substr,mb_substr,mb_strcut,详解与中文字符串的截取无乱码

substr截取中文字符串会出现乱码，substr是按照单字节截取的，

mb_substr,mb_strcut都可以截取中文字符串，其中mb_substr是按照字符的个数截取（包括中文字符）,mb_strcut是按照字节截取；

$str='水电费22sf223飞说的法士大夫24234是福施福士大夫';
echo mb_strcut($str, 0, 17, 'utf-8').'1<br />';//输出:水电费22sf223
echo mb_strcut($str, 3, 17, 'utf-8').'2<br />';//输出:电费22sf223飞
echo mb_strcut($str, -3, -2, 'utf-8').'3<br />';//输出:空值
echo mb_strcut($str, -3, 2, 'utf-8').'4<br />';//输出:空值
echo mb_strcut($str, 3, -2, 'utf-8').'5<br />';//输出:电费22sf223飞说的法士大夫24234是福施福士大

$str='水电费22sf223飞说的法士大夫24234是福施福士大夫';
echo mb_substr($str, 0, 17, 'utf-8').'<br />';//输出:水电费22sf223飞说的法士大夫
echo mb_substr($str, 3, 17, 'utf-8').'<br />';//输出:费22sf223飞说的法士大夫242
echo mb_substr($str, -3, -2, 'utf-8').'<br />';//输出:福士
echo mb_substr($str, -3, 2, 'utf-8').'<br />';//输出:士大
echo mb_substr($str, 3, -2, 'utf-8').'<br />';//输出:22sf223飞说的法士大夫24234是福施福士

echo "<br /><br />";
$str='234sdh24324shkfsdfsdf';
echo substr($str,0,2).'<br />';//输出:23
echo substr($str,3,3).'<br />';//输出:sdh
echo substr($str,-7,3).'<br />';//输出:fsd
echo substr($str,-3).'<br />';//输出:sdf
echo substr($str,-3,-6).'<br />';//输出:空值
echo substr($str,-6,-3).'<br />';//输出:sdf
echo substr($str,3,-2).'<br />';//输出:sdh24324shkfsdfs

php扩展函数一般比自定义的字符串函数速度快，比如下面这个自定义函数就比php自带的函数慢5到6倍；

$str='水电费22sf223飞说的法士大夫24234是福施福士大夫';
echo cutstr($str, 17, $suffix = '');
function cutstr($string, $length, $suffix = '')
{
$p    =    0;
$j    =    0;
if($string == "")
{
return "";
}
preg_match_all('/([x41-x5a,x61-x7a,x30-x39])/', $string, $letter); //字母
$string_len = strlen($string);
$let_len = count($letter[0]);
if($string_len == $let_len)
{
//没有汉字
$len = floor($length / 2);
if($string_len > $len)
return substr($string, 0, $len) . $suffix;
else
return substr($string, 0, $len);
}
$length_tmp    =    ($string_len - $let_len * 2) + $let_len * 2;
if($length_tmp > $length)
{
for ($k=0;$k<=($length-3);$k++)
{
$j++;
if($j    >    ($length-3))
{
break;
}
if (ord(substr($string,$k,1)) >= 129)
{
$k+=2;
$j+=2;
}
else
{
$p++;
}
if($p    ==    2)
{
$j++;
$p    =    0;
}
}
$string = substr($string, 0, $k);
}
$string    =    str_replace("<BR…","<BR>…",$string);
$string    =    str_replace("<B…","<BR>…",$string);
$string    =    str_replace("<…","<BR>…",$string);

if($string_len > strlen($string))
return $string . $suffix;
else
return $string;
}