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详解PHP中的mb_detect_encoding函数使用方法

Jun 06, 2016 pm 07:48 PM
php

这篇文章主要介绍了详解PHP中的mb_detect_encoding函数使用方法,包括对字符串编码的转换和判断以及Call to undefined function mb_detect_encoding()错误的解决,

php中可以使用 mb_detect_encoding() 函数来判断字符串是什么编码的。

当在php中使用mb_detect_encoding函数进行编码识别时,很多人都碰到过识别编码有误的问题,例如对与GB2312和UTF-8,或者UTF-8和GBK(这里主要是对于cp936的判断),网上说是由于字符短时mb_detect_encoding会出现误判。

代码如下:
 

$encode = mb_detect_encoding($keytitle, array("ASCII","UTF-8","GB2312","GBK","BIG5")); if($encode == "UTF-8"){ $keytitle = iconv("UTF-8","GBK",$keytitle); }

这段代码的作用是检测字符串的编码是否UTF-8,是的话就转换为GBK。
可是当 $keytitle = “%D0%BE%C6%AC”;时。检测结果却是UTF-8.这个bug其实不算是bug,写程序时也不应当过于依赖mb_detect_encoding,当字符串较短时,检测结果产生偏差的可能性很大。
解决办法,代码如下:
 

$encode = mb_detect_encoding($keytitle, array("ASCII","GB2312","GBK","UTF-8");

三个参数分别是:被检测的输入变量、编码方式的检测顺序(一旦为真,后面自动忽略)、strict模式对编码检测的顺序进行调整,将最大可能性放在前面,这样减少被错误转换的机会。
一般要先排gb2312,当有GBK和UTF-8时,需要将常用的排列到前面。

PHP字符串编码的转换和判断


GBK 和 UTF-8 编码的转换是一个非常恶心的事情,,比如像 PHP 中的 json_encode 本身根本不支持 GBK 形式的编码。有两个库函数能够支持编码的转换,通常能够想到的就是 iconv 函数,使用起来也非常爽:
 
iconv('GBK', 'UTF-8//IGNORE', '测试字符串'); // 将字符串由 GBK 编码转换为 UTF-8 编码

但 iconv 只能解决编码预先知道的情况,如果字符串编码未知,则需要先探测其编码,这时可能会用到 mb_string 扩展库:
 
mb_detect_encoding('测试字符串');

可是 mb_detect_encoding 存在一个硬伤,经常出现判断不准确的情况。或许这样就可以解决:

 

// 使用 iconv 转换并判断是否等值,效率不高 function is_utf8 ($str) { if ($str === iconv('UTF-8', 'UTF-8//IGNORE', $str)) { return 'UTF-8'; } } // 多种编码的情况 function detect_encoding ($str) { foreach (array('GBK', 'UTF-8') as $v) { if ($str === iconv($v, $v . '//IGNORE', $str)) { return $v; } } }

通过以上方式得到字符串编码信息后,就可以利用 iconv 或 mb_convert_encoding 来转换编码了。

Call to undefined function mb_detect_encoding()错误解决


Windows系统下:
一、Fatal error: Call to undefined function: iconv() in C:\Program Files\AppServ\www\...\xxx.php on line 82
php中有个iconv()函数用来进行字符编码转换
在php.ini文件中同样存在extension=php_iconv.dll
这样的声明才能保证这个函数正常使用
如果在php.ini文件中的extension=php_iconv.dll前面有分号
表示被注释掉了,如果存在分号就要去掉,并重新启动服务器
再次运行程序才能解决

二、Fatal error: Call to undefined function: mb_detect_encoding() in C:\Program Files\AppServ\www\...\xxx.php on line 1355
1、找到php扩展目录(我的php扩展目录的路径是:C:\Program Files\AppServ\php\extensions)
     在extensions目录下面找到php_mbstring.dll文件,
2、将php_mbstring.dll这个文件拷贝到php.ini文件所在的目录下(我的php.ini文件所在的目录:C:\WINDOWS)
3、用记事本打开php.ini文件,使用快捷键Ctrl+F查找extension=php_mbstring.dll
4、 如果php.ini文件中存在extension=php_mbstring.dll,去掉该行extension前面的分号,
      如果不存在,就在其他extension=...的下一行加入extension=php_mbstring.dll,
      最终记得保存php.ini文件
5.   重新启动你的Apache服务器

刚刚发现其实不拷贝php_mbstring.dll这个文件到php.ini所在目录也行

Linux系统下:

出现下面问题时:

PHP   1. {main}() /home/xu/web/whois/ab.cn.php:0
PHP   2. base_func->is_exist() /home/xu/web/whois/ab.cn.php:21
PHP   3. strftime() /home/xu/web/whois/whois.mysql.php:46
ab.cnis exist
PHP Fatal error:  Call to undefined function mb_detect_encoding() in /home/xu/web/whois/whois.main.php on line 98
在网上查找了各种资料后才知道原来是php-mbstring这个php插件没有安装(有些同学可能是没有在php.ini中起用此插件),写下此段文件以作笔记。

    首先使用yum或者apt安装mbstring.so,使用命令:yum install php-mbstring或者apt-get install php-mbstring (ubuntu用户最好使用apt-cache search mbstring搜索一番后再安装,软件名字可能有误)

    然后修改php.ini:执行vim /etc/php.ini,加入extension="/usr/lib/php/modules/mbstring.so"内容,后面的路径可能不一样,根据mbstring.so存放的目录做相应的修改即可。一般是不用更改的。

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