fwrite

(PHP 4, PHP 5, PHP 7, PHP 8)

fwrite — Binary-safe file write

Descripción

fwrite(resource $stream, string $data, ?int $length = null): int|false

fwrite() writes the contents of data to the file stream pointed to by stream.

Parámetros

stream: Resource que apunta a un fichero del sitema que normalmente es creado usando fopen().
data: The string that is to be written.
length: If length is an int, writing will stop after length bytes have been written or the end of data is reached, whichever comes first.

Valores devueltos

fwrite() returns the number of bytes written, o false en caso de error.

Errores/Excepciones

fwrite() raises E_WARNING on failure.

Historial de cambios

Versión	Descripción
8.0.0	`length` is nullable now.

Ejemplos

Ejemplo #1 A simple fwrite() example

<?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 $somecontent will go when we fwrite() it.
    if (!$fp = fopen($filename, 'a')) {
         echo "Cannot open file ($filename)";
         exit;
    }

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

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

    fclose($fp);

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

Notas

Nota:
Writing to a network stream may end before the whole string is written. Return value of fwrite() may be checked:

<?php 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; } ?>

Nota:
On systems which differentiate between binary and text files (i.e. Windows) the file must be opened with 'b' included in fopen() mode parameter.

Nota:
If stream was fopen()ed in append mode, fwrite()s are atomic (unless the size of data exceeds the filesystem's block size, on some platforms, and as long as the file is on a local filesystem). That is, there is no need to flock() a resource before calling fwrite(); all of the data will be written without interruption.

Nota:
If writing twice to the file pointer, then the data will be appended to the end of the file content:

<?php $fp = fopen('data.txt', 'w'); fwrite($fp, '1'); fwrite($fp, '23'); fclose($fp); // the content of 'data.txt' is now 123 and not 23! ?>

Ver también

fread() - Lectura de un fichero en modo binario seguro
fopen() - Abre un fichero o un 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 completo a una cadena
pack() - Empaqueta información a una cadena binaria

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User Contributed Notes 10 notes

down

109

nate at frickenate dot com ¶

14 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;

}

?>

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divinity76 at gmail dot com ¶

3 years ago

if you need a function that writes all data, maybe try

<?php

    /**
     * writes all data or throws
     *
     * @param mixed $handle
     * @param string $data
     * @throws \RuntimeException when fwrite returned <1 but still more data to write
     * @return void
     */
    /*private static*/ function fwrite_all($handle, string $data): void
    {
        $original_len = strlen($data);
        if ($original_len > 0) {
            $len = $original_len;
            $written_total = 0;
            for (;;) {
                $written_now = fwrite($handle, $data);
                if ($written_now === $len) {
                    return;
                }
                if ($written_now < 1) {
                    throw new \RuntimeException("could only write {$written_total}/{$original_len} bytes!");
                }
                $written_total += $written_now;
                $data = substr($data, $written_now);
                $len -= $written_now;
                // assert($len > 0);
                // assert($len === strlen($data));
            }
        }
    }

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niklesh at example dot com ¶

4 years ago

$handles can also be used to output in console like below example

fwrite(STDOUT, "Console Output");

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Chris Blown ¶

21 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.

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Anonymous ¶

8 years ago

// you want copy dummy file or send dummy file 
// it is possible to send a file larger than 4GB and write without FSEEK used is limited by PHP_INT_MAX. it works on a system 32-bit or 64-bit
// fwrite and fread non pas de limite de position du pointeur 

<?php

$gfz =  filesize_dir("d:\\starwars.mkv"); // 11,5GB
echo 'Z:',$gfz,PHP_EOL;

$fz = fopen('d:\\test2.mkv', 'wb'); 
$fp = fopen('d:\\starwars.mkv', 'rb');
echo PHP_EOL;
$a = (float) 0;
while(($l=fread($fp, 65536))) { 
    fwrite($fz, $l);
    if(($a+=65536)%5) echo "\r", '>', $a, ' : ' , $gfz;
}

fclose($fp);
fclose($fz);

// test2.mkv' is 11,5GB

    function filesize_dir($file) {
        exec('dir ' . $file, $inf);
        $size_raw = $inf[6];
        $size_exp = explode(" ",$size_raw);
        $size_ext = $size_exp[19];
        $size_int = (float) str_replace(chr(255), '', $size_ext);
        return $size_int;
    }
?>

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dharris dot nospam at removethispart dot drh dot net ¶

16 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");

down

synnus at gmail dot com ¶

8 years ago

// you want copy dummy file or send dummy file 
// it is possible to send a file larger than 4GB and write without FSEEK used is limited by PHP_INT_MAX. it works on a system 32-bit or 64-bit
// fwrite and fread non pas de limite de position du pointeur 

<?php

$gfz =  filesize_dir("d:\\starwars.mkv"); // 11,5GB
echo 'Z:',$gfz,PHP_EOL;

$fz = fopen('d:\\test2.mkv', 'wb'); 
$fp = fopen('d:\\starwars.mkv', 'rb');
echo PHP_EOL;
$a = (float) 0;
while(($l=fread($fp, 65536))) { 
    fwrite($fz, $l);
    if(($a+=65536)%5) echo "\r", '>', $a, ' : ' , $gfz;
}

fclose($fp);
fclose($fz);

// test2.mkv' is 11,5GB

    function filesize_dir($file) {
        exec('dir ' . $file, $inf);
        $size_raw = $inf[6];
        $size_exp = explode(" ",$size_raw);
        $size_ext = $size_exp[19];
        $size_int = (float) str_replace(chr(255), '', $size_ext);
        return $size_int;
    }
?>

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php at biggerthanthebeatles dot com ¶

21 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.

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Anonymous ¶

15 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.

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chedong at hotmail dot com ¶

21 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));

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