使用 fseek 逐行向后读取文件 [英] Read a file backwards line by line using fseek

问题描述

如何使用 fseek 逐行向后读取文件?

How do I read a file backwards line by line using fseek?

代码可能会有所帮助.必须是跨平台和纯php.

code can be helpful. must be cross platform and pure php.

非常感谢

问候

杰拉

推荐答案

问题在于使用 fseek，所以只能假设性能是一个问题，而 file() 不是解决方案.这是使用 fseek 的简单方法:

The question is asking using fseek, so can only assume that performance is an issue and file() is not the solution. Here is a simple approach using fseek:

我的文件.txt

#file.txt
Line 1
Line 2
Line 3
Line 4
Line 5

和代码:

<?php

$fp = fopen('file.txt', 'r');

$pos = -2; // Skip final new line character (Set to -1 if not present)

$lines = array();
$currentLine = '';

while (-1 !== fseek($fp, $pos, SEEK_END)) {
    $char = fgetc($fp);
    if (PHP_EOL == $char) {
            $lines[] = $currentLine;
            $currentLine = '';
    } else {
            $currentLine = $char . $currentLine;
    }
    $pos--;
}

$lines[] = $currentLine; // Grab final line

var_dump($lines);

输出:

array(5) {
   [0]=>
   string(6) "Line 5"
   [1]=>
   string(6) "Line 4"
   [2]=>
   string(6) "Line 3"
   [3]=>
   string(6) "Line 2"
   [4]=>
   string(6) "Line 1"
}

您不必像我一样附加到 $lines 数组，如果这是脚本的目的，您可以立即打印输出.如果您想限制行数，也很容易引入计数器.

You don't have to append to the $lines array like I am, you can print the output straight away if that is the purpose of your script. Also it is easy to introduce a counter if you want to limit the number of lines.

$linesToShow = 3;
$counter = 0;
while ($counter <= $linesToShow && -1 !== fseek($fp, $pos, SEEK_END)) {
   // Rest of code from example. After $lines[] = $currentLine; add:
   $counter++;
}

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