RE: [PHP] Can someone explain this?

On 08 June 2004 19:00, René Fournier wrote: > OK, that makes sense. But here's the problem: I receive binary data > from SuperSPARC (big-endian), which I need to unpack according to > certain documented type definitions. For example, let's say that $msg > has the value "3961595508" and is packed as an unsigned long integer > (on the remote SPARC). But when I receive it, and unpack it... > > $unpacked = unpack('Nval', $msg); // N for unsigned long integer, > big-endian (SPARC) echo $unpacked["val"]; > > ...the output value is "-333371788". (???) Which tells me that PHP is > NOT unpacking $msg as an unsigned long integer, but rather as > a signed > integer (since unsigned integers cannot be negative). > > Now, thanks to your suggestions, I can convert that number back to an > unsigned integer-or at least make it positive. But I > shouldn't have to > convert it, should I? Yes. Whether an integer is signed or unsigned is simply a matter of how you interpret the 32 bits representing it -- unsigned 3961595508 is represented in 32 bits in exactly the same way as signed -333371788. This explains the results you are getting: PHP *is* unpacking your binary(?) data as unsigned, but, as PHP doesn't have an unsigned type, the only place it has to put the resulting 32-bit representation is in a PHP integer, which is signed -- so when you print it, you get the signed representation. To get PHP to print the unsigned representation of an integer, you can use the %u format specifier of sprintf() (http://www.php.net/sprintf) or one of its *printf friends. Cheers! Mike --------------------------------------------------------------------- Mike Ford, Electronic Information Services Adviser, Learning Support Services, Learning & Information Services, JG125, James Graham Building, Leeds Metropolitan University, Headingley Campus, LEEDS, LS6 3QS, United Kingdom Email: m.ford@leedsmet.ac.uk Tel: +44 113 283 2600 extn 4730 Fax: +44 113 283 3211