1 function sub_str($str, $length = 0, $append = true)
 2 {
 3     $str = trim($str);
 4     $strlength = strlen($str);
 5 
 6     if ($length == 0 || $length >= $strlength)
 7     {
 8         return $str;  //截取长度等于0或大于等于本字符串的长度，返回字符串本身
 9     }
10     elseif ($length < 0)  //如果截取长度为负数
11     {
12         $length = $strlength + $length;//那么截取长度就等于字符串长度减去截取长度
13         if ($length < 0)
14         {
15             $length = $strlength;//如果截取长度的绝对值大于字符串本身长度，则截取长度取字符串本身的长度
16         }
17     }
18 
19     if (function_exists('mb_substr'))
20     {
21         $newstr = mb_substr($str, 0, $length, EC_CHARSET);
22     }
23     elseif (function_exists('iconv_substr'))
24     {
25         $newstr = iconv_substr($str, 0, $length, EC_CHARSET);
26     }
27     else
28     {
29         //$newstr = trim_right(substr($str, 0, $length));
30         $newstr = substr($str, 0, $length);
31     }
32 
33     if ($append && $str != $newstr)
34     {
35         $newstr .= '...';
36     }
37 
38     return $newstr;
39 }