When opening a file for reading and writing via fopen('file','a+') the file pointer should be at the end of the file. However ftell() returns int(0) even if the file is not empty. Also it seems that there is two pointers, first for reading and second for writing, because it acts differently on first operation (reading or writing).
Example:
<?php
$file = fopen('counter.txt', 'w');
fwrite($file, '123456789');
fclose($file);
$file = fopen('counter.txt', 'r');
echo ftell($file) . ' "' . fgets($file) . '" ' . ftell($file) . PHP_EOL;
fclose($file);
$file = fopen('counter.txt', 'a+');
echo ftell($file) . ' "' . fgets($file) . '" ' . ftell($file) . PHP_EOL;
fclose($file);
$file = fopen('counter.txt', 'r+');
fwrite($file, 'rr');
echo ftell($file) . ' "' . fgets($file) . '" ' . ftell($file) . PHP_EOL;
fclose($file);
$file = fopen('counter.txt', 'a+');
fwrite($file, 'aa');
echo ftell($file) . ' "' . fgets($file) . '" ' . ftell($file) . PHP_EOL;
fclose($file);
$file = fopen('counter.txt', 'r');
echo ftell($file) . ' "' . fgets($file) . '" ' . ftell($file) . PHP_EOL;
fclose($file);
?>
Result:
0 "123456789" 9
0 "123456789" 9
2 "3456789" 9
2 "" 2
0 "rr3456789aa" 11
ftell
(PHP 4, PHP 5, PHP 7, PHP 8)
ftell — ファイルの読み書き用ポインタの現在位置を返す
パラメータ
戻り値
stream が示すファイルポインタの位置、
すなわちファイル・ストリーム上のオフセットを整数値で返します。
エラーが起こった場合 false を返します。
注意: PHP の数値型は符号付整数であり、 多くのプラットフォームでは 32 ビットの整数を取るため、 ファイルシステム関数の中には 2GB より大きなファイルについては期待とは違う値を返すものがあります。
例
例1 ftell() の例
<?php
// ファイルをオープンし、データを読み込む
$fp = fopen("/etc/passwd", "r");
$data = fgets($fp, 12);
// どこにいるんだ ?
echo ftell($fp); // 11
fclose($fp);
?>
add a note
User Contributed Notes 8 notes
Mindaugas ¶
9 years ago
burninleo at gmx dot net ¶
15 years ago
When opening a file to append via fopen('file','ab') the file pointer should be at the end of the file. However ftell() returns int(0) even if the file is not empty and even after writing some text into the file.
d9k at ya dot ru ¶
2 years ago
Had to use
<?php
posix_isatty(STDIN) == false
?>
instead of
<?php
ftell(STDIN) !== false
?>
after upgrade from php 7 to 8 on ubuntu.
d9k at ya dot ru ¶
2 years ago
Had to use
<?php
posix_isatty(STDIN) == false
?>
instead of
<?php
ftell(STDIN) !== false
?>
after upgrade from php 7 to 8 on ubuntu.
mbirth at webwriters dot de ¶
19 years ago
Attention! If you open a file with the "text"-modifier (e.g. 'rt') and the file contains \r\n as line-endings, ftell() returns the position as if there were only \n as line-endings.
Example:
If the first line only contains 1 char followed by \r\n, the start of the second line should be position 3. (1char + \r + \n = 3 bytes) But ftell() will return 2 - ignoring one byte. If you call ftell() in line 3, the value will differ from the real value by 2 bytes. The error gets greater with every line.
(Watched this behavior in PHP 5.0.4 for Windows.)
BUT: fseek() works as expected - using the true byte values.
mweierophinney at gmail dot com ¶
19 years ago
Actually, ftell() gives more than an undefined result for append only streams; it gives the offset from the end of the file as defined before any data was appended. So if you open a file that had 3017 characters, and append 41 characters, and then execute ftell(), the value returned will be 41.
missilesilo at gmail dot com ¶
17 years ago
In response to php at michielvleugel dot com:
This does not seem to be the case with PHP 5.2.0 and FreeBSD 5.4.
#!/usr/local/bin/php
<?php
$tell = ftell(STDIN);
var_dump($tell);
?>
root@localhost:/home/david# echo Hello World | ./test.php
int(0)
root@localhost:/home/david# ./test.php
int(6629927)
When something is piped to the script, it returns an integer value of 0, however, it also returns an integer when nothing is piped to the script.
The code should be modified to this:
#!/usr/local/bin/php
<?php
$tell = ftell(STDIN);
if ($tell === 0)
echo "Something was piped: " . fread(STDIN,256) . "\n";
else
echo "Nothing was piped\n";
?>
And the result is:
root@localhost:/home/david# echo Hello World | ./test.php
Something was piped: Hello World
root@localhost:/home/david# ./test.php
Nothing was piped
php at michielvleugel dot com ¶
19 years ago
When trying to determine whether or not something was piped into a command line script, it is not smart to do a fgets(STDIN), because it will wait indefenitely if nothing is piped. Instead, I found ftell on STDIN to be very handy: it will return an integer of zero when something was piped, and nothing if nothing was piped to the script.
#!/usr/bin/php4 -q
<?
#following will hang if nothing is piped:
#$sometext = fgets(STDIN, 256)
$tell = ftell(STDIN);
if (is_integer($tell)==true)
{echo "Something was piped: ".fread(STDIN,256)."\n";}
else
{echo "Nothing was piped\n";}
?>
