Detailed explanation of sample code for php to intercept n characters starting at a certain position in a GBK document

The following editor will bring you a php method to intercept n characters starting at a certain position in the GBK document. The editor thinks it is quite good, so I will share it with you now and give it as a reference for everyone. Let’s follow the editor to take a look.

cut.php：

#!/usr/bin/php
<?php
define(&#39;INPUT_FILE&#39;, &#39;t.txt&#39;);
define(&#39;OUTPUT_FILE&#39;, &#39;a.txt&#39;);
$pos = max(intval($argv[1]), 0); 
$len = max(intval($argv[2]), 0); 
$file_size = filesize(INPUT_FILE);
if($pos >= $file_size) exit;
$fp = fopen(INPUT_FILE, &#39;rb&#39;);
$point = 0; //current byte position
$string = &#39;&#39;; 
while(ftell($fp) < $file_size) {
  if($point >= $pos + $len) break;$byte = fread($fp, 1); 
  //php version >= 5.4
  $char = unpack(&#39;C&#39;, $byte)[1];
  if($char <= 0x7f) {
    //single byte
    if($point >= $pos) $string .= $byte;
    $point += 1;
    continue;
  } else {
    //double bytes
    if($point >= $pos) {
      $string .= $byte.fread($fp, 1); 
    } else {
      fseek($fp, 1, SEEK_CUR);
    }
    $point += 1;
    continue;
  }  
}
fclose($fp);
file_put_contents(OUTPUT_FILE, $string);
?>

Source file t.txt content:

dkei20王nnso

Test command:

./cut.php 6 1

View results:

hexdump -C t.txt && hexdump -C a.txt

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