over*/function __construct($array) {$this->array = $array;}/*** Return the array "pointer" to the first element* PHP's reset() returns false if the array has no elements*/function rewind(){$this->valid = (FALSE !== reset($this->array));}/*** Return the current array element*/function current(){return current($this->array);}/*** Return the key of the current array element*/function key(){return key($this->array);}/*** Move forward by one* PHP's next() returns false if there are no more elements*/function next(){$this->valid = (FALSE !== next($this->array));}/*** Is the current element valid?*/function valid(){return $this->valid;}
}

用法例如以下：

// Create iterator object
$colors = new ArrayReloaded(array ('red','green','blue',));// Iterate away!
foreach ( $colors as $color ) {echo $color."<br>";
}

你也能够在foreach循环中使用key()方法：

// Display the keys as well
foreach ( $colors as $key => $color ) {echo "$key: $color<br>";
}

除了foreach循环外，也能够使用while循环，

// Reset the iterator - foreach does this automatically
$colors->rewind();// Loop while valid
while ( $colors->valid() ) {echo $colors->key().": ".$colors->current()."
";$colors->next();}

依据測试，while循环要稍快于foreach循环，由于执行时少了一层中间调用。

4. ArrayAccess界面

部署ArrayAccess界面，能够使得object像array那样操作。ArrayAccess界面包括四个必须部署的方法：

    * offsetExists($offset)This method is used to tell php if there is a valuefor the key specified by offset. It should return true or false.* offsetGet($offset)This method is used to return the value specified by the key offset.* offsetSet($offset, $value)This method is used to set a value within the object, you can throw an exception from this function for a read-only collection.* offsetUnset($offset)This method is used when a value is removed from an array either through unset() or assigning the key a value of null. In the case of numerical arrays, this offset should not be deleted and the array should not be reindexed unless that is specifically the behavior you want.

以下就是一个部署ArrayAccess界面的实例：

/**
* A class that can be used like an array
*/
class Article implements ArrayAccess {public $title;public $author;public $category;  function __construct($title,$author,$category) {$this->title = $title;$this->author = $author;$this->category = $category;}/*** Defined by ArrayAccess interface* Set a value given it's key e.g. $A['title'] = 'foo';* @param mixed key (string or integer)* @param mixed value* @return void*/function offsetSet($key, $value) {if ( array_key_exists($key,get_object_vars($this)) ) {$this->{$key} = $value;}}/*** Defined by ArrayAccess interface* Return a value given it's key e.g. echo $A['title'];* @param mixed key (string or integer)* @return mixed value*/function offsetGet($key) {if ( array_key_exists($key,get_object_vars($this)) ) {return $this->{$key};}}/*** Defined by ArrayAccess interface* Unset a value by it's key e.g. unset($A['title']);* @param mixed key (string or integer)* @return void*/function offsetUnset($key) {if ( array_key_exists($key,get_object_vars($this)) ) {unset($this->{$key});}}/*** Defined by ArrayAccess interface* Check value exists, given it's key e.g. isset($A['title'])* @param mixed key (string or integer)* @return boolean*/function offsetExists($offset) {return array_key_exists($offset,get_object_vars($this));}}

用法例如以下：

// Create the object
$A = new Article('SPL Rocks','Joe Bloggs', 'PHP');// Check what it looks like
echo 'Initial State:<div>';
print_r($A);
echo '</div>';// Change the title using array syntax
$A['title'] = 'SPL _really_ rocks';// Try setting a non existent property (ignored)
$A['not found'] = 1;// Unset the author field
unset($A['author']);// Check what it looks like again
echo 'Final State:<div>';
print_r($A);
echo '</div>';

执行结果例如以下：

Initial State:Article Object
([title] => SPL Rocks[author] => Joe Bloggs[category] => PHP
)Final State:Article Object
([title] => SPL _really_ rocks[category] => PHP
)

能够看到，$A尽管是一个object，可是全然能够像array那样操作。

你还能够在读取数据时，添加程序内部的逻辑：

function offsetGet($key) {if ( array_key_exists($key,get_object_vars($this)) ) {return strtolower($this->{$key});}}

5. IteratorAggregate界面

可是，尽管$A能够像数组那样操作，却无法使用foreach遍历，除非部署了前面提到的Iterator界面。

还有一个解决方法是，有时会须要将数据和遍历部分分开，这时就能够部署IteratorAggregate界面。它规定了一个getIterator()方法，返回一个使用Iterator界面的object。

还是以上一节的Article类为例：

class Article implements ArrayAccess, IteratorAggregate {/*** Defined by IteratorAggregate interface* Returns an iterator for for this object, for use with foreach* @return ArrayIterator*/function getIterator() {return new ArrayIterator($this);}

用法例如以下：

$A = new Article('SPL Rocks','Joe Bloggs', 'PHP');// Loop (getIterator will be called automatically)
echo 'Looping with foreach:<div>';
foreach ( $A as $field => $value ) {echo "$field : $value<br>";
}
echo '</div>';// Get the size of the iterator (see how many properties are left)
echo "Object has ".sizeof($A->getIterator())." elements";

显示结果例如以下：

Looping with foreach:title : SPL Rocks
author : Joe Bloggs
category : PHPObject has 3 elements

6. RecursiveIterator界面

这个界面用于遍历多层数据，它继承了Iterator界面，因而也具有标准的current()、key()、next()、 rewind()和valid()方法。同一时候，它自己还规定了getChildren()和hasChildren()方法。The getChildren() method must return an object that implements RecursiveIterator.

7. SeekableIterator界面

SeekableIterator界面也是Iterator界面的延伸，除了Iterator的5个方法以外，还规定了seek()方法，參数是元素的位置，返回该元素。假设该位置不存在，则抛出OutOfBoundsException。

以下是一个是实例：

<?phpclass PartyMemberIterator implements SeekableIterator
{public function __construct(PartyMember $member){// Store $member locally for iteration}public function seek($index){$this->rewind();$position = 0;while ($position < $index && $this->valid()) {$this->next();$position++;}if (!$this->valid()) {throw new OutOfBoundsException('Invalid position');}}// Implement current(), key(), next(), rewind()// and valid() to iterate over data in $member
}?>

8. Countable界面

这个界面规定了一个count()方法，返回结果集的数量。

第三部分 SPL Classes

9. SPL的内置类

SPL除了定义一系列Interfaces以外，还提供一系列的内置类，它们相应不同的任务，大大简化了编程。

查看全部的内置类，能够使用以下的代码：

<?php
// a simple foreach() to traverse the SPL class names
foreach(spl_classes() as $key=>$value){echo $key.' -&gt; '.$value.'<br />';}
?>

10. DirectoryIterator类

这个类用来查看一个文件夹中的全部文件和子文件夹：

<?phptry{/*** class create new DirectoryIterator Object ***/foreach ( new DirectoryIterator('./') as $Item ){echo $Item.'<br />';}}
/*** if an exception is thrown, catch it here ***/
catch(Exception $e){echo 'No files Found!<br />';
}
?>

查看文件的具体信息：

<table>
<?phpforeach(new DirectoryIterator('./' ) as $file ){if( $file->getFilename()  == 'foo.txt' ){echo '<tr><td>getFilename()</td><td> '; var_dump($file->getFilename()); echo '</td></tr>';echo '<tr><td>getBasename()</td><td> '; var_dump($file->getBasename()); echo '</td></tr>';echo '<tr><td>isDot()</td><td> '; var_dump($file->isDot()); echo '</td></tr>';echo '<tr><td>__toString()</td><td> '; var_dump($file->__toString()); echo '</td></tr>';echo '<tr><td>getPath()</td><td> '; var_dump($file->getPath()); echo '</td></tr>';echo '<tr><td>getPathname()</td><td> '; var_dump($file->getPathname()); echo '</td></tr>';echo '<tr><td>getPerms()</td><td> '; var_dump($file->getPerms()); echo '</td></tr>';echo '<tr><td>getInode()</td><td> '; var_dump($file->getInode()); echo '</td></tr>';echo '<tr><td>getSize()</td><td> '; var_dump($file->getSize()); echo '</td></tr>';echo '<tr><td>getOwner()</td><td> '; var_dump($file->getOwner()); echo '</td></tr>';echo '<tr><td>$file->getGroup()</td><td> '; var_dump($file->getGroup()); echo '</td></tr>';echo '<tr><td>getATime()</td><td> '; var_dump($file->getATime()); echo '</td></tr>';echo '<tr><td>getMTime()</td><td> '; var_dump($file->getMTime()); echo '</td></tr>';echo '<tr><td>getCTime()</td><td> '; var_dump($file->getCTime()); echo '</td></tr>';echo '<tr><td>getType()</td><td> '; var_dump($file->getType()); echo '</td></tr>';echo '<tr><td>isWritable()</td><td> '; var_dump($file->isWritable()); echo '</td></tr>';echo '<tr><td>isReadable()</td><td> '; var_dump($file->isReadable()); echo '</td></tr>';echo '<tr><td>isExecutable(</td><td> '; var_dump($file->isExecutable()); echo '</td></tr>';echo '<tr><td>isFile()</td><td> '; var_dump($file->isFile()); echo '</td></tr>';echo '<tr><td>isDir()</td><td> '; var_dump($file->isDir()); echo '</td></tr>';echo '<tr><td>isLink()</td><td> '; var_dump($file->isLink()); echo '</td></tr>';echo '<tr><td>getFileInfo()</td><td> '; var_dump($file->getFileInfo()); echo '</td></tr>';echo '<tr><td>getPathInfo()</td><td> '; var_dump($file->getPathInfo()); echo '</td></tr>';echo '<tr><td>openFile()</td><td> '; var_dump($file->openFile()); echo '</td></tr>';echo '<tr><td>setFileClass()</td><td> '; var_dump($file->setFileClass()); echo '</td></tr>';echo '<tr><td>setInfoClass()</td><td> '; var_dump($file->setInfoClass()); echo '</td></tr>';}
}
?>
</table>

除了foreach循环外，还能够使用while循环：

<?php
/*** create a new iterator object ***/
$it = new DirectoryIterator('./');/*** loop directly over the object ***/
while($it->valid()){echo $it->key().' -- '.$it->current().'<br />';/*** move to the next iteration ***/$it->next();}
?>

假设要过滤全部子文件夹，能够在valid()方法中过滤：

<?php
/*** create a new iterator object ***/
$it = new DirectoryIterator('./');/*** loop directly over the object ***/
while($it->valid()){/*** check if value is a directory ***/if($it->isDir()){/*** echo the key and current value ***/echo $it->key().' -- '.$it->current().'<br />';}/*** move to the next iteration ***/$it->next();}
?>

11. ArrayObject类

这个类能够将Array转化为object。

<?php/*** a simple array ***/
$array = array('koala', 'kangaroo', 'wombat', 'wallaby', 'emu', 'kiwi', 'kookaburra', 'platypus');/*** create the array object ***/
$arrayObj = new ArrayObject($array);/*** iterate over the array ***/
for($iterator = $arrayObj->getIterator();/*** check if valid ***/$iterator->valid();/*** move to the next array member ***/$iterator->next()){/*** output the key and current array value ***/echo $iterator->key() . ' => ' . $iterator->current() . '<br />';}
?>

添加一个元素：

$arrayObj->append('dingo');

对元素排序：

$arrayObj->natcasesort();

显示元素的数量：

echo $arrayObj->count();

删除一个元素：

$arrayObj->offsetUnset(5);

某一个元素是否存在：

 if ($arrayObj->offsetExists(3)){echo 'Offset Exists<br />';}

更改某个位置的元素值：

 $arrayObj->offsetSet(5, "galah");

显示某个位置的元素值：

echo $arrayObj->offsetGet(4);

12. ArrayIterator类

这个类实际上是对ArrayObject类的补充，为后者提供遍历功能。

示比例如以下：

<?php
/*** a simple array ***/
$array = array('koala', 'kangaroo', 'wombat', 'wallaby', 'emu', 'kiwi', 'kookaburra', 'platypus');try {$object = new ArrayIterator($array);foreach($object as $key=>$value){echo $key.' => '.$value.'<br />';}}
catch (Exception $e){echo $e->getMessage();}
?>

ArrayIterator类也支持offset类方法和count()方法：

<ul>
<?php
/*** a simple array ***/
$array = array('koala', 'kangaroo', 'wombat', 'wallaby', 'emu', 'kiwi', 'kookaburra', 'platypus');try {$object = new ArrayIterator($array);/*** check for the existence of the offset 2 ***/if($object->offSetExists(2)){/*** set the offset of 2 to a new value ***/$object->offSetSet(2, 'Goanna');}/*** unset the kiwi ***/foreach($object as $key=>$value){/*** check the value of the key ***/if($object->offSetGet($key) === 'kiwi'){/*** unset the current key ***/$object->offSetUnset($key);}echo '<li>'.$key.' - '.$value.'</li>'."\n";}}
catch (Exception $e){echo $e->getMessage();}
?>
</ul>

13. RecursiveArrayIterator类和RecursiveIteratorIterator类

ArrayIterator类和ArrayObject类，仅仅支持遍历一维数组。假设要遍历多维数组，必须先用RecursiveIteratorIterator生成一个Iterator，然后再对这个Iterator使用RecursiveIteratorIterator。

<?php
$array = array(array('name'=>'butch', 'sex'=>'m', 'breed'=>'boxer'),array('name'=>'fido', 'sex'=>'m', 'breed'=>'doberman'),array('name'=>'girly','sex'=>'f', 'breed'=>'poodle')
);foreach(new RecursiveIteratorIterator(new RecursiveArrayIterator($array)) as $key=>$value){echo $key.' -- '.$value.'<br />';}
?>

14. FilterIterator类

FilterIterator类能够对元素进行过滤，仅仅要在accept()方法中设置过滤条件就能够了。

示比例如以下：

<?php
/*** a simple array ***/
$animals = array('koala', 'kangaroo', 'wombat', 'wallaby', 'emu', 'NZ'=>'kiwi', 'kookaburra', 'platypus');class CullingIterator extends FilterIterator{/*** The filteriterator takes  a iterator as param: ***/
public function __construct( Iterator $it ){parent::__construct( $it );
}/*** check if key is numeric ***/
function accept(){return is_numeric($this->key());
}}/*** end of class ***/
$cull = new CullingIterator(new ArrayIterator($animals));foreach($cull as $key=>$value){echo $key.' == '.$value.'<br />';}
?>

以下是还有一个返回质数的样例：

<?phpclass PrimeFilter extends FilterIterator{/*** The filteriterator takes  a iterator as param: ***/
public function __construct(Iterator $it){parent::__construct($it);
}/*** check if current value is prime ***/
function accept(){
if($this->current() % 2 != 1){return false;}
$d = 3;
$x = sqrt($this->current());
while ($this->current() % $d != 0 && $d < $x){$d += 2;}return (($this->current() % $d == 0 && $this->current() != $d) * 1) == 0 ? true : false;
}}/*** end of class ***//*** an array of numbers ***/
$numbers = range(212345,212456);/*** create a new FilterIterator object ***/
$primes = new primeFilter(new ArrayIterator($numbers));foreach($primes as $value){echo $value.' is prime.<br />';}
?>

15. SimpleXMLIterator类

这个类用来遍历xml文件。

示比例如以下：

<?php/*** a simple xml tree ***/$xmlstring = <<<XML
<?xml version = "1.0" encoding="UTF-8" standalone="yes"?>
<document><animal><category id="26"><species>Phascolarctidae</species><type>koala</type><name>Bruce</name></category></animal><animal><category id="27"><species>macropod</species><type>kangaroo</type><name>Bruce</name></category></animal><animal><category id="28"><species>diprotodon</species><type>wombat</type><name>Bruce</name></category></animal><animal><category id="31"><species>macropod</species><type>wallaby</type><name>Bruce</name></category></animal><animal><category id="21"><species>dromaius</species><type>emu</type><name>Bruce</name></category></animal><animal><category id="22"><species>Apteryx</species><type>kiwi</type><name>Troy</name></category></animal><animal><category id="23"><species>kingfisher</species><type>kookaburra</type><name>Bruce</name></category></animal><animal><category id="48"><species>monotremes</species><type>platypus</type><name>Bruce</name></category></animal><animal><category id="4"><species>arachnid</species><type>funnel web</type><name>Bruce</name><legs>8</legs></category></animal>
</document>
XML;/*** a new simpleXML iterator object ***/
try    {/*** a new simple xml iterator ***/$it = new SimpleXMLIterator($xmlstring);/*** a new limitIterator object ***/foreach(new RecursiveIteratorIterator($it,1) as $name => $data){echo $name.' -- '.$data.'<br />';}}
catch(Exception $e){echo $e->getMessage();}
?>

new RecursiveIteratorIterator($it,1)表示显示全部包含父元素在内的子元素。

显示某一个特定的元素值，能够这样写：

<?php
try {/*** a new simpleXML iterator object ***/$sxi =  new SimpleXMLIterator($xmlstring);foreach ( $sxi as $node ){foreach($node as $k=>$v){echo $v->species.'<br />';}}}
catch(Exception $e){echo $e->getMessage();}
?>

相相应的while循环写法为：

<?phptry {
$sxe = simplexml_load_string($xmlstring, 'SimpleXMLIterator');for ($sxe->rewind(); $sxe->valid(); $sxe->next()){if($sxe->hasChildren()){foreach($sxe->getChildren() as $element=>$value){echo $value->species.'<br />';}}}}
catch(Exception $e){echo $e->getMessage();}
?>

最方便的写法，还是使用xpath：

<?php
try {/*** a new simpleXML iterator object ***/$sxi =  new SimpleXMLIterator($xmlstring);/*** set the xpath ***/$foo = $sxi->xpath('animal/category/species');/*** iterate over the xpath ***/foreach ($foo as $k=>$v){echo $v.'<br />';}}
catch(Exception $e){echo $e->getMessage();}
?>

以下的样例，显示有namespace的情况：

<?php/*** a simple xml tree ***/$xmlstring = <<<XML
<?xml version = "1.0" encoding="UTF-8" standalone="yes"?>
<document xmlns:spec="http://example.org/animal-species"><animal><category id="26"><species>Phascolarctidae</species><spec:name>Speed Hump</spec:name><type>koala</type><name>Bruce</name></category></animal><animal><category id="27"><species>macropod</species><spec:name>Boonga</spec:name><type>kangaroo</type><name>Bruce</name></category></animal><animal><category id="28"><species>diprotodon</species><spec:name>pot holer</spec:name><type>wombat</type><name>Bruce</name></category></animal><animal><category id="31"><species>macropod</species><spec:name>Target</spec:name><type>wallaby</type><name>Bruce</name></category></animal><animal><category id="21"><species>dromaius</species><spec:name>Road Runner</spec:name><type>emu</type><name>Bruce</name></category></animal><animal><category id="22"><species>Apteryx</species><spec:name>Football</spec:name><type>kiwi</type><name>Troy</name></category></animal><animal><category id="23"><species>kingfisher</species><spec:name>snaker</spec:name><type>kookaburra</type><name>Bruce</name></category></animal><animal><category id="48"><species>monotremes</species><spec:name>Swamp Rat</spec:name><type>platypus</type><name>Bruce</name></category></animal><animal><category id="4"><species>arachnid</species><spec:name>Killer</spec:name><type>funnel web</type><name>Bruce</name><legs>8</legs></category></animal>
</document>
XML;/*** a new simpleXML iterator object ***/
try {/*** a new simpleXML iterator object ***/$sxi =  new SimpleXMLIterator($xmlstring);$sxi-> registerXPathNamespace('spec', 'http://www.exampe.org/species-title');/*** set the xpath ***/$result = $sxi->xpath('//spec:name');/*** get all declared namespaces ***/foreach($sxi->getDocNamespaces('animal') as $ns){echo $ns.'<br />';}/*** iterate over the xpath ***/foreach ($result as $k=>$v){echo $v.'<br />';}}
catch(Exception $e){echo $e->getMessage();}
?>

添加一个节点：

<?php $xmlstring = <<<XML
<?xml version = "1.0" encoding="UTF-8" standalone="yes"?>
<document><animal>koala</animal><animal>kangaroo</animal><animal>wombat</animal><animal>wallaby</animal><animal>emu</animal><animal>kiwi</animal><animal>kookaburra</animal><animal>platypus</animal><animal>funnel web</animal>
</document>
XML;try {/*** a new simpleXML iterator object ***/$sxi =  new SimpleXMLIterator($xmlstring);/*** add a child ***/$sxi->addChild('animal', 'Tiger');/*** a new simpleXML iterator object ***/$new = new SimpleXmlIterator($sxi->saveXML());/*** iterate over the new tree ***/foreach($new as $val){echo $val.'<br />';}}
catch(Exception $e){echo $e->getMessage();}
?>

添加属性：

<?php
$xmlstring =<<<XML
<?xml version = "1.0" encoding="UTF-8" standalone="yes"?>
<document><animal>koala</animal><animal>kangaroo</animal><animal>wombat</animal><animal>wallaby</animal><animal>emu</animal><animal>kiwi</animal><animal>kookaburra</animal><animal>platypus</animal><animal>funnel web</animal>
</document>
XML;try {/*** a new simpleXML iterator object ***/$sxi =  new SimpleXMLIterator($xmlstring);/*** add an attribute with a namespace ***/$sxi->addAttribute('id:att1', 'good things', 'urn::test-foo');/*** add an attribute without a  namespace ***/$sxi->addAttribute('att2', 'no-ns');echo htmlentities($sxi->saveXML());}
catch(Exception $e){echo $e->getMessage();}
?>

16. CachingIterator类

这个类有一个hasNext()方法，用来推断是否还有下一个元素。

示比例如以下：

<?php
/*** a simple array ***/
$array = array('koala', 'kangaroo', 'wombat', 'wallaby', 'emu', 'kiwi', 'kookaburra', 'platypus');try {/*** create a new object ***/$object = new CachingIterator(new ArrayIterator($array));foreach($object as $value){echo $value;if($object->hasNext()){echo ',';}}}
catch (Exception $e){echo $e->getMessage();}
?>

17. LimitIterator类

这个类用来限定返回结果集的数量和位置，必须提供offset和limit两个參数，与SQL命令中limit语句类似。

示比例如以下：

<?php
/*** the offset value ***/
$offset = 3;/*** the limit of records to show ***/
$limit = 2;$array = array('koala', 'kangaroo', 'wombat', 'wallaby', 'emu', 'kiwi', 'kookaburra', 'platypus');$it = new LimitIterator(new ArrayIterator($array), $offset, $limit);foreach($it as $k=>$v){echo $it->getPosition().'<br />';}
?>

还有一个样例是：

<?php/*** a simple array ***/
$array = array('koala', 'kangaroo', 'wombat', 'wallaby', 'emu', 'kiwi', 'kookaburra', 'platypus');$it = new LimitIterator(new ArrayIterator($array));try{$it->seek(5);echo $it->current();}
catch(OutOfBoundsException $e){echo $e->getMessage() . "<br />";}
?>

18. SplFileObject类

这个类用来对文本文件进行遍历。

示比例如以下：

<?phptry{// iterate directly over the objectforeach( new SplFileObject(&quot;/usr/local/apache/logs/access_log&quot;) as $line)// and echo each line of the fileecho $line.'<br />';
}
catch (Exception $e){echo $e->getMessage();}
?>

返回文本文件的第三行，能够这样写：

<?phptry{$file = new SplFileObject("/usr/local/apache/logs/access_log");$file->seek(3);echo $file->current();}
catch (Exception $e){echo $e->getMessage();}
?>

[參考文献]

1. Introduction to Standard PHP Library (SPL), By Kevin Waterson

2. Introducing PHP 5's Standard Library, By Harry Fuecks

3. The Standard PHP Library (SPL), By Ben Ramsey

4. SPL - Standard PHP Library Documentation

（完）