gzseek()

(PHP 4, PHP 5, PHP 7)

Seek on a gz-file pointer

说明

gzseek(resource $zp,int $offset[,int $whence= SEEK_SET]): int

Sets the file position indicator for the given file pointer to the given offset byte into the file stream. Equivalent to calling(in C)gzseek(zp, offset, SEEK_SET).

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.

参数

$zp

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

$offset

The seeked offset.

$whence

$whencevalues are:

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

If$whenceis not specified, it is assumed to be SEEK_SET.

返回值

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

范例

gzseek() example

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

参见

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

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.

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;
}