问题是代码给了 pack() (我指的是最后一个参数)一个字符，一个数组, 和一个整数.由于代码 C 需要 4 个字符，这就是错误的原因.

The problem is that the code is giving to pack() (I am referring the the last arguments) a character, an array, and an integer. As the code C wants 4 characters, that is the cause of the error.

代码应该类似于

$split = preg_split('/\./','10.2.1.1', -1, PREG_SPLIT_NO_EMPTY);
echo pack("SSA12AC4L",
  '25',
  '00001',
  '2u7wx6fd94fd',
  'f',
  $split[0],
  $split[1],
  $split[2],
  $split[3],
  time()+60*60
);

那么，在这种情况下没有理由使用 preg_split()，当可以使用 explode() 代替时.正则表达式应仅在绝对必要时使用，因为与其他字符串函数相比，正则表达式函数速度较慢.

Then, there is no reason to use preg_split() in this case, when explode() can be used instead. Regular expressions should be used only when strictly necessary because the regular expression functions are slower, compared to other string functions.