C Macro that effectively does hierarchical type casting. Credit goes out to an unknown Linux kernel developer.

gistfile1.c

/*
 * Name: container_of
 * Parameters: ptr - Pointer to the inner structure that you have.
 * Parameters: type - The type of outer structure you want to have.
 * Parameters: member - The member in the outer structure for the inner.
 * Returns: type * - Pointer to the outer structure you wanted.
 * Description:
 *  This is a macro used to get to a child structure when you have a pointer
 *  to the root structure. Notice that this makes no checks or validation.
 *  Use when you know what you have and what you want.
 */
#define container_of(ptr, type, member)({ \
    const typeof( ((type *)0)->member ) *__mptr = (ptr); \
    (type *)( (char *)__mptr - offsetof(type, member) ); \
})

// I have one structure and enum
enum { VAR_NONE, VAR_FLOAT, VAR_ARRAY, VAR_STRING };

typedef struct Struct_K
{
int type;
union
{
float val;
float *array;
char string;
};
}Struct_K;
// Then
#define AFA(value) (Struct_K){.type = VAR_ARRAY, .array = (float) value}
// Then
float myArray[] = {1.0f, 2.0f, 3.0f};
// So can AFA macro directly typecast myArray for Struct_K type ?
// And can I use AFA(myArray) directly to pass as parameter that accepts Struct_K type parameter.