PHP fseek() equivalent for variables?

Question

Hi,

What I need is an equivalent for PHP's fseek() function. The function works on files, but I have a variable that contains binary data and I want to work on it. I know I could use substr(), but that would be lame - it's used for strings, not for binary data. Also, creating a file and then using fseek() is not what I am looking for either.

Maybe something constructed with streams?

EDIT: Okay, I'm almost there:

$data = fopen('data://application/binary;binary,'.$bin,'rb');

Warning: failed to open stream: rfc2397: illegal parameter

Answer 1

Kai:

You have almost answered yourself here. Streams are the answer. The following manual entry will be enlightening: http://us.php.net/manual/en/wrappers.data.php

It essentially allows you to pass arbitrary data to PHP's file handling functions such as fopen (and thus fseek).

Then you could do something like:

<?php

$data = fopen('data://mime/type;encoding,' . $binaryData);

fseek($data, 128);
?>

Answer 2

fseek on data in a variable doesn't make sense. fseek just positions the file handle to the specified offset, so the next fread call starts reading from that offset. There is no equivalent of fread for strings.

Whats wrong with substr()?

With a file you would do:

$f = fopen(...)
fseek($f, offset)
$x = fread($f, len)

with substr:

$x = substr($var, offset, len)