#include <stdio.h>
#include <malloc.h>

typedef struct { int a; } s_t;   

int open_device(s_t **dev, int index); 

int main(void){ 
        s_t *device = NULL;
        open_device(&device, 1);
        printf("A=%d\n", device->a);
        free(device);
}

int open_device(s_t **dev, int index){
        *dev = (s_t *)malloc(sizeof(s_t));   
        (*dev)->a = 42;
        return 1;
}