warning: dereferencing type-punned pointer will break strict-aliasing rules

Wall로 Build 를 하는데 아래와 같은 워닝이 발생해서

warning: dereferencing type-punned pointer will break strict-aliasing rules

구글링좀 하고, 고치기 귀찮아서  MakeFile만 수정해서 올림
연구원 씨가 관심 있으면 고치겠지.....



The following short examples demonstrate my problem:

----Exhibit A
#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int foo;
    int bar;
} item_t;

int return_item (void **item);

int return_item (void **item)
{
    void *mem;

    mem = malloc (1);
    if (mem) {
        *item = mem;
        return 0;
    }
    else
        return 1;
}

int main (int argc, char *argv[])
{
    item_t *item;

    if (return_item ((void **)&item) == 0) {
        printf ("%p\n", item);
        free (item);
    }

    return 0;
}

----Exhibit B
#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int foo;
    int bar;
} item_t;

int return_item (void **item);

int return_item (void **item)
{
    void *mem;

    mem = malloc (1);
    if (mem) {
        *item = mem;
        return 0;
    }
    else
        return 1;
}

int main (int argc, char *argv[])
{
    item_t *item;
    void *item_temp;

    if (return_item (&item_temp) == 0) {
        item = item_temp;
        printf ("%p\n", item);
        free (item);
    }

    return 0;
}
----

The code is a generic example of the problem.  The real code that is
producing the problem is a hashing API which hashes (void *) and hence
uses (void **) as an out parameter type. 

Exhibit A produces a warning as follows:

[nodbug:mato]$ gcc -O2 -Wall -o aliasing-test aliasing-test.c
aliasing-test.c: In function `main':
aliasing-test.c:28: warning: dereferencing type-punned pointer will break strict-aliasing rules

I'm using gcc version 3.3.5 (Debian 1:3.3.5-13) but the problem persists
even when tested with GCC 4.x on newer systems.

Exhibit B is my proposed "fix".  Can anyone advise if the code in
Exhibit A is legitimate, i.e. whether or not it's really violating the
strict aliasing rules as defined by the C standard?  If not, then I
guess the warning is spurious and I can safely use the fix.

If the code is in fact violating the standard then feel free to
enlighten me how to fix it, since it seems like a legitimate thing to do
:-)

Thanks very much for any help,
귀차나서 그대로 긁어 왔습니다.

참고 : http://gcc.gnu.org/ml/gcc-help/2006-08/msg00236.html


음 문제가 되면 삭제 하겠습니다 훗..