Re: unpack on offsets in binary data in variable?

Markus Fischer wrote: > Hi, > > I'm searching for an efficient way to use unpack on binary data within a > variable (php 5.1.something). In the past I was doing > > fopen > fseek > unpack( fread(...) > fseek > etc. > > Now this time I need to do the same, but I don't have an actual file: my > data is only in a variable and I don't want to operate on a file but the > variable within. > > I was thinking about using substr() and passing the small chunks of data > I need to the unpack() function. > > Question: does this work without problems on arbitrary binary, maybe > containing zero-byte values reliable? Hi Markus, This does work fine, but beware of strange behavior with unpack() when using unsigned types V, N, or L. I recently was bitten by different behavior on 32-bit and 64-bit OSes unpacking a large unsigned integer. If you need unsigned, use sprintf("%u", $whatever) to get the actual integer. substr() works nicely on strings for unpack(), see how PHP_Archive uses it in http://cvs.php.net/viewvc.cgi/pear/PHP_Archive/Archive.php . If you are writing for forward compatibility with PHP 6's unicode and plan to accept input from a variety of sources, you may want to cast the string to binary type. Greg