/**
* 隱藏部分字符串
* # 此方法多用于手機號碼或身份證號、銀行卡號的中間部分數字的隱藏
*/
function func_substr_replace($str, $replacement = '*', $start = 1, $length = 3)
{
  $len = mb_strlen($str,'utf-8');
  if ($len > intval($start+$length)) {
    $str1 = mb_substr($str,0,$start,'utf-8');
    $str2 = mb_substr($str,intval($start+$length),NULL,'utf-8');
  } else {
    $str1 = mb_substr($str,0,1,'utf-8');
    $str2 = mb_substr($str,$len-1,1,'utf-8');
    $length = $len - 2;
  }
  $new_str = $str1;
  for ($i = 0; $i  $length; $i++) {
    $new_str .= $replacement;
  }
  $new_str .= $str2;
  return $new_str;
}

/**
 * 只保留字符串首尾字符，隱藏中間用*代替（兩個字符時只顯示第一個）
 * @param string $user_name 姓名
 * @return string 格式化后的姓名
 */
function substr_cut($user_name){
  $strlen   = mb_strlen($user_name, 'utf-8');
  $firstStr   = mb_substr($user_name, 0, 1, 'utf-8');
  $lastStr   = mb_substr($user_name, -1, 1, 'utf-8');
  return $strlen == 2 ? $firstStr . str_repeat('*', mb_strlen($user_name, 'utf-8') - 1) : $firstStr . str_repeat("*", $strlen - 2) . $lastStr;
}