时间：2021-07-01 10:21:17 帮助过：4人阅读
1. 什么是SPL？
SPL是Standard PHP Library（PHP标准库）的缩写。
根据官方定义，它是“a collection of interfaces and classes that are meant to solve standard problems”。但是，目前在使用中，SPL更多地被看作是一种使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，根据《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能够使许多不同的数据结构，都能有统一的操作界面，比如一个数据库的结果集、同一个目录中的文件集、或者一个文本中每一行构成的集合。
如果按照普通情况，遍历一个MySQL的结果集，程序需要这样写：
// 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
}读出一个目录中的内容，需要这样写：
// 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，需要这样写：
// 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，虽然处理的是不同的resource（资源），但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，用同样的命令界面，处理不同的资源。
第二部分 SPL Interfaces
3. Iterator界面
SPL规定，所有部署了Iterator界面的class，都可以用在foreach Loop中。Iterator界面中包含5个必须部署的方法：
* current()
This method returns the current index’s value. You are solely
responsible 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().下面就是一个部署了Iterator界面的class示例：
/**
* 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;
}
}使用方法如下：
// Create iterator object
$colors = new ArrayReloaded(array ('red','green','blue',));
// Iterate away!
foreach ( $colors as $color ) {
echo $color."<br>";
}你也可以在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，也可以使用while循环，
// Reset the iterator - foreach does this automatically
$colors->rewind();
// Loop while valid
while ( $colors->valid() ) {
echo $colors->key().": ".$colors->current()."
";
$colors->next();
}根据测试，while循环要稍快于foreach循环，因为运行时少了一层中间调用。
4. ArrayAccess界面
部署ArrayAccess界面，可以使得object像array那样操作。ArrayAccess界面包含四个必须部署的方法：
* offsetExists($offset)
This method is used to tell php if there is a value
for 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.下面就是一个部署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));
}
}使用方法如下：
// 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($A);
echo '</div>';运行结果如下：
Initial State: Article Object ( [title] => SPL Rocks [author] => Joe Bloggs [category] => PHP ) Final State: Article Object ( [title] => SPL _really_ rocks [category] => PHP )
可以看到，$A虽然是一个object，但是完全可以像array那样操作。
你还可以在读取数据时，增加程序内部的逻辑：
function offsetGet($key) {
if ( array_key_exists($key,get_object_vars($this)) ) {
return strtolower($this->{$key});
}
}5. IteratorAggregate界面
但是，虽然$A可以像数组那样操作，却无法使用foreach遍历，除非部署了前面提到的Iterator界面。
另一个解决方法是，有时会需要将数据和遍历部分分开，这时就可以部署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);
}使用方法如下：
$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";显示结果如下：
Looping with foreach: title : SPL Rocks author : Joe Bloggs category : PHP Object 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。同时，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，参数是元素的位置，返回该元素。如果该位置不存在，则抛出OutOfBoundsException。
下面是一个是实例：
<?php
class 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，它们对应不同的任务，大大简化了编程。
查看所有的内置类，可以使用下面的代码：
<?php
// a simple foreach() to traverse the SPL class names
foreach(spl_classes() as $key=>$value)
{
echo $key.' -> '.$value.'<br />';
}
?>10. DirectoryIterator类
这个类用来查看一个目录中的所有文件和子目录：
<?php
try{
/*** 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 />';
}
?>查看文件的详细信息：
<table>
<?php
foreach(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，还可以使用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();
}
?>如果要过滤所有子目录，可以在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
这个类可以将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 />';
}
?>增加一个元素：
$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。
示例如下：
<?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，只支持遍历一维数组。如果要遍历多维数组，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类可以对元素进行过滤，只要在accept()方法中设置过滤条件就可以了。
示例如下：
<?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 />';
}
?>下面是另一个返回质数的例子：
<?php
class 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。
示例如下：
<?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)表示显示所有包括父元素在内的子元素。
显示某一个特定的元素值，可以这样写：
<?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();
}
?>相对应的while循环写法为：
<?php
try {
$sxe = simplexml_load_string($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();
}
?>下面的例子，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();
}
?>增加一个节点：
<?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();
}
?>增加属性：
<?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，用来判断是否还有下一个元素。
示例如下：
<?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两个参数，与SQL命令中limit语句类似。
示例如下：
<?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 />';
}
?>另一个例子是：
<?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。
示例如下：
<?php
try{
// iterate directly over the object
foreach( new SplFileObject("/usr/local/apache/logs/access_log") as $line)
// and echo each line of the file
echo $line.'<br />';
}
catch (Exception $e)
{
echo $e->getMessage();
}
?>返回文本文件的第三行，可以这样写：
<?php
try{
$file = new SplFileObject("/usr/local/apache/logs/access_log");
$file->seek(3);
echo $file->current();
}
catch (Exception $e)
{
echo $e->getMessage();
}
?>