PHP: gzseek - Manual

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

gzseek — Seek on a gz-file pointer

Description

If the file is opened for reading, this function is emulated but can be extremely slow. If the file is opened for writing, only forward seeks are supported; gzseek() then compresses a sequence of zeroes up to the new starting position.

Parameters

stream

The gz-file pointer. It must be valid, and must point to a file successfully opened by gzopen().

offset

The seeked offset.

whence

whence values are:

• SEEK_SET - Set position equal to offset bytes.
• SEEK_CUR - Set position to current location plus offset.

If whence is not specified, it is assumed to be SEEK_SET.

Return Values

Upon success, returns 0; otherwise, returns -1. Note that seeking past EOF is not considered an error.

Examples

<?php
$gz = gzopen('somefile.gz', 'r');
gzseek($gz,2);
echo gzgetc($gz);
gzclose($gz);
?>

See Also

• gztell() - Tell gz-file pointer read/write position
• gzrewind() - Rewind the position of a gz-file pointer

liuhaifeng at example dot com ¶

13 years ago

Since seek after the end is not considered an error, I doubt that "while (gzseek ($fh, $eof) == 0) $eof += $d;" will get into infinite loop.

dperham at wgate dot com ¶

21 years ago

PHP/4.3.9
contrary to the notes, gzseek() returns -1 if I try to seek past the end of the file.  here is a function that will return the last seekable position, and put the file pointer there.

/** sets the file pointer at the end of the file
 *  and returns the number of bytes in the file.
 */
function gzend($fh)
{
   $d   = 1<<14;
   $eof = $d;
   while ( gzseek($fh, $eof) == 0 ) $eof += $d;
   while ( $d > 1 )
   {
      $d >>= 1;
      $eof += $d * (gzseek($fh, $eof)? -1 : 1);
   }
   return $eof;
}