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Posted by Lars Eighner on 10/17/07 21:08
In our last episode,
<13hcrsv3c5a2584@corp.supernews.com>,
the lovely and talented Bint
broadcast on comp.lang.php:
> Yeah, I guess I'm trying to do something low-level with this high-level
> lanugage. I'm new to PHP so I'm trying to figure out how these fancy
> keyword-based arrays work with old-school byte arrays.
> I'm sending images wirelessly to a php script. The image, originally a grid
> of pixels, each 16-bits deep, is run-length-encoded into a smaller C array
> of unsigned shorts (16 bit words). That C array is base64 encoded into an
> ASCII string so that I can send it via HTTP POST command to a PHP script.
> The PHP script sees my base64 encoded array as a variable, which I can
> easily base64 decode into a php "array". But it is proving trickier to
> access my pixel values, because now the array is not a C array, but a PHP
> one. If I look at the value of array[0], then I don't get the number that
> was in array[0] before I sent it.
> I can work around it, by accessing each byte of the PHP array:
> $myoriginalarray[0] = ord($phparray[0]) + ord($phparray[1]) << 8;
> But that is complicated and I just thought there might be some simpler way
> of telling PHP "hey, I have an array of unsigned shorts here".
> Maybe not.
Treat them as a string, use the base 64 decode function which takes a string
argument and returns a string result. In many respects strings are a kind
of array, but they are not type array in PHP. Conveniently, strings are
composed of characters, and characters bear more than a passing resemblance
to 8-bit unsigned integers. Take them two at time if you have to manipulate
them at the 16-bit level. See chapter 11 (Types) in the manual for hints as
to how to work with strings. Don't use curly brackets, they will be
deprecated in PHP 6, or so the scuttlebutt goes.
Do not be confused by PHP array type. Although strings are kind of like
arrays with integer indices, there are significant differences. You should
be learning to use strings from the documentation on type string, and the
documentation on type array is likely to mislead you.
--
Lars Eighner <http://larseighner.com/> <http://myspace.com/larseighner>
Countdown: 460 days to go.
What do you do when you're debranded?
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