ftruncate

(PHP 4, PHP 5)

ftruncate — Przycina plik do podanej długości

Opis

bool ftruncate ( resource $uchwyt , int $rozmiar )

Pobiera wskaźnik pliku, uchwyt i przycina plik do długości, rozmiar.

Parametry

uchwyt: Wskaźnik pliku

Informacja:
uchwyt musi by otworzony do zapisu.
rozmiar: Rozmiar do którego przycinamy.

Informacja:
Jeśli rozmiar jest większy niż rozmiar pliku to jest on rozszerzany bajtami null.

Jeśli rozmiar jest mniejszy niż rozmiar pliku to dalsze dane zostaną stracone.

Zwracane wartości

Zwraca TRUE w przypadku powodzenia, FALSE w przypadku błędu.

Rejestr zmian

Wersja	Opis
PHP 4.3.3	Przed tym wydaniem ftruncate() zwracała integer o wartości 1 w przypadku sukcesu, zamiast boolean `TRUE`.

Notatki

Informacja:
Wskaźnik pliku jest nie modyfikowany.

Zobacz też:

fopen() - Otwiera plik lub URL
fseek() - Seeks on a file pointer

fwrite

ftell

[edit] Last updated: Fri, 23 Mar 2012

add a note User Contributed Notes ftruncate

emailfire at gmail dot com 16-Jun-2011 02:14


If you want to empty a file of it's contents bare in mind that opening a file in w mode truncates the file automatically, so instead of doing...



<?php

$fp = fopen("/tmp/file.txt", "r+");

ftruncate($fp, 0);

fclose($fp);

?>



You can just do...



<?php

$fp = fopen("/tmp/file.txt", "w");

fclose($fp);

?>

eurosat7 at yahoo dot de 21-Apr-2011 08:31


If you want to ftruncate but keep the end:

<?php

    function ftruncatestart($filename,$maxfilesize){

        $size=filesize($filename);

        if ($size<$maxfilesize*1.0) return;

        $maxfilesize=$maxfilesize*0.5; //we don't want to do it too often...

        $fh=fopen($filename,"r+");

        $start=ftell($fh);

        fseek($fh,-$maxfilesize,SEEK_END);

        $drop=fgets($fh);

        $offset=ftell($fh);

        for ($x=0;$x<$maxfilesize;$x++){

            fseek($fh,$x+$offset);

            $c=fgetc($fh);

            fseek($fh,$x);

            fwrite($fh,$c);

        }

        ftruncate($fh,$maxfilesize-strlen($drop));

        fclose($fh);

    }

?>

It will not just cut it but search for a newline so you avoid corrupting your csv or logfiles. But I don't know if you will stress the reading head of your drive. ;)

yetihehe at yetihehe dot com 22-Apr-2010 03:12


Simple script which will delete spaces from end of php files (suitable in big sites, when you are including many files before sending headers and without output buffering):





<?php


function mapfiles($func,$filename,$level=0) {


  if(is_dir($filename)) {


    if($level>30) return; //limit recurence in case of looped dirs


    $handle=opendir($filename);


    while(($dirname=readdir($handle))!==false) {


      if($dirname=='.'||$dirname=='..') continue;


      mapfiles($func,$filename.'/'.$dirname,$level+1);


    }


    closedir($handle);


  } else {


    $func($filename);


  }


}





function scanfile($filename) {


  if(substr($filename,-4)!=".php") return;


  $ff=fopen($filename,"r+");


  fseek($ff, -10, SEEK_END);


  $str=fread($ff,12);


  $matches=array();


  if(preg_match('/\?>(\s+)$/',$str,$matches)) {


    $fsize=filesize($filename);


    ftruncate($ff, $fsize-strlen($matches[1]));


  }


  fclose($ff);


}





mapfiles("scanfile",".");


?>

rc at opelgt dot org 05-Jan-2008 10:49


Writing after ftruncate



I didnt expect that I can write in the middle of nowhere. I thought that I would write at the beginning of the file but the first 4 bytes were filled automatically with NULLs followed by "56":



<?php

$str1  = 1234;

$str2  =   56;

$datei = "test.txt";



$dh = fopen($datei,"w");

fwrite($dh, $str1);

fclose($dh);



$dh = fopen ($datei,"r+");

echo "content: ".fread($dh, filesize($datei))."<br>";

echo "pointer after fread at: ".ftell($dh)."<br>";

ftruncate($dh, 0);

echo "pointer after truncate at: ".ftell($dh)."<br>";

fwrite($dh, $str2);

echo "pointer after fwrite at: ".ftell($dh)."<br>";

rewind($dh);

echo "pointer after rewind at: ".ftell($dh)."<br>";

$str = fread($dh, 6);

echo "content: $str<br>in ASCII: ";

for($i = 0; $i < 6; $i++)

 echo ord($str{$i})."-";

fclose($dh);



/*

   OUTPUT:

   content: 1234

   pointer after fread at: 4

   pointer after truncate at: 4

   pointer after fwrite at: 6

   pointer after rewind at: 0

   content: 56

   in ASCII: 0-0-0-0-53-54

*/

?>



So not only ftruncate is filling an empty file up with NULLs as in the note before. Fread is filling leading space with NULLs too.

mike at mikeleigh dot com 04-Jan-2007 12:30


I have produced a number of tests below which walk through my findings of the ftruncate function.  For the impatient among you ftruncate can be used to increase the size of the file and will fill the rest of the file with CHR 0 or ASCII NULL.  It can be used as a very convenient way of making a 1Mb file for instance.



Test 1

<?php

/*

  Test 1: Write "some text" to a file.

  Result: The text "some text" should be present in test_1.txt

*/

$fp = fopen('test_1.txt', 'w+');

fwrite($fp, 'some text');

?>

The first test is only here to make sure that a file can be written with some text.



Test 2

<?php

/*

  Test 2: Write "some text" to a file and ftruncate the file to 4 bytes.

  Result: The text "some" should be present in test_2.txt as the file will have been truncated to 4 bytes.

*/

$fp = fopen('test_2.txt', 'w+');

fwrite($fp, 'some text');

ftruncate($fp, 4);

?>

As expected the file has been truncated to 4 bytes.



Test 3

<?php

/*

  Test 3: Write "some text" to a file and ftruncate the file to 40 bytes.

  Result: The text "some text" should be present in test_3.txt as the file will have been truncated to 40 bytes.

*/

$fp = fopen('test_3.txt', 'w+');

fwrite($fp, 'some text');

ftruncate($fp, 40);

?>

Interestingly the file has increased from 9 bytes to 40 bytes.  The remaining 31 bytes of the file are ASCII code 0 or NULL though.



Further notes can be found here http://mikeleigh.com/links/ftruncate

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