前者是后者的：3 倍！
多次刷新页面的话，可以发现标准函数的执行效率基本上是自己的函数的 3 倍！当然，标准的函数中使用了 PHP 的内置函数: str_split()，implode()，所以要比自己写函数快得多，对 str_split() 函数没有印象？来看看手册解释：
str_split -- Convert a string to an array(将一个字符串转换成数组)
函数描述：
array str_split ( string string [, int split_length] )
Converts a string to an array. If the optional split_length parameter is specified, the returned array will be broken down into chunks with each being split_length in length, otherwise each chunk will be one character in length.
FALSE is returned if split_length is less than 1. If the split_length length exceeds the length of string, the entire string is returned as the first (and only) array element.
例 1. Example uses of str_split()
<?php
$str = "Hello Friend";
$arr1 = str_split($str);
$arr2 = str_split($str, 3);
print_r($arr1);
print_r($arr2);
?>
Output may look like:
Array
(
[0] => H
[1] => e
[2] => l
[3] => l
[4] => o
[5] =>
[6] => F
[7] => r
[8] => i
[9] => e
[10] => n
[11] => d
)
Array
(
[0] => Hel
[1] => lo
[2] => Fri
[3] => end
)
