php教程

fwrite

(PHP 4, PHP 5, PHP 7)

fwrite — 写入文件（可安全用于二进制文件）

说明

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

fwrite() 把 string 的内容写入 文件指针 handle 处。

参数

handle

文件系统指针，是典型地由 fopen() 创建的 resource(资源)。

string

The string that is to be written.

length

如果指定了 length，当写入了 length 个字节或者写完了 string 以后，写入就会停止，视乎先碰到哪种情况。

注意如果给出了 length 参数，则 magic_quotes_runtime 配置选项将被忽略，而 string 中的斜线将不会被抽去。

返回值

fwrite() 返回写入的字符数，出现错误时则返回 FALSE 。

注释

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:

在区分二进制文件和文本文件的系统上（如 Windows） 打开文件时，fopen() 函数的 mode 参数要加上 'b'。

Note:

If handle was fopen()ed in append mode, fwrite()s are atomic (unless the size of string 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!
?>

范例

Example #1 一个简单的 fwrite() 例子

<?php
$filename = 'test.txt';
$somecontent = "添加这些文字到文件\n";

// 首先我们要确定文件存在并且可写。
if (is_writable($filename)) {

    // 在这个例子里，我们将使用添加模式打开$filename，
    // 因此，文件指针将会在文件的末尾，
    // 那就是当我们使用fwrite()的时候，$somecontent将要写入的地方。
    if (!$handle = fopen($filename, 'a')) {
         echo "不能打开文件 $filename";
         exit;
    }

    // 将$somecontent写入到我们打开的文件中。
    if (fwrite($handle, $somecontent) === FALSE) {
        echo "不能写入到文件 $filename";
        exit;
    }

    echo "成功地将 $somecontent 写入到文件$filename";

    fclose($handle);

} else {
    echo "文件 $filename 不可写";
}
?>

参见

  • fread() - 读取文件（可安全用于二进制文件）
  • fopen() - 打开文件或者 URL
  • fsockopen() - 打开一个网络连接或者一个Unix套接字连接
  • popen() - 打开进程文件指针
  • file_get_contents() - 将整个文件读入一个字符串

User Contributed Notes

David Spector 27-Jul-2016 02:01
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).
synnus at gmail dot com 02-Apr-2016 05:49
// 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;
    }
?>
Anonymous 02-Apr-2016 05:48
// 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;
    }
?>
qrworld.net 11-Nov-2014 03:06
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
}
Anonymous 09-Sep-2014 02:56
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 04-Feb-2014 04:49
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.
Jon Haynes 01-Apr-2011 02:48
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.
nate at frickenate dot com 24-Mar-2010 09:51
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;
}
?>
oktavianus dot programmer at gmail dot com 03-Jun-2009 08:51
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
Anonymous 15-May-2009 09:36
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.
ceo at l-i-e dot com 10-Nov-2008 03:07
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
james at facepwn dot com 09-Oct-2008 05:25
if (is_writable($filename)) {

Could also be

if (is_writable($filename) or die ("Can not write to ".$filename)) {
elinor_hust at REMOVETHIS dot hotmail dot com 01-Apr-2008 05:26
Remember to use double-quotes when outputting special characters such as \n or they come out literally.

...
dharris dot nospam at removethispart dot drh dot net 20-Feb-2008 10:47
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");
chad 0x40 herballure 0x2e com 05-Sep-2007 10:13
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.
cutmaster at fearlesss dot com 09-Mar-2007 03:09
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 éèà?");
$fh=fopen('test.xml',"w");
fwrite($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 éèà?";
$fh=fopen('test.xml',"w");
fwrite($fh,utf8_encode($myString));
fclose($fh);
?>
Hope this will help
zaccraven at junk.com 11-Sep-2006 12:08
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 06-Jul-2005 08:09
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;
}     
?>
MKP Dev 12-May-2005 05:25
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
?>
Will at EnigmaChannel dot com 25-Mar-2005 06:24
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);
?>
sheyh 09-Feb-2005 09:55
if you want to create quickly and without fopen use system, exec

system('echo "blahblah" > /path/file');
kzevian at cybercable dot net dot mx 03-Feb-2005 11:27
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);
bluevd at gmail dot com 22-Dec-2004 09:56
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)
chill at cuna dot org 26-Oct-2004 03:32
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";
}
php at biggerthanthebeatles dot com 21-Aug-2003 03:04
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.
Andi 17-Jul-2003 02:32
[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.
chedong at hotmail dot com 20-Jun-2003 02:36
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));
Jake Roberts 04-Jun-2003 11:35
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.
Chris Blown 19-May-2003 03:12
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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