fwrite

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

fwrite — 写入文件（可安全用于二进制文件）

说明

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

fwrite() 把 data 的内容写入文件指针 stream 处。

参数

stream: 文件系统指针，是典型地由 fopen() 创建的 resource(资源)。
data: 要写入的字符串。
length: 如果 length 是 int，当写入了 length 个字节或者写完了 string 以后，写入就会停止，看先碰到哪种情况。

返回值

fwrite() 返回写入的字符数，或者在失败时返回 false。

错误／异常

fwrite() 失败时会引发 E_WARNING。

更新日志

版本	说明
8.0.0	现在 `length` 可以为 null。

示例

示例 #1 简单的 fwrite() 示例

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

// 首先确认文件存在且可写。
if (is_writable($filename)) {

    // 在示例中，使用追加模式打开 $filename。
    // 文件指针应该在文件的末尾，
    // 那就是使用 fwrite() 写入 $somecontent 的地方。
    if (!$fp = fopen($filename, 'a')) {
         echo "Cannot open file ($filename)";
         exit;
    }

    // 将 $somecontent 写入到打开的文件。
    if (fwrite($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";
}
?>

注释

注意:
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; } ?>

注意:
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'。

注意:
如果 stream 是 fopen() 追加模式，fwrite() 是原子操作（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）。也就是说，在调用 fwrite() 之前不需要 flock() 资源；所有的数据都将会不间断写入。

注意:
如果向文件指针写入两次，然后数据将追加到文件内容的末尾：

<?php $fp = fopen('data.txt', 'w'); fwrite($fp, '1'); fwrite($fp, '23'); fclose($fp); // “data.txt”的内容是 123 而不是 23！ ?>

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 Internet 或者 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
pack() - 将数据打包成二进制字符串

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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;

}

?>

down

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");

down

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.

down

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;
    }
?>

down

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;
    }
?>

down

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.

down

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));