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Posted by Gary L. Burnore on 10/17/07 21:42
On Wed, 17 Oct 2007 16:33:26 -0500, "Bint" <bint@csgs.com> wrote:
[top posting corrected - please don't top post]
>
>
>"Lars Eighner" <usenet@larseighner.com> wrote in message
>news:slrnfhcucm.157i.usenet@debranded.larseighner.com...
>> 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.
>Well, let me ask you. I've got the code working now, using the method I
>described above. But just for my edification, how do I know if I am working
>with strings or arrays?
A string is an array and an array is an array.
>
>The thing begins as a POST incoming variable, say $image.
>Then if I start accessing elements of it, ie $image[0], $image[1], etc, then
>am I accessing string elements?
Yes, if the value in $image is a string.
>And if I make a *new* entity, say $output, and start saying things like
>$output[0] = ord($image[0]) + (ord($image[1])<<8), then am I creating a
>string there, or an array?
Yes.
Here, read this: http://us.php.net/manual/en/language.types.array.php
--
gburnore at DataBasix dot Com
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