fwrite
(PHP 4, PHP 5, PHP 7, PHP 8)
Binary-safe file write
Description
fwrite() writes the contents of data to the file stream pointed to by stream.
Parameters
streamPointer
dataThe string that is to be written.
lengthIf
lengthis an Integer, writing will stop afterlengthbytes have been written or the end ofdatais reached, whichever comes first.
Return Values
fwrite() returns the number of bytes written, Falseforfailure.
Errors/Exceptions
fwrite() raises E_WARNING on failure.
Changelog
| Version | Description |
|---|---|
| 8.0.0 | length is nullable now. |
Examples
A simple fwrite() example
<?php
$filename = 'test.txt';
$somecontent = "Add this to the file\n";
// Let's make sure the file exists and is writable first.
if (is_writable($filename)) {
// In our example we're opening $filename in append mode.
// The file pointer is at the bottom of the file hence
// that's where $somecontent will go when we fwrite() it.
if (!$fp = fopen($filename, 'a')) {
echo "Cannot open file ($filename)";
exit;
}
// Write $somecontent to our opened file.
if (fwrite($fp, $somecontent) === FALSE) {
echo "Cannot write to file ($filename)";
exit;
}
echo "Success, wrote ($somecontent) to file ($filename)";
fclose($fp);
} else {
echo "The file $filename is not writable";
}
?>Notes
Writing to a network stream may end before the whole string is written. Return value of fwrite() may be checked:
<?php
function fwrite_stream($fp, $string) {
for ($written = 0; $written < strlen($string); $written += $fwrite) {
$fwrite = fwrite($fp, substr($string, $written));
if ($fwrite === false) {
return $written;
}
}
return $written;
}
?>On systems which differentiate between binary and text files (i.e. Windows) the file must be opened with 'b' included in fopen() mode parameter.
If stream was fopen()ed in append mode, fwrite()s are atomic (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). That is, there is no need to flock() a resource before calling fwrite(); all of the data will be written without interruption.
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!
?>