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fwrite

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

fwriteバイナリセーフなファイル書き込み処理

説明

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

fwrite()dataの内容を streamが指しているファイル・ストリームに書き込みます。

パラメータ

stream

fopen() を使用して作成したファイルシステムポインタリソース。

data

書き込む文字列。

length

lengthパラメータが数値の場合、 lengthバイト数分の書き込みが完了したか、 dataが終わりに達したかのいずれか早い方の 事象により書き込みは中止されます。

戻り値

fwrite() は、 書き込んだバイト数を返します。 失敗した場合に false を返します

エラー / 例外

fwrite() は、 失敗した場合に E_WARNING を発生させます。

変更履歴

バージョン 説明
8.0.0 length は、nullable になりました。

例1 簡単な fwrite() の例

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

// ファイルが存在しかつ書き込み可能かどうか確認します
if (is_writable($filename)) {

// この例では$filenameを追加モードでオープンします。
// ファイルポインタはファイルの終端になりますので
// そこがfwrite()で$somecontentが追加される位置になります。
if (!$fp = fopen($filename, 'a')) {
echo
"Cannot open file ($filename)";
exit;
}

// オープンしたファイルに$somecontentを書き込みます
if (fwrite($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";
}
?>

注意

注意:

ネットワークストリームへの書き込みは、 すべての文字列を書き込み終える前に終了する可能性があります。 fwrite() の戻り値を確かめるようにしましょう。

<?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;
}
?>

注意:

(Windowsのように)バイナリとテキストファイルの形式が異なるシステムにおいては、ファイルをオープンする際に fopen()の mode パラメータに 'b' を指定する必要があります。

注意:

fopen() を使用して追記モードでオープンした stream の場合、 fwrite() はアトミックになります (ただし、一部のプラットフォームにおいて data がファイルシステムのブロックサイズを超えない場合、 そしてローカルファイルシステム上のファイルである場合に限ります)。 アトミックであるとは、つまり fwrite() をコールする前にリソースを flock() する必要がないということです。データの書き込みが中断されることはありません。

注意:

同じファイルポインタに 2 回書き込みを行うと、 データはファイルの末尾に追記されます。

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

// 'data.txt' の中身は 123 となります。23 ではありません!
?>

参考

  • fread() - バイナリセーフなファイルの読み込み
  • fopen() - ファイルまたは URL をオープンする
  • fsockopen() - インターネット接続もしくは Unix ドメインソケット接続をオープンする
  • popen() - プロセスへのファイルポインタをオープンする
  • file_get_contents() - ファイルの内容を全て文字列に読み込む
  • pack() - データをバイナリ文字列にパックする

add a note

User Contributed Notes 33 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
2
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
5
Anonymous
7 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
2
niklesh at example dot com
3 years ago
$handles can also be used to output in console like below example

fwrite(STDOUT, "Console Output");
up
4
Chris Blown
20 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
7 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
14 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
20 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
20 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
2 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
-2
Jon Haynes
12 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
9 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
-1
2184364 at gmail dot com
4 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
-3
chill at cuna dot org
19 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
18 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
20 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
15 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
-7
james at facepwn dot com
15 years ago
if (is_writable($filename)) {

Could also be

if (is_writable($filename) or die ("Can not write to ".$filename)) {
up
-7
Anonymous
9 years ago
Bad example!

The result of fwrite could be either FALSE or 0.

So it should be correctly:

if (false === fwrite($handle, $somecontent)) { ....
up
-4
David Spector
7 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
-7
sheyh
19 years ago
if you want to create quickly and without fopen use system, exec

system('echo "blahblah" > /path/file');
up
-8
oktavianus dot programmer at gmail dot com
14 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
-5
Will at EnigmaChannel dot com
19 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
-7
chad 0x40 herballure 0x2e com
16 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
-5
zaccraven at junk.com
17 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
-6
MKP Dev
18 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
-9
Andi
20 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
-8
kzevian at cybercable dot net dot mx
19 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
-11
elinor_hust at REMOVETHIS dot hotmail dot com
15 years ago
Remember to use double-quotes when outputting special characters such as \n or they come out literally.

...
up
-20
cutmaster at fearlesss dot com
17 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
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