PHP 8.4.0 RC4 available for testing

fwrite

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

fwriteBinary-safe file write

Description

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

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

Parameters

stream

A file system pointer resource that is typically created using 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.

Return Values

fwrite() returns the number of bytes written, or false on failure.

Errors/Exceptions

fwrite() raises E_WARNING on failure.

Changelog

Version Description
8.0.0 length is nullable now.

Examples

Example #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";
}
?>

Notes

Note:

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;
}
?>

Note:

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

Note:

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.

Note:

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!
?>

See Also

add a note

User Contributed Notes 22 notes

up
107
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;
}
?>
up
3
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));
}
}
}
up
3
niklesh at example dot com
4 years ago
$handles can also be used to output in console like below example

fwrite(STDOUT, "Console Output");
up
5
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;
}
?>
up
5
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.
up
5
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");
up
2
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;
}
?>
up
3
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.
up
2
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));
up
3
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.
up
0
synnus at gmail dot com
3 years ago
<?php
/*
Write to offset with positive offset

PHP_INT_MIN / PHP_INT_MAX 32-bit PHP: -2,147,483,648 to +2,147,483,647
PHP_INT_MIN / PHP_INT_MAX 64-bit PHP: -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807

File_writing 32bit 0 -> 4 294 967 295
File_writing 64bit 0 -> 18 446 744 073 709 551 615

$handel = fopen( myfilname );
$t_f_max is max file size in BYTE ex: 19998
$offset is position in offset BYTE ex : 19995
$bin your binary data you want write

Work in 32bit and 64bit
*/

function File_writing($handel,$t_f_max,$offset,$bin) {
(
$offset > PHP_INT_MAX) ? fseek($handel,-($t_f_max-$offset),SEEK_END) : fseek($handel,$offset,SEEK_SET);
fwrite($handel,$bin);
return
$offset;
}

?>
up
0
2184364 at gmail dot com
5 years ago
//fwrite writes over, i.e. this example (win) may be misleading:

$file = 'e:/1.txt';

file_put_contents($file, 'hello'.chr(1).'0df6ac'.chr(0));

$fp = fopen($file, 'r+b');

$str = fread($fp, filesize($file));

$str = strtr($str, [chr(0)=>'']);
echo $str.PHP_EOL;//hello0df6ac

fseek($fp, 0);//указатель в начало
fwrite($fp, $str);

fclose($fp);

//add ftruncate ($ fp, 0);
//this will overwrite the file:

file_put_contents($file, 'hello'.chr(1).'0df6ac'.chr(0));

$fp = fopen($file, 'r+b');

$str = fread($fp, filesize($file));

$str = strtr($str, [chr(0)=>'']);
echo $str.PHP_EOL;//hello0df6ac

ftruncate ($ fp, 0);
fseek($fp, 0);//указатель в начало
fwrite($fp, $str);

fclose($fp);
up
-1
Jon Haynes
13 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
-1
qrworld.net
10 years ago
Here you have a function found on the website http://softontherocks.blogspot.com/2014/11/funcion-para-escribir-en-un-fichero-log.html with an example of how to make a log file.

The function is this:

function writeLog($data) {
list($usec, $sec) = explode(' ', microtime());
$datetime = strftime("%Y%m%d %H:%M:%S",time());
$msg = "$datetime'". sprintf("%06s",intval($usec*1000000)).": $data";
$save_path = 'foo.txt';
$fp = @fopen($save_path, 'a'); // open or create the file for writing and append info
fputs($fp, "$msg\n"); // write the data in the opened file
fclose($fp); // close the file
}
up
-2
chill at cuna dot org
20 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
-4
dominic at varspool dot com
10 years 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
james at nicolson dot biz
19 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
-5
Jake Roberts
21 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
-5
bluevd at gmail dot com
19 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
-4
ceo at l-i-e dot com
16 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
-4
David Spector
8 years ago
This may save you time: note that neither "binary-safe file write" nor the use of b mode in fopen mean that fwrite can write binary. It can only write strings (or a single character). For example, attempting to write the byte 0x1 using fwrite results in writing the byte value 0x31.

If you wish to write binary values (bits, bytes, integers, etc.), use a statement like fprintf($Res, "%c", 0x1); . This statement will write a byte to the current offset in the file without converting it to a character (in this case, it will write 0x1).
up
-5
zaccraven at junk.com
18 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.
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