[sedonadev] how to pass a sedona buf array to native and back.

[keith bradley]

How does one create a sys::Buf , gets it's pointer in memory, then pass this to a native function to be filled?

Sedona (myClass.sedona):

Buf    myBuf[29]

native   int   myNative(myBuf)

Native (myKit_myComp.c):

Cell myKit_myComp_myNative(SedonaVM* vm, Cell* params)

{

  *myPointer = (void*) params[1].ival;

  // fill buffer

  // return

}

[Mateusz Klatecki]

Hi,

sys::Buf is complex class which contains size, length and byte array with data. Although it is possible to pass a pointer to a Buf object and perform an operation on it in native function, it is not trivial and I would not recommend it.

I would rather use a normal byte array and work on it native function.

myClass.sedona:

byte[29] myArray

native   int   myNative(byte[] arr)

Cell myKit_myComp_myNative(SedonaVM* vm, Cell* params)

{

  uint8_t *myPointer =  params[1].aval;

  // fill buffer

for (int i=0;i<29;i++) {

myPointer[i] = i

}

  // return

return nullCell

}

[keith bradley]

Thanks Mateusz!

I will take your advice.

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[BobWirka]

Here is an example of how a native function can access a 'Buf' object passed from a component function:

Cell MyNativeFcn_print(SedonaVM* vm, Cell* params)

{

    Cell        retval;

    uint8_t* s = params[0].aval;

    /*

     * Format of the passed 'Buf' object seems to be:

     * s[0..1] uint16_t Unknown; probably a 'handle'.

     * s[2..3] uint16_t Number of bytes.

     * s[4..n] uint8_t[] Array of bytes.

     *

     * Data is LITTLE ENDIAN.

     *

     * In the case of a string, the last character is '0', so

     * you can do a printf on s[4]. Note that '123' shows up as

     * an array of length 4, with '0' as the 4th byte.

     */

    // Print the string.

    printf("%s\n" , &s[4]);

    // And return.

    retval.ival = 0;

    return retval;

}

Bob Wirka

[keith bradley]

Thanks Bob !

I will chew on this.