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    ▪php通过文件头检测文件类型通用代码类（zip,rar等)       有时候我们这样做还不完善。可能有些人上存一些文件，但是他通过修改扩展名，让在我们的文件类型之内。 单实际访问时候又不能展示（因为扩展名与文件内容不符）。下面这个php类，.........

    ▪php empty,isset,is_null判断比较（差异与异同）       一、举例说明 A.一个变量没有定义，我们该怎么样去判断呢 代码如下: <?php #不存在$test 变量 $isset= isset($test)?"test is define!":"test is undefine!"; echo "isset:$isset\r\n"; $empty=!empty($test)?"test is define!":.........

    ▪学习php笔记 字符串处理       substr(); substr(str,start,length); 例：substr('php is very good language',4,5); 输出为 is ve; 当start>str的长度，则返回为（）； substr('php is very good language',26,5); substr('php is very good language',4); 输出为 （空白.........

代码如下:

<?php
/*通过文件名，获得文件类型*
*@author chengmo*
*@copyright cnblog.com/chengmo 2010-10-17
*@version 0.1
*$filename="d:/1.png";echo cFileTypeCheck::getFileType($filename); 打印：png
*/
class cFileTypeCheck
{
private static $_TypeList=array();
private static $Checkother";
if(!file_exists($filename)) throw new Exception("no found file!");
$file = @fopen($filename,"rb");
if(!$file) throw new Exception("file refuse!");
$bin = fread($file, 15); //只读15字节 各个不同文件类型，头信息不一样。
fclose($file);
$typelist=self::$_TypeList;
foreach ($typelist as $v)
{
$blen=strlen(pack("H*",$v[0])); //得到文件头标记字节数
$tbin=substr($bin,0,intval($blen)); ///需要比较文件头长度
if(strtolower($v[0])==strtolower(array_shift(unpack("H*",$tbin))))
{
return $v[1];
}
}
return $filetype;
}
/**
*得到文件头与文件类型映射表*
*
* @return array array(array('key',value)...)
*/
public function getTypeList()
{
return array(array("FFD8FFE1","jpg"),
array("89504E47","png"),
array("47494638","gif"),
array("49492A00","tif"),
array("424D","bmp"),
array("41433130","dwg"),
array("38425053","psd"),
array("7B5C727466","rtf"),
array("3C3F786D6C","xml"),
array("68746D6C3E","html"),
array("44656C69766572792D646174","eml"),
array("CFAD12FEC5FD746F","dbx"),
array("2142444E","pst"),
array("D0CF11E0","xls/doc"),
array("5374616E64617264204A","mdb"),
array("FF575043","wpd"),
array("252150532D41646F6265","eps/ps"),
array("255044462D312E","pdf"),
array("E3828596","pwl"),
array("504B0304","zip"),
array("52617221","rar"),
array("57415645","wav"),
array("41564920","avi"),
array("2E7261FD","ram"),
array("2E524D46","rm"),
array("000001BA","mpg"),
array("000001B3","mpg"),
array("6D6F6F76","mov"),
array("3026B2758E66CF11","asf"),
array("4D546864","mid"));
}
public static function getFileType($filename)
{
if(!self::$CheckClass) self::$Checkcodetitle"> 代码如下:

$filename="d:/1.png";
echo $filename,"\t",cFileTypeCheck::getFileType($filename),"\r\n";
$filename="d:/test.doc";
echo $filename,"\t",cFileTypeCheck::getFileType($filename),"\r\n";
d:/1.png png
d:/test.doc xls/doc

代码如下:

<?php
#不存在$test 变量

$isset= isset($test)?"test is define!":"test is undefine!";
echo "isset:$isset\r\n";

$empty=!empty($test)?"test is define!":"test is undefine!";
echo "empty:$empty\r\n";

$is_null=is_null($test)?"test is define!":"test is undefine!";
echo "is_null:$is_null\r\n";

代码如下:

<?php
$a=100;
$b="";
$c=null;
//isset检查
echo "isset","\$a=$a",isset($a)?"define":"undefine","\r\n";
echo "isset","\$b=$b",isset($b)?"define":"undefine","\r\n";
echo "isset","\$c=$c",isset($c)?"define":"undefine","\r\n";
unset($b);
echo "isset","\$b",isset($b)?"define":"undefine","\r\n";
$b=0;
echo "\r\n\r\n";

//empty检查
echo "empty","\$a=$a",!empty($a)?"no empty":"empty","\r\n";
echo "empty","\$b=$b",!empty($b)?"no empty":"empty","\r\n";
echo "empty","\$c=$c",!empty($c)?"no empty":"empty","\r\n";
unset($b);
echo "empty","\$b",!empty($b)?"no empty":"empty","\r\n";
$b=0;
echo "\r\n\r\n";

//is_null检查
echo "is_null","\$a=$a",!is_null($a)?"no null":"null","\r\n";
echo "is_null","\$b=$b",!is_null($b)?"no null":"null","\r\n";
echo "is_null","\$c=$c",!is_null($c)?"no null":"null","\r\n";
unset($b);
echo "is_null","\$b",is_null($b)?"no null":"null","\r\n";

代码如下:

<?php
function checkNull($a)
{
if(array_key_exists($a,$GLOBALS))
{
global $$a;
if(is_null($$a))
return true;
}
return false;
}
$test=null;
var_dump(checkNull("test"));
var_dump(checkNull("test1"));