Passing pointer to a function callback

Question

I want to pass an array to a callback function, but I always get zero (sometimes garbage character) return of call_print(). My code are in two separate files below, and I like to keep it like this.

file1.c

#include <myheader.h>

uint8_t dummy[6] = {0x30, 0x30, 0x31, 0x31, 0x32, 0x32};

void dcallback(uint8_t **outputBuff)

int main(void)
{
    slave(dcallback);
}

void dcallback(uint8_t **outputBuff)
{ 
    *outputBuff = dummy;
}

file2.c

#include <myheader.h>

static void (*data_callback)(uint8_t **output_buffer);

uint8_t **output_buffer;

void slave(void (*data_callback_in)(uint8_t **output_buffer))
{
    int i;

    data_callback = data_callback_in;
    data_callback(output_buffer);

    for(i=0 ; i<6 ; i++)
    {
        call_print( **(output_buffer + i));
    }
}

When I modify the code as you can see below, I got '0 1 2 3 4 5'. This seems correct result, but this is not what I want. I want to pass an array, so that I can point the pointer to another array easily. I thought I made mistake working with pointer.

file1.c

#include <myheader.h>

uint8_t dummy[6] = {0x30, 0x30, 0x31, 0x31, 0x32, 0x32};

void dcallback(uint8_t *outputBuff)

int main(void)
{
    slave(dcallback);
}

void dcallback(uint8_t *outputBuff)
{ 
    int x;

    for(x=0 ; x<6 ; x++)
    {
        *outputBuff = x;
    }
}

file2.c

#include <myheader.h>

static void (*data_callback)(uint8_t *output_buffer);

uint8_t output_buffer[6];

void slave(void (*data_callback_in)(uint8_t *output_buffer))
{
    int i;

    data_callback = data_callback_in;
    data_callback(output_buffer);

    for(i=0 ; i<6 ; i++)
    {
        call_print(output_buffer[i]);
    }
}

Someone, could you please spot where I made mistake? How should I properly pass 'dummy' array?

Thanks before.

Answer 1

Try making uint8_t **output_buffer; as single pointer uint8_t *output_buffer;

and while calling the callback from slave method you need to call like below.

data_callback(&output_buffer);

Here is the full code.

#include<stdio.h>
#include<stdint.h>

uint8_t dummy[6] = {0x30, 0x30, 0x31, 0x31, 0x32, 0x32};

static void (*data_callback)(uint8_t **output_buffer);

uint8_t *output_buffer;
void dcallback(uint8_t **outputBuff);

int main(void)
{
    slave(dcallback);
}

void dcallback(uint8_t **outputBuff)
{
    *outputBuff = dummy;
}



void slave(void (*data_callback_in)(uint8_t **output_buffer))
{
    int i;

    data_callback = data_callback_in;
    data_callback(&output_buffer);

    for(i=0 ; i<6 ; i++)
    {
        printf("%d\n", *(output_buffer + i));
    }
}