fflush

(PHP 4 >= 4.0.1, PHP 5, PHP 7)

fflush — Flushes the output to a file

Description

bool fflush ( resource $handle )

This function forces a write of all buffered output to the resource pointed to by the file handle.

Parameters

handle: The file pointer must be valid, and must point to a file successfully opened by fopen() or fsockopen() (and not yet closed by fclose()).

Return Values

Returns TRUE on success or FALSE on failure.

Examples

Example #1 File write example using fflush()


<?php
$filename = 'bar.txt';

$file = fopen($filename, 'r+');
rewind($file);
fwrite($file, 'Foo');
fflush($file);
ftruncate($file, ftell($file));
fclose($file);
?>

User Contributed Notes

jzho327 at cse dot unsw dot edu dot au

13 years ago


Sorry, the note I previously added regarding fflush() has a bug!

when you read file by calling 
$fp = fopen("myfile", "a+");

and you wish to read the content, you have to call 
rewind($fp) before you attemp to read it. (Silly me) Or else if you tried something like
$fp = fopen("myfile", "a+");
$content = fread($fp);

// show that content is in fact null
if ($content == NULL)
 print "but it must be first put to rewind<br>\n";

will result

but it must be first put to rewind.
[new line]

in fact, if you are not careful (like me), and you opened it with
$fp = fopen("myfile", "r+");
$content = fread($fp);
..
// do something with content
..
then you tried to again
$content = fread($fp);
without rewind, you'd get NULL again. This sounds trivial, but if you work with several file resources, with freads and fopens everywhere, you can get easily lost. So becareful.

oryan at zareste dot com

10 years ago


Just a note that fflush takes care of the cache already, at least on my server.  Using clearstatcache before reading a previously written file also worked, but lagged the output time much more noticeably (by two or three seconds), probably due to excess cache erasing beyond files.