fwrite

(PHP 4, PHP 5)

fwriteEscrita binary-safe em arquivos

Descrição

int fwrite ( resource $handle , string $string [, int $length ] )

fwrite() escreve o conteúdo da string para o stream de arquivo apontado por handle.

Parâmetros

handle

A file system pointer resource that is typically created using fopen().

string

A string a ser escrita.

length

Se o argumento comprimento for dado, a escrita irá parar depois que comprimento bytes tenham sido escritos ou o final da string seja alcançado, o que vier primeiro.

Observe que se o argumento comprimento for dado, a opção de configuração magic_quotes_runtime será ignorada e nenhuma barra será removida da string.

Valor Retornado

fwrite() retorna o número de bytes escritos, ou FALSE em caso de erro.

Notas

Nota:

Em sistemas que diferenciam entre arquivos binários e texto (por exemplo Windows) o arquivo tem que ser aberto com 'b' incluído no parâmetro 'mode' na fopen().

Nota:

Se o handle foi aberto com fopen() em modo de adição, escritas com fwrite() são atômicas (a não ser que o tamanho da string exceda o tamanho de bloco do sistema de arquivos, em algumas plataformas, e contanto que o arquivo esteja em um sistema de arquivos local). Sendo assim, não há necessidade de bloquear um recurso com flock() antes de chamar fwrite(); todos os dados serão escritos sem interrupção.

Nota:

Se escrevendo duas vezes para o ponteiro do arquivo, então a informação será adicionado ao final do contéudo do arquivo, significando que o exemplo abaixo não funcionaria como esperado:

<?php
$fp 
fopen('data.txt''w');
fwrite($fp'1');
fwrite($fp'23');
fclose($fp);

// o conteúdo de 'data.txt' agora é 123 e não 23!
?>

Exemplos

Exemplo #1 Um simples exemplo de fwrite()

<?php
$filename 
'teste.txt';
$conteudo "Acrescentar isso ao arquivo\n";

// Primeiro vamos ter certeza de que o arquivo existe e pode ser alterado
if (is_writable($filename)) {

 
// Em nosso exemplo, nós vamos abrir o arquivo $filename
 // em modo de adição. O ponteiro do arquivo estará no final
 // do arquivo, e é pra lá que $conteudo irá quando o 
 // escrevermos com fwrite().
    
if (!$handle fopen($filename'a')) {
         echo 
"Não foi possível abrir o arquivo ($filename)";
         exit;
    }

    
// Escreve $conteudo no nosso arquivo aberto.
    
if (fwrite($handle$conteudo) === FALSE) {
        echo 
"Não foi possível escrever no arquivo ($filename)";
        exit;
    }

    echo 
"Sucesso: Escrito ($conteudo) no arquivo ($filename)";

    
fclose($handle);

} else {
    echo 
"O arquivo $filename não pode ser alterado";
}
?>

Veja Também

  • fread() - Leitura binary-safe de arquivo
  • fopen() - Abre um arquivo ou URL
  • fsockopen() - Abre um socket de conexão Internet ou de domínio Unix
  • popen() - Abre um processo como ponteiro de arquivo
  • file_get_contents() - Lê todo o conteúdo de um arquivo para uma string

add a note add a note

User Contributed Notes 26 notes

up
16
nate at frickenate dot com
4 years ago
After having problems with fwrite() returning 0 in cases where one would fully expect a return value of false, I took a look at the source code for php's fwrite() itself. The function will only return false if you pass in invalid arguments. Any other error, just as a broken pipe or closed connection, will result in a return value of less than strlen($string), in most cases 0.

Therefore, looping with repeated calls to fwrite() until the sum of number of bytes written equals the strlen() of the full value or expecting false on error will result in an infinite loop if the connection is lost.

This means the example fwrite_stream() code from the docs, as well as all the "helper" functions posted by others in the comments are all broken. You *must* check for a return value of 0 and either abort immediately or track a maximum number of retries.

Below is the example from the docs. This code is BAD, as a broken pipe will result in fwrite() infinitely looping with a return value of 0. Since the loop only breaks if fwrite() returns false or successfully writes all bytes, an infinite loop will occur on failure.

<?php
// BROKEN function - infinite loop when fwrite() returns 0s
function fwrite_stream($fp, $string) {
    for (
$written = 0; $written < strlen($string); $written += $fwrite) {
       
$fwrite = fwrite($fp, substr($string, $written));
        if (
$fwrite === false) {
            return
$written;
        }
    }
    return
$written;
}
?>
up
11
Anonymous
5 years ago
If you write with the pointer in the middle of a file, it overwrites what's there rather than shifting the rest of the file along.
up
3
dharris dot nospam at removethispart dot drh dot net
6 years ago
Some people say that when writing to a socket not all of the bytes requested to be written may be written. You may have to call fwrite again to write bytes that were not written the first time. (At least this is how the write() system call in UNIX works.)

This is helpful code (warning: not tested with multi-byte character sets)

function fwrite_with_retry($sock, &$data)
{
    $bytes_to_write = strlen($data);
    $bytes_written = 0;

    while ( $bytes_written < $bytes_to_write )
    {
        if ( $bytes_written == 0 ) {
            $rv = fwrite($sock, $data);
        } else {
            $rv = fwrite($sock, substr($data, $bytes_written));
        }

        if ( $rv === false || $rv == 0 )
            return( $bytes_written == 0 ? false : $bytes_written );

        $bytes_written += $rv;
    }

    return $bytes_written;
}

Call this like so:

    $rv = fwrite_with_retry($sock, $request_string);

    if ( ! $rv )
        die("unable to write request_string to socket");
    if ( $rv != strlen($request_string) )
        die("sort write to socket on writing request_string");
up
1
php at biggerthanthebeatles dot com
10 years ago
Hope this helps other newbies.

If you are writing data to a txt file on a windows system and need a line break. use \r\n . This will write hex OD OA.

i.e.
$batch_data= "some data... \r\n";
fwrite($fbatch,$batch_data);

The is the equivalent of opening a txt file in notepad pressing enter and the end of the line and saving it.
up
-1
chill at cuna dot org
9 years ago
In PHP 4.3.7 fwrite returns 0 rather than false on failure.
The following example will output "SUCCESS: 0 bytes written" for existing file test.txt:

$fp = fopen("test.txt", "rw");
if (($bytes_written = fwrite($fp, "This is a test")) === false) {
  echo "Unable to write to test.txt\n\n";
} else {
  echo "SUCCESS: $bytes_written bytes written\n\n";
}
up
-1
oktavianus dot programmer at gmail dot com
5 years ago
this the another sample to use fwrite with create a folder and create the txt file.

<?php
$mypath
="testdir\\subdir\\test";
mkdir($mypath,0777,TRUE);
$filename = $mypath.'\test.txt';
$handle = fopen($filename,"x+");
$somecontent = "Add this to the file Oktavianus";
fwrite($handle,$somecontent);
echo
"Success";
fclose($handle);
?>

please try...
Oktavianus
up
-1
Andi
11 years ago
[Ed. Note:
The runtime configuration setting auto_detect_line_endings should solve this problem when set to On.]

I figured out problems when writing to a file using \r as linebreak, after that file() wasn't able to read the data from that file.
Using \n solved the problem.
up
-1
chedong at hotmail dot com
11 years ago
the fwrite output striped the slashes if without length argument given, example:

<?php
$str
= "c:\\01.txt";
$out = fopen("out.txt", "w");
fwrite($out, $str);
fclose($out);
?>

the out.txt will be:
c:^@1.txt
the '\\0' without escape will be '\0' ==> 0x00.

the correct one is change fwrite to:
fwrite($out, $str, strlen($str));
up
-2
cutmaster at fearlesss dot com
7 years ago
For those who, like me, lost a lot of minutes (hours) to understand why fwrite doesn't create a real utf-8 file, here's the explanation I've found :

I tried to do something like this :
<?php
$myString
= utf8_encode("Test with accents éèàç");
$fh=fopen('test.xml',"w");
fwrite($fh,$myString);
fclose($fh);
?>

For a mysterious reason, the resulted file shows the accent without the utf-8 conversion.

I tried the binary, mode, etc. etc. And finally I've found it :
It seems that fwrite NEEDS to have the utf8_encode function INSIDE its parameters like this, to understand it must create a non-text only file :
<?php
$myString
= "Test with accents éèàç";
$fh=fopen('test.xml',"w");
fwrite($fh,utf8_encode($myString));
fclose($fh);
?>
Hope this will help
up
-1
Jake Roberts
11 years ago
Use caution when using:

$content = fread($fh, filesize($fh)) or die "Error Reading";

This will cause an error if the file you are reading is zero length.

Intead use:

if ( false === fread($fh, filesize($fh)) ) die "Error Reading";

Thus it will be successful on reading zero bytes but detect and error returned as FALSE.
up
-2
james at facepwn dot com
5 years ago
if (is_writable($filename)) {

Could also be

if (is_writable($filename) or die ("Can not write to ".$filename)) {
up
-3
Jon Haynes
3 years ago
Be careful of using reserved Windows filenames in fwrite operations.

<?php
$fh
= fopen('prn.txt', 'w');
fwrite($fh, 'wtf?');
echo
'done' . PHP_EOL;
?>

The above script will hang (tested on Windows 7) before it can echo 'done'.

This is due to another 'feature' of our favourite operating system where filenames like prn.xxx, con.xxx, com1.xxx and aux.xxx (with xxx being any filename extension) are Windows reserved device names. Attempts to create/read/write to these files hangs the interpreter.
up
-3
bahatest at ifrance doc com
8 years ago
[Editor's Note: No, you only need to use this if you want a BOM (Byte order mark) added to the document - most people do not.]

if you have to write a file in UTF-8 format, you have to add an header to the file like this :

<?php
$f
=fopen("test.txt", "wb");
$text=utf8_encode("a!");
// adding header
$text="\xEF\xBB\xBF".$text;
fputs($f, $text);
fclose($f);
?>
up
-2
zaccraven at junk.com
7 years ago
Use this to get a UTF-8 Unicode CSV file that opens properly in Excel:

$tmp = chr(255).chr(254).mb_convert_encoding( $tmp, 'UTF-16LE', 'UTF-8');
$write = fwrite( $filepath, $tmp );

Use a tab character, not comma, to seperate the fields in  the $tmp.

Credit for this goes to someone called Eugene Murai, I found this solution by him after searching for several hours.
up
-3
chad 0x40 herballure 0x2e com
6 years ago
Remember to check the return value of fwrite(). In particular, writing into a socket can return fewer bytes than requested, and you'll have to try again with the remainder of your data.
up
-3
ceo at l-i-e dot com
5 years ago
If you are trying to write binary/structured data (e.g., a 4-byte sequence for an (int)) to a file, you will need to use:
http://php.net/pack
up
-3
elinor_hust at REMOVETHIS dot hotmail dot com
6 years ago
Remember to use double-quotes when outputting special characters such as \n or they come out literally.

...
up
-4
MKP Dev
9 years ago
bluevd at gmail dot com mentioned a hit counter. In his/her implementation, the file is first opened, read, closed, then opened +truncated, then written, and closed again. An alternative to this is:
<?php
$file
= 'counter.txt or whatever';
$handle = fopen ($file, 'r+'); // Let's open for read and write
$count = int (fread ($handle, filesize ($file)));
// We don't want to think it's a string and try appending
echo "Number of hits $count";
rewind ($handle); // Go back to the beginning
/*
* Note that we don't have problems with 9 being fewer characters than
* 10 because we are always incrementing, so we will always write at
* least as many characters as we read
**/
fwrite ($handle, ++$count); // Don't forget to increment the counter
fclose ($handle); // Done
?>
up
-2
james at nicolson dot biz
9 years ago
I could'nt quite get MKP Dev hit counter to work.... this is how I modified it
<?
function hitcount()
{
$file = "counter.txt";
if ( !
file_exists($file)){
       
touch ($file);
       
$handle = fopen ($file, 'r+'); // Let's open for read and write
       
$count = 0;

}
else{
       
$handle = fopen ($file, 'r+'); // Let's open for read and write
       
$count = fread ($handle, filesize ($file));
       
settype ($count,"integer");
}
rewind ($handle); // Go back to the beginning
/*
* Note that we don't have problems with 9 being fewer characters than
  * 10 because we are always incrementing, so we will always write at
   * least as many characters as we read
    **/
fwrite ($handle, ++$count); // Don't forget to increment the counter
fclose ($handle); // Done

return $count;
}     
?>
up
-2
Will at EnigmaChannel dot com
9 years ago
Using fwrite to write to a file in your include folder...

PHP does not recognise the permissions setting for the file until you restart the server... this script works fine. (still have to create the blank text file first though...it is not created automatically) On OS X Server..
Using the 1 in fopen tells php to look for the file in your include folder. Change your include folder by altering include_path in php.ini
On OS X Server, php.ini is in private/etc/php.ini.default
copy the file and call it php.ini

the default include path is usr/lib/php
(All these folders are hidden - use TinkerTool to reveal them)

<?php
$file
= fopen('textfile.txt', 'a', 1);
$text="\n Your text to write \n ".date('d')."-".date('m')."-".date('Y')."\n\n";
fwrite($file, $text);
fclose($file);
?>
up
-2
kzevian at cybercable dot net dot mx
9 years ago
I needed to append, but I needed to write on the file's beginning, and after some hours of effort this worked for me:

$file = "file.txt";
if (!file_exists("file.txt")) touch("file.txt");
$fh = fopen("file.txt", "r");
$fcontent = fread($fh, filesize("file.txt"));

$towrite = "$newcontent $fcontent";

$fh22 = fopen('file.txt', 'w+');
fwrite($fh2, $towrite);
fclose($fh);
fclose($fh2);
up
-2
bluevd at gmail dot com
9 years ago
Watch out for mistakes in writting a simple code for a hit counter:
<?php
$cont
=fopen('cont.txt','r');
$incr=fgets($cont);
//echo $incr;
$incr++;
fclose($cont);
$cont=fopen('cont.txt','a');
fwrite($cont,$incr);
fclose($cont);
?>

Why? notice the second fopen -> $cont=fopen('cont.txt','a');
it opens the file in writting mode (a). And when it ads the incremented
value ( $incr ) it ads it ALONG the old value... so opening the counter
page about 5 times will make your hits number look like this
012131214121312151.21312141213E+ .... you get the piont.
nasty, isn't it? REMEMBER to open the file with the 'w' mode (truncate
the file to 0). Doing this will clear the file content and it will make sure that
your counter works nice. This is the final code

<?php
$cont
=fopen('cont.txt','r');
$incr=fgets($cont);
//echo $incr;
$incr++;
fclose($cont);
$cont=fopen('cont.txt','w');
fwrite($cont,$incr);
fclose($cont);
?>

Notice that this work fine =)
XU (alias Iscu Andrei)
up
-2
Chris Blown
11 years ago
Don't forget to check fwrite returns for errors! Just because you successfully opened a file for write, doesn't always mean you can write to it. 

On some systems this can occur if the filesystem is full, you can still open the file and create the filesystem inode, but the fwrite will fail, resulting in a zero byte file.
up
-3
dominic at varspool dot com
5 months ago
Note that the optional $length argument is expected to be an int, and cannot be skipped by passing null.

That is, `fwrite($handle, $string, null)` is treated as `fwrite($handle, $string, 0)`, and will write zero bytes, not the whole string.
up
-3
sheyh
9 years ago
if you want to create quickly and without fopen use system, exec

system('echo "blahblah" > /path/file');
up
-7
michael at newbcity dot com
6 years ago
For my fellow newbies, if you test the sample script and want to have the .txt file created for you, you need to comment out the is_writable stuff, like this: 

<?php
$filename
= 'test.txt';
$somecontent = "Add this to the file\n";

// Let's make sure the file exists and is writable first.
//if (is_writable($filename)) {

// In our example we're opening $filename in append mode.
// The file pointer is at the bottom of the file hence
// that's where $somecontent will go when we fwrite() it.
if (!$handle = fopen($filename, 'a')) {
echo
"Cannot open file ($filename)";
exit;
}

// Write $somecontent to our opened file.
if (fwrite($handle, $somecontent) === FALSE) {
echo
"Cannot write to file ($filename)";
exit;
}

echo
"Success, wrote ($somecontent) to file ($filename)";

fclose($handle);

//} else {
//echo "The file $filename is not writable";
//}
?>
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