ftruncate

(PHP 4, PHP 5)

ftruncateReduz um arquivo a um tamanho especificado

Descrição

bool ftruncate ( resource $handle , int $size )

Pega o ponteiro de arquivo handle e reduz o arquivo ao comprimento size.

Parâmetros

handle

O ponteiro do arquivo.

Nota:

O ponteiro handle deve estar aberto para escrita.

size

O tamanho pro qual reduzir.

Nota:

Se size for maior que o arquivo, o arquivo será estendido com bytes nulos.

Se size for menor, os dados extras serão perdidos.

Valor Retornado

Retorna TRUE em caso de sucesso ou FALSE em caso de falha.

Changelog

Versão Descrição
PHP 4.3.3 Antes desta versão, ftruncate() retornava integer no valor 1 no caso de sucesso, ao invés de boolean TRUE.

Notas

Nota:

O ponteiro do arquivo não é alterado.

Veja Também

  • fopen() - Abre um arquivo ou URL
  • fseek() - Procura (seeks) em um ponteiro de arquivo

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User Contributed Notes 3 notes

up
3
emailfire at gmail dot com
3 years ago
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);
?>
up
3
rc at opelgt dot org
6 years ago
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.
up
-2
eurosat7 at yahoo dot de
3 years ago
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. ;)
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