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HomeBackend DevelopmentPHP TutorialPHP中strlen()和mb_strlen()的区别浅析_PHP

在php中常见的计算字符串长度的函数有:strlen和mb_strlen.当字符全是英文字符的时候,两者是一样。这里主要比较一下,中英文混排的时候,两个计算结果。

先来看一个例子:

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

结果分析:在strlen计算时,对待一个UTF8的中文字符是3个长度,所以“中文a字1符”长度是3*4+2=14,在mb_strlen计算时,选定内码为UTF8,则会将一个中文字符当作长度1来计算,所以“中文a字1符”长度是6。

利用这两个函数则可以联合计算出一个中英文混排的串的占位是多少(一个中文字符的占位是2,英文字符是1)
复制代码 代码如下:
echo (strlen($str) + mb_strlen($str,'UTF8')) / 2;

例如:“中文a字1符” 的strlen($str)值是14,mb_strlen($str)值是6,则可以计算出“中文a字1符”的占位是10:


PHP内置的字符串长度函数strlen无法正确处理中文字符串,它得到的只是字符串所占的字节数。

对于GB2312的中文编码,strlen得到的值是汉字个数的2倍,而对于UTF-8编码的中文,就是3倍的差异了(在UTF-8编码下,一个汉字占3个字节)。

采用mb_strlen函数可以较好地解决这个问题。

mb_strlen的用法和 strlen类似,只不过它有第二个可选参数用于指定字符编码。

例如得到UTF-8的字符串$str长度,可以用mb_strlen($str,'UTF-8')。如果省略第二个参数,则会使用PHP的内部编码。内部编码可以通过mb_internal_encoding()函数得到。

注意: mb_strlen并不是PHP核心函数,使用前需要确保在php.ini中加载了php_mbstring.dll
即确保“extension=php_mbstring.dll”这一行存在并且没有被注释掉,否则会出现未定义函数的问题。

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