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;
}
?>
fwrite
(PHP 4, PHP 5, PHP 7)
fwrite — Бинарно-безопасная запись в файл
Описание
fwrite
( resource
$handle
, string $string
[, int $length
] ) : int
fwrite() записывает содержимое string
в файловый поток handle.
Список параметров
-
handle -
Указатель (resource) на файл, обычно создаваемый с помощью функции fopen().
-
string -
Записываемая строка.
-
length -
Если передан аргумент
length, запись остановится после того, какlengthбайтов будут записаны или будет достигнут конец строкиstring, смотря что произойдёт раньше.Учтите, что если указан аргумент
length, то директива magic_quotes_runtime будет проигнорирована, и строкаstringне будет очищена от слешей.
Возвращаемые значения
fwrite() возвращает количество записанных байт
или FALSE в случае ошибки.
Примечания
Замечание:
Запись в сетевой поток может прекратиться до того, как будут записаны все данные. Это можно контролировать с помощью проверки возвращаемого значения функции fwrite():
<?php
function fwrite_stream($fp, $string) {
for ($written = 0; $written < strlen($string); $written += $fwrite) {
$fwrite = fwrite($fp, substr($string, $written));
if ($fwrite === false) {
return $written;
}
}
return $written;
}
?>
Замечание:
В системах, различающих двоичные и текстовые файлы (к примеру, Windows), файл должен быть открыт используя флаг 'b' в конце аргумента mode функции fopen().
Замечание:
Если дескриптор
handleбыл открыт функцией fopen() в режиме "добавление в конец", то вызовы fwrite() будут атомарными (за исключением случая, если размерstringпревысит размер блока файловой системы, на некоторых платформах, и пока файл хранится на локальной файловой системе). То есть нет необходимости блокировать ресурс с помощью flock() перед вызовом fwrite(), и все данные будут записаны без прерываний.
Замечание:
При повторной записи в файловый указатель, данные будут добавлены в конец содержимого файла:
<?php
$fp = fopen('data.txt', 'w');
fwrite($fp, '1');
fwrite($fp, '23');
fclose($fp);
// содержимое 'data.txt' теперь 123, а не 23!
?>
Примеры
Пример #1 Простой пример использования fwrite()
<?php
$filename = 'test.txt';
$somecontent = "Добавить это к файлу\n";
// Вначале давайте убедимся, что файл существует и доступен для записи.
if (is_writable($filename)) {
// В нашем примере мы открываем $filename в режиме "записи в конец".
// Таким образом, смещение установлено в конец файла и
// наш $somecontent допишется в конец при использовании fwrite().
if (!$handle = fopen($filename, 'a')) {
echo "Не могу открыть файл ($filename)";
exit;
}
// Записываем $somecontent в наш открытый файл.
if (fwrite($handle, $somecontent) === FALSE) {
echo "Не могу произвести запись в файл ($filename)";
exit;
}
echo "Ура! Записали ($somecontent) в файл ($filename)";
fclose($handle);
} else {
echo "Файл $filename недоступен для записи";
}
?>
Смотрите также
- fread() - Бинарно-безопасное чтение файла
- fopen() - Открывает файл или URL
- fsockopen() - Открывает соединение с интернет-сокетом или доменным сокетом Unix
- popen() - Открывает файловый указатель процесса
- file_get_contents() - Читает содержимое файла в строку
- pack() - Упаковать данные в бинарную строку
add a note
User Contributed Notes 30 notes
nate at frickenate dot com ¶
9 years ago
dharris dot nospam at removethispart dot drh dot net ¶
12 years ago
Some people say that when writing to a socket not all of the bytes requested to be written may be written. You may have to call fwrite again to write bytes that were not written the first time. (At least this is how the write() system call in UNIX works.)
This is helpful code (warning: not tested with multi-byte character sets)
function fwrite_with_retry($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");
Anonymous ¶
3 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;
}
?>
synnus at gmail dot com ¶
3 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;
}
?>
Chris Blown ¶
16 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.
php at biggerthanthebeatles dot com ¶
16 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.
chedong at hotmail dot com ¶
16 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));
Anonymous ¶
10 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.
2184364 at gmail dot com ¶
4 months 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);
chill at cuna dot org ¶
15 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";
}
Jon Haynes ¶
8 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.
Anonymous ¶
5 years ago
Bad example!
The result of fwrite could be either FALSE or 0.
So it should be correctly:
if (false === fwrite($handle, $somecontent)) { ....
dominic at varspool dot com ¶
6 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, $string, 0)`, and will write zero bytes, not the whole string.
james at facepwn dot com ¶
11 years ago
if (is_writable($filename)) {
Could also be
if (is_writable($filename) or die ("Can not write to ".$filename)) {
kzevian at cybercable dot net dot mx ¶
15 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);
Jake Roberts ¶
16 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($fh)) ) die "Error Reading";
Thus it will be successful on reading zero bytes but detect and error returned as FALSE.
qrworld.net ¶
5 years ago
Here you have a function found on the website http://softontherocks.blogspot.com/2014/11/funcion-para-escribir-en-un-fichero-log.html with an example of how to make a log file.
The function is this:
function writeLog($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
}
sheyh ¶
15 years ago
if you want to create quickly and without fopen use system, exec
system('echo "blahblah" > /path/file');
oktavianus dot programmer at gmail dot com ¶
10 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
bluevd at gmail dot com ¶
15 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)
chad 0x40 herballure 0x2e com ¶
12 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.
Andi ¶
16 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.
Will at EnigmaChannel dot com ¶
14 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);
?>
ceo at l-i-e dot com ¶
11 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
zaccraven at junk.com ¶
13 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.
james at nicolson dot biz ¶
14 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;
}
?>
cutmaster at fearlesss dot com ¶
12 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
elinor_hust at REMOVETHIS dot hotmail dot com ¶
11 years ago
Remember to use double-quotes when outputting special characters such as \n or they come out literally.
...
MKP Dev ¶
14 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 ($handle); // Done
?>
David Spector ¶
3 years ago
This may save you time: note that neither "binary-safe file write" nor the use of b mode in fopen mean that fwrite can write binary. It can only write strings (or a single character). For example, attempting to write the byte 0x1 using fwrite results in writing the byte value 0x31.
If you wish to write binary values (bits, bytes, integers, etc.), use a statement like fprintf($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).
