php实现读取超大文件的方法

<?php
/**
 * 取文件最后$n行
 * 
 * @param string $filename 文件路径
 * @param int $n 最后几行
 * @return mixed false表示有错误，成功则返回字符串
 */
function FileLastLines($filename, $n){
   if(!$fp = fopen($filename, 'r')){
    echo "打开文件失败，请检查文件路径是否正确，路径和文件名不要包含中文";
    return false;
    }
  $pos = -2;
  $eof = "";
  $str = "";
  while($n > 0){
    while($eof != "n"){
      if(!fseek($fp, $pos, SEEK_END)){
        $eof = fgetc($fp);
        $posC;
        }else{
        break;
        }
      }
    $str .= fgets($fp);
    $eof = "";
    $nC;
    }
  return $str;
  }

echo nl2br(FileLastLines('sss.txt', 4));
/**
 * * * 取文件最后$n行 *
 * 
 * @param string $filename 文件路径 *
 * @param int $n 最后几行 *
 * @return mixed false表示有错误，成功则返回字符串
 */
function FileLastLines($filename, $n){
  if(!$fp = fopen($filename, 'r')){
    echo "打开文件失败，请检查文件路径是否正确，路径和文件名不要包含中文";
    return false;
    }
  $pos = -2;
  $eof = "";
  $str = "";
  while($n > 0){
    while($eof != "n"){
      if(!fseek($fp, $pos, SEEK_END)){
        $eof = fgetc($fp);
        $pos--;
        }else{
        break;
        }
      }
    $str .= fgets($fp);
    $eof = "";
    $n--;
    }
  return $str;
  }
echo nl2br(FileLastLines('sss . txt', 4));

function tail($fp, $n, $base = 5)
{
  assert($n > 0);
  $pos = $n + 1;
  $lines = array();
  while(count($lines) < = $n){
    try{
      fseek($fp, - $pos, SEEK_END);
      }
    catch (Exception $e){
      fseek(0);
      break;
      }
    $pos *= $base;
    while(!feof($fp)){
      array_unshift($lines, fgets($fp));
      }
    }
  return array_slice($lines, 0, $n);
  }
var_dump(tail(fopen("access.log", "r+"), 10));
$fp = fopen($file, "r");
$line = 10;
$pos = -2;
$t = " ";
$data = "";
while ($line > 0){
  while ($t != "n"){
    fseek($fp, $pos, SEEK_END);
    $t = fgetc($fp);
    $pos --;
    }
  $t = " ";
  $data .= fgets($fp);
  $line --;
  }
fclose ($fp);
echo $data;
?>