Get the outer structure's pointer from the inner structure in C.

get_parent_ptr.c

#include <stddef.h>

typedef struct inner {
    int i_a;
    int i_b;
    int i_c;
} inner_t;

typedef struct outer {
    int o_a;
    int o_b;
    int o_c;
    inner_t o_inner;
} outer_t;

// MACRO to find the address of the outer structure
// t -> the type of the outer structure
// f -> the inner structure's field name in outer structure
// p -> pointer to the inner structure in outer structure
#define GET_PARENT(t, f, p) ((t *) ((char *) p - offsetof(t, f)))

// Example usage
void foo_function(inner_t *iptr)
{
    printf("%p\n", GET_PARENT(outer_t, o_inner, iptr));
}