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Placing size of array at start of array

Richard Collett

Hi all,
I am working with the TI TUSB3200, trying to modify their example code for our own USB device. USB requires many tables which start with a length byte. I would like to use the sizeof operator to calculate this for me, as shown here:

byte code rictest[] =
{
	sizeof(rictest),
	1,
	2
};
This gives the error 
warning C198: sizeof returns 0
, so plainly the compiler only does a single pass through the code, and does not know the array size until it has finished parsing the entire array definition. :(

Is there any other way to achieve this? I presume it would be possible with some sort of pre-processor macro to count the number of elements manually before defining the aray...

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  • 0

    Hmm, I think you can make use of how Keil arranges/places variables in memory. They are not arranged in order of declaration, they are arranged alphabetically. So, if you declare:

    const unsigned char myarray[] = {1,2,3,4};
    const unsigned int amyarraysize = sizeof(myarray) + 2/*include size of amyarraysize */);

    in one file, with no other declarations. amyarraysize will appear as the first in memory, followed by myarray. (Of cause myarray itself should no longer contain the size ...). Remember to move the pointer to amyarraysize, when copying.

    Now, Im not sure that it will always work, but I think so. If you really want to be sure, use the
    SECTIONS(?NC?YOURFILENAME?NCONST (addr))
    to place it to a fixed place in memory

    Best regards
    Niels Sejersen


Reply
  • 0

    Hmm, I think you can make use of how Keil arranges/places variables in memory. They are not arranged in order of declaration, they are arranged alphabetically. So, if you declare:

    const unsigned char myarray[] = {1,2,3,4};
    const unsigned int amyarraysize = sizeof(myarray) + 2/*include size of amyarraysize */);

    in one file, with no other declarations. amyarraysize will appear as the first in memory, followed by myarray. (Of cause myarray itself should no longer contain the size ...). Remember to move the pointer to amyarraysize, when copying.

    Now, Im not sure that it will always work, but I think so. If you really want to be sure, use the
    SECTIONS(?NC?YOURFILENAME?NCONST (addr))
    to place it to a fixed place in memory

    Best regards
    Niels Sejersen


Children