php变量引用与对象引用详解介绍

<?php
function foo(&$var) { }

foo($a); // $a is "created" and assigned to null

$b = array();
foo($b['b']);
var_dump(array_key_exists('b', $b)); // bool(true)

$c = new StdClass;
foo($c->d);
var_dump(property_exists($c, 'd')); // bool(true)
?>

<?
$a="ABC";
$b =&$a;
echo $a;//这里输出:ABC
echo $b;//这里输出:ABC
$b="EFG";
echo $a;//这里$a的值变为EFG 所以输出EFG
echo $b;//这里输出EFG
?>

function test(&$a)
{
$a=$a+100;
}
$b=1;
echo $b;//输出１
test($b); //这里$b传递给函数的其实是$b的变量内容所处的内存地址，通过在函数里改变$a的值　就可以改变$b的值了
echo "<br>";
echo $b;//输出101

function &test()
{
static $b=0;//申明一个静态变量
$b=$b+1;
echo $b;
return $b;
}

$a=test();//这条语句会输出　$b的值　为１
$a=5;
$a=test();//这条语句会输出　$b的值　为2

$a=&test();//这条语句会输出　$b的值　为3
$a=5;
$a=test();//这条语句会输出　$b的值　为6

<?
class a{
var $abc="ABC";
}
$b=new a;
$c=$b;
echo $b->abc;//这里输出ABC
echo $c->abc;//这里输出ABC
$b->abc="DEF";
echo $c->abc;//这里输出DEF
?>

<?php
$a = 1;
$b =& $a;
unset ($a);
?>

<?php
$var1 = "Example variable";
$var2 = "";

function global_references($use_globals)
{
    global $var1, $var2;
    if (!$use_globals) {
        $var2 =& $var1; // visible only inside the function
    } else {
        $GLOBALS["var2"] =& $var1; // visible also in global context
    }
}

global_references(false);
echo "var2 is set to '$var2'n"; // var2 is set to ''
global_references(true);
echo "var2 is set to '$var2'n"; // var2 is set to 'Example variable'
?>

abstract class Operation{
    abstract public  function getValue($num1,$num2);
    public  function getAttr(){
        return 1;
    }
}
class Add extends Operation{
    public function getValue($num1, $num2){       
        return $num1+$num2;
    }
}

class Sub extends Operation{
    public function getValue($num1, $num2){
        return $num1-$num2;
    }
}

class Factory{
    public static function CreateObj($operation){
       
        switch ($operation){
            case '+': return new Add();
            case '-': return new Sub();
        }
       
    }
}

$Op=Factory::CreateObj('-');
echo $Op->getValue(3, 6);

<?php
interface IUser
{
  function getName();
}

class User implements IUser
{
  public static function Load( $id )
  {
        return new User( $id );
  }

  public static function Create( )
  {
        return new User( null );
  }

  public function __construct( $id ) { }

  public function getName()
  {
    return "Jack";
  }
}

$uo = User::Load( 1 );
echo( $uo->getName()."n" );
?>

index.php

<?php
include_once("f.inc.php");
$f=new factory;
$t1=&$f->create('T1');
echo $t1->getName();
echo $config;
?>
f.inc.php

<?php
class factory
{
 function factory()
 {
  $this->mClasses=array('T1'=>'t1.inc.php','T2'=>'t2.inc.php');
 }
 function &create($class)
 {
  if (!class_exists($class))
  {
   require_once($this->mClasses[$class]);
  }
  return new $class;
 }
}
?>
t1.inc.php

<?php
global $config;
$config='surfchen';
class T1
{
 var $mName='name::T1';
 function getName()
 {
  return $this->mName;
 }
}
?>
t2.inc.php

<?php
class T2
{
 function T2()
 {
  echo 't2 is ok';
 }
}
?>

class Mysql{
    public static $conn;
    public static function getInstance(){
        if (!self::$conn){
            new self();
            return self::$conn;
        }else {
            return self::$conn;
        }
       
    }
    private  function __construct(){   
        self::$conn=  "mysql_connect:";//    mysql_connect('','','')   
    }
   
    public function __clone()
    {
        trigger_error("Only one connection");
    }
}

echo Mysql::getInstance();
echo Mysql::getInstance();
 

<?php
$filename = 'test.txt';
if (is_writable($filename)) {
  echo 'The file is writable';
} else {
  echo 'The file is not writable';
}
?> 

/*
  问题出现：如何检查一个目录是否可写，如何目录下还有目录和文件，那么都要检查
   
  思路：
   （1）首先先写出检查空目录是否可写的算法：
         在该目录中生成一个文件，如果不能生成，表明该目录没有写的权限
   
   （2）使用递归的办法来进行检查
  
  代码实现：
 */
  set_time_limit(1000);
  function check_dir_iswritable($dir_path){
  $dir_path=str_replace('\','/',$dir_path);
  $is_writale=1;
  if(!is_dir($dir_path)){
    $is_writale=0;
    return $is_writale;
  }else{
   $file_hd=@fopen($dir_path.'/test.txt','w');
   if(!$file_hd){
    @fclose($file_hd);
    @unlink($dir_path.'/test.txt');
    $is_writale=0;
    return $is_writale;
   }
   $dir_hd=opendir($dir_path);
   while(false!==($file=readdir($dir_hd))){
    if ($file != "." && $file != "..") {
     if(is_file($dir_path.'/'.$file)){
      //文件不可写，直接返回
      if(!is_writable($dir_path.'/'.$file)){
       return 0;
      } 
     }else{
      $file_hd2=@fopen($dir_path.'/'.$file.'/test.txt','w');
      if(!$file_hd2){
       @fclose($file_hd2);
       @unlink($dir_path.'/'.$file.'/test.txt');
       $is_writale=0;
       return $is_writale;
      }
      //递归
      $is_writale=check_dir_iswritable($dir_path.'/'.$file);
     }
    }
   }
  }
  return $is_writale;
  }

<?php
    //测试时文件的编码方式要是UTF8
    $str='中文a字1符';
    echo strlen($str).'<br>';//14
    echo mb_strlen($str,'utf8').'<br>';//6
    echo mb_strlen($str,'gbk').'<br>';//8
    echo mb_strlen($str,'gb2312').'<br>';//10
?>

<?php
$str = '我是一串比较长的中文-';

echo "mb_substr:" . mb_substr($str, 0, 6, 'utf-8');

echo "<br>";

echo "mb_strcut:" . mb_strcut($str, 0, 6, 'utf-8');
?>

/**
 * 字符串分割 按字分割
 * @param $content string
 * @param $length int
 * @param $etc string
 * @return string
 */
 function Truncate($content, $length, $etc = '...') {

        if ($length == 0) {
            return '';
        } elseif (mb_strlen($content,'utf-8') > $length) {
            $length -= min($length, mb_strlen($etc));
            $charset = 'utf-8';
            $content = mb_substr($content, 0, $length, $charset) . $etc;
        }
        return $content;
    }

    $str ='伏尔泰（1694～1778）法国资产阶级启蒙思想家，哲学家，史学家，文学家。伏尔泰原名F.M.阿鲁埃。';

    echo strlen($str);//字符串长度
 echo '<hr/>';
    echo mb_strlen($str,'utf-8');//字符串长度
 echo '<hr/>';
 echo mb_strcut($str,0,35,'utf-8');//按字节分割
 echo '<hr/>';
 echo mb_substr($str,0,35,'utf-8');//按字 分割
 echo '<hr/>';
    echo Truncate($str,35);//字符串截取方法