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fwrite

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

fwriteEscrita binary-safe em arquivos

Descrição

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

fwrite() grava o conteúdo de data no ponteiro de arquivo informado em stream.

Parâmetros

stream

Um resource de ponteiro do sistema de arquivos que normalmente é criado usando fopen().

data

A string a ser escrita.

length

Se length for um int, a escrita irá parar depois quelength forem escritos, ou o o fim de data for alcançado, o que ocorrer primeiro.

Valor Retornado

fwrite() retorna o número de bytes escritos, ou false em caso de falha.

Erros/Exceções

fwrite() emite um E_WARNING em caso falhas.

Registro de Alterações

Versão Descrição
8.0.0 length pode ser null.

Exemplos

Exemplo #1 Exemplo de fwrite()

<?php
$filename
= 'test.txt';
$somecontent = "Acrescente isso no arquivo\n";

// Vamos garantir que o arquivo existe e pode ser escrito
if (is_writable($filename)) {

// Nesse exemplo estamos abrindo o $filename em modo append.
// O ponteiro do arquivo estará no final do arquivo
// e portanto é aqui que $somecontent será posicionado pelo fwrite().
if (!$fp = fopen($filename, 'a')) {
echo
"Erro ao abrir o ($filename)";
exit;
}

// Escrever alguma coisa no arquivo.
if (fwrite($fp, $somecontent) === FALSE) {
echo
"Erro ao escrever no arquivo ($filename)";
exit;
}

echo
"Sucesso, escrito ($somecontent) no arquivo ($filename)";

fclose($fp);

} else {
echo
"O arquivo não permite escrita";
}
?>

Notas

Nota:

Escrever em um fluxo de rede pode acabar antes de toda a string ser transmitida. O retorno de fwrite() precisa ser inspecionado:

<?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;
}
?>

Nota:

Em sistemas que diferenciam entre arquivos binários e texto (por exemplo Windows) o arquivo tem que ser aberto com 'b' incluído no parâmetro 'mode' na fopen().

Nota:

Se o stream foi aberto com fopen() em modo de adição, escritas com fwrite() são atômicas (a não ser que o tamanho da data exceda o tamanho de bloco do sistema de arquivos, em algumas plataformas, e contanto que o arquivo esteja em um sistema de arquivos local). Sendo assim, não há necessidade de bloquear um recurso com flock() antes de chamar fwrite(); todos os dados serão escritos sem interrupção.

Nota:

Se escrever duas vezes no ponteiro do arquivo, então a informação será adicionado ao final do contéudo do arquivo:

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

// O conteúdo de 'data.txt' é 123, e não 23
?>

Veja Também

  • fread() - Leitura de arquivo segura para binário
  • fopen() - Abre um arquivo ou URL
  • fsockopen() - Abre uma conexão socket de domínio Unix ou de Internet
  • popen() - Abre um processo como ponteiro de arquivo
  • file_get_contents() - Lê todo o conteúdo de um arquivo para uma string
  • pack() - Empacota dados em uma string binária

adicione uma nota

Notas Enviadas por Usuários (em inglês) 10 notes

up
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;
}
?>
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
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
4
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
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
4
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
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));
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