ftell

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

    ftell — 返回文件指针读/写的位置

    说明

    ftell(resource $stream): int|false

    返回由 stream 指定的文件指针的位置，也就是文件流中的偏移量。

    参数

    stream

    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。

    返回值

    以整数形式返回由 stream 引用的文件指针的位置，即文件流中的偏移量。

    如果出错，返回 false。

    注意: 因为 PHP 的整数类型是有符号整型而且很多平台使用 32 位整型，对 2GB 以上的文件，一些文件系统函数可能返回无法预期的结果。

    示例

    示例 #1 ftell() 例子

    <?php

    // opens a file and read some data
    $fp = fopen("/etc/passwd", "r");
    $data = fgets($fp, 12);

    // where are we ?
    echo ftell($fp); // 11

    fclose($fp);

    ?>

    参见

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    用户贡献的备注 8 notes

    up
    7
    Mindaugas
    9 years ago
    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
    up
    2
    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.
    up
    0
    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.
    up
    0
    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.
    up
    0
    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.
    up
    0
    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.
    up
    -2
    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
    up
    -2
    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";}

    ?>
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