Filesystem 函数
在线手册：中文 英文
PHP手册

ftell

(PHP 4, PHP 5)

ftell — 返回文件指针读/写的位置

说明

int ftell ( resource $handle )

返回由 handle 指定的文件指针的位置，也就是文件流中的偏移量。

如果出错，返回 FALSE。

文件指针必须是有效的，且必须指向一个通过 fopen() 或 popen() 成功打开的文件。在附加模式（加参数 "a" 打开文件）中 ftell() 会返回未定义错误。

Example #1 ftell() 例子

<?php

// 打开文件并读些数据
$fp = fopen("/etc/passwd", "r");
$data = fgets($fp, 12);

// 现在指针到哪里了？
echo ftell($fp); // 11

fclose($fp);

?>

参见 fopen()，popen()，fseek() 和 rewind()。

Filesystem 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 返回文件指针读/写的位置

用户评论:

burninleo at gmx dot net (07-Sep-2009 09:38)

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.

missilesilo at gmail dot com (27-Feb-2007 11:02)

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

mbirth at webwriters dot de (21-Oct-2005 07:09)

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 (21-Jun-2005 06:00)

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.

php at michielvleugel dot com (01-Jun-2005 11:19)

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";}

?>