Re: [PHP] unpacking an array of structs...

In the desktop app's memory the data is packed end-to-end already:

typedef struct MANGOpie
{
    unsigned char  mango;
    unsigned short  pie;
}
MANGOpie;

MANGOpie * pies = (MANGOpie *)malloc(count*sizeof(MANGOpie));


...and the entire 'pies' array is sent to the PHP script as binary data 
using PUT.






On February 23, 2010, Nathan Nobbe <[email protected]> wrote:

> On Monday, February 22, 2010, [email protected] <[email protected]> wrote:
>> 
>> I have a desktop app that has a data structure that looks like this:
>> 
>> typedef struct MANGOpie
>> {
>>    unsigned char   mango;
>>    unsigned short  pie;
>> }
>> MANGOpie;
>> 
>> 
>> 
>> I manage a C array of these things in memory:
>> 
>> MANGOpie * pies = (MANGOpie *)malloc(count*sizeof(MANGOpie));
>> 
>> 
>> 
>> 
>> I pass these to a PHP script on my webserver who needs to unpack the 
>> array of structs.
>> 
>> The unpack() PHP function appears to be what I need, but it doesn't 
>> like the formatting I'm using to describe an array of these structs:
>> 
>> "(Cmango/npie)*"
>> 
>> What it doesn't like are the parentheses.  I've tried brackets and 
>> curlies too, but nothing works.  I have to have the parentheses to 
>> tell the parser to repeat the entire struct:
>> 
>> mango
>> pie
>> mango
>> pie
>> mango
>> pie
>> ...
>> 
>> 
>> 
>> Formatting without the parentheses -- "Cmango/npie*" -- is:
>> 
>> mango
>> pie
>> pie
>> pie
>> pie
>> pie
>> ...
>> 
>> 
>> 
>> One workaround is to drop the struct and just manage two separate 
>> parallel arrays of each data type in the desktop app:
>> 
>> unsigned char *   mangos = (unsigned char 
>>  *)malloc(count*sizeof(unsigned char));
>> unsigned short *  pies   = (unsigned short 
>> *)malloc(count*sizeof(unsigned short));
>> 
>> With PHP unpack() format strings:
>> 
>> "Cmango*"
>> "npie*"
>> 
>> But, I'd rather keep the struct for the sake of code clarity and neatness.
>> 
>> 
>> 
>> Another would be to iterate thru the binary data, unpacking one 
>> struct at a time, but that would be slower, presumably.
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> Anyone know the trick to this?
> 
> 
> I'm curious how you are getting to the point of calling pack() in the
> first place.  can we see the bit of your script that interacts with
> this c code?
> 
> -nathan
> 
>