CODEWITHSUNDEEP
c
asir
asir

Reputation: 15

can address be typecasted?

I want the address of structure, but in my code I am only able to return the address of value the first member. Can I typecast the address of value to struct classifier? If yes how to type cast it ? For example, my function only returns the address of value in the below mentioned struct can I cast this address to classifier?

    struct classifier
    {
        int value;
        struct packet_filter pktFltr;
        struct classifier *next;
    }

Upvotes: 1

Views: 149

Answers (3)

pmg
pmg

Reputation: 108988

If you have an object of type struct classifier, the address of that object is of type struct classifier *. There is nothing special about it ...

#include <stdio.h>

struct classifier {
    int value;
    struct packet_filter pktFltr;
    struct classifier *next;
};

void foo(struct classifier *bar) {
    printf("value is %d\n", bar->value);
}

int main(void) {
    struct classifier example = {42}; /* value is 42, everything else is 0  */
    foo(&example); /* ok, `&example` is of the correct type */
    return 0;
}

Upvotes: 0

Amarghosh
Amarghosh

Reputation: 59461

While it is guaranteed that the first member of struct will have the same address as struct itself (as padding is not permitted in the beginning), casting the return value of an int* function() to some_struct* is not a good practice - what if someone later decides to modify the function to return the address of some malloc'ed int instead?

Upvotes: 0

Milan
Milan

Reputation: 15849

The standard states that the address of a structure classifier is the same as the address of its first member value provided that you are casting it correctly.

That is, following is equivalent, p points to the same address :

int *p;
struct classifier c;

p = (int*)c;
p = &c.value;

Meaning that

(int*) c == &c.value

And in your case, if I understand it correctly you would want:

c = (struct chassifier *) adress_of_my_first_member_in_struct_classifier;

Upvotes: 1

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