PHP Australia Conference 2015

fwrite

(PHP 4, PHP 5)

fwriteEscritura de un archivo en modo binario seguro

Descripción

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

fwrite() escribe el contenido de string al flujo de archivo apuntado por handle.

Parámetros

handle

Resource que apunta a un fichero del sitema que normalmente es creado usando fopen().

string

La cadena que va a ser escrita.

length

Si se da el argumento length, la escritura se detendrá después de que length bytes hayan sido escritos o se alcance el final de string, lo que suceda primero.

Observe que si el argumento length se da, la opción de configuración magic_quotes_runtime será ignorada y no se eliminarán las barras de string.

Valores devueltos

fwrite() devuelve el número de bytes escritos, o FALSE si se produjo un error.

Notas

Nota:

Escribir en un flujo de red puede terminar antes de que se haya escrito la cadena completa. El valor devuelto por fwrite() se puede verificar:

<?php
function flujo_fwrite($fp$cadena) {
    for (
$escrito 0$escrito strlen($cadena); $escrito += $fwrite) {
        
$fwrite fwrite($fpsubstr($cadena$escrito));
        if (
$fwrite === false) {
            return 
$escrito;
        }
    }
    return 
$escrito;
}
?>

Nota:

En sistemas en los que se diferencia entre archivos binarios y de texto (esto es, Windows) el archivo debe ser abierto con 'b' incluida en el parámetro modo de fopen().

Nota:

Si handle fue abierto por fopen() en modo de adición, las escrituras de fwrite() son atómicas (a menos que el tamaño de string exceda el tamaño de bloque del sistema de archivos, en algunas plataformas, siempre que el archivo esté en un sistema de archivos local). Es decir, no hay necesidad de bloquear un recurso con flock() antes de llamar a fwrite(); toda la información será escrita sin interrupciones.

Nota:

Si se escribe dos veces sobre el puntero al archivo la información será añadida al final del contenido del archivo:

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

// ¡el contenido de 'data.txt' ahora es 123 y no 23!
?>

Ejemplos

Ejemplo #1 Un ejemplo sencillo de fwrite()

<?php
$nombre_archivo 
'prueba.txt';
$contenido "Añade esto al archivo\n";

// Primero vamos a asegurarnos de que el archivo existe y es escribible.
if (is_writable($nombre_archivo)) {

    
// En nuestro ejemplo estamos abriendo $nombre_archivo en modo de adición.
    // El puntero al archivo está al final del archivo
    // donde irá $contenido cuando usemos fwrite() sobre él.
    
if (!$gestor fopen($nombre_archivo'a')) {
         echo 
"No se puede abrir el archivo ($nombre_archivo)";
         exit;
    }

    
// Escribir $contenido a nuestro archivo abierto.
    
if (fwrite($gestor$contenido) === FALSE) {
        echo 
"No se puede escribir en el archivo ($nombre_archivo)";
        exit;
    }

    echo 
"Éxito, se escribió ($contenido) en el archivo ($nombre_archivo)";

    
fclose($gestor);

} else {
    echo 
"El archivo $nombre_archivo no es escribible";
}
?>

Ver también

  • fread() - Lectura de un fichero en modo binario seguro
  • fopen() - Abre un fichero o una URL
  • fsockopen() - Abre una conexión vía sockets a Internet o a un dominio Unix
  • popen() - Abre un proceso de un puntero a un fichero
  • file_get_contents() - Transmite un fichero entero a una cadena

add a note add a note

User Contributed Notes 27 notes

up
17
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
9
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
11 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
0
Anonymous
21 days ago
Bad example!

The result of fwrite could be either FALSE or 0.

So it should be correctly:

if (false === fwrite($handle, $somecontent)) { ....
up
0
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
-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
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
-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
-2
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
-2
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
bahatest at ifrance doc com
9 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
-3
chad 0x40 herballure 0x2e com
7 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
zaccraven at junk.com
8 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
-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
-5
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
-3
dominic at varspool dot com
7 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
-5
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
-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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