fseek

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

fseek — Seeks on a file pointer

Description

fseek(resource $stream, int $offset, int $whence = SEEK_SET): int

Sets the file position indicator for the file referenced by stream. The new position, measured in bytes from the beginning of the file, is obtained by adding offset to the position specified by whence.

In general, it is allowed to seek past the end-of-file; if data is then written, reads in any unwritten region between the end-of-file and the sought position will yield bytes with value 0. However, certain streams may not support this behavior, especially when they have an underlying fixed size storage.

Parameters

stream

A file system pointer resource that is typically created using fopen().

offset

The offset.

To move to a position before the end-of-file, you need to pass a negative value in offset and set whence to SEEK_END.

whence

whence values are:

  • SEEK_SET - Set position equal to offset bytes.
  • SEEK_CUR - Set position to current location plus offset.
  • SEEK_END - Set position to end-of-file plus offset.

Return Values

Upon success, returns 0; otherwise, returns -1.

Examples

Example #1 fseek() example

<?php

$fp = fopen('somefile.txt', 'r');

// read some data
$data = fgets($fp, 4096);

// move back to the beginning of the file
// same as rewind($fp);
fseek($fp, 0);

?>

Notes

Note:

If you have opened the file in append (a or a+) mode, any data you write to the file will always be appended, regardless of the file position, and the result of calling fseek() will be undefined.

Note:

Not all streams support seeking. For those that do not support seeking, forward seeking from the current position is accomplished by reading and discarding data; other forms of seeking will fail.

See Also

  • ftell() - Returns the current position of the file read/write pointer
  • rewind() - Rewind the position of a file pointer