Data encapsulation in C

Question

I am currently working on an embedded system and I have a component on a board which appears two times. I would like to have one .c and one .h file for the component.

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Answer 1

I would like this data to be non-accessible from the "outside" of my component (only through special functions in my component).

You can do it in this way (a big malloc including the data):

#include 
#include 
#include 

typedef struct {
    uint32_t pin_reset;
    uint32_t pin_drdy;
    uint32_t pin_start;
    volatile avr32_spi_t *spi_module;
    uint8_t cs_id;  
} ads1248_options_t;

void fn(ads1248_options_t *x)
{
    int32_t *values = (int32_t *)(x + 1);
    /* values are not accesible via a member of the struct */

    values[0] = 10;
    printf("%d\n", values[0]);
}

int main(void)
{
    ads1248_options_t *x = malloc(sizeof(*x) + (sizeof(int32_t) * 100));

    fn(x);
    free(x);
    return 0;
}