Re: Endian Functions

From:
fgothamNO@SPAM.com (Frederick Gotham)
Newsgroups:
comp.std.c++
Date:
Fri, 7 Jul 2006 01:23:59 GMT
Message-ID:
<bsdrg.11176$j7.315206@news.indigo.ie>
Alberto Ganesh Barbati posted:

Frederick Gotham ha scritto:

Bob Bell posted:

I was talking about the fact that after reinterpret_cast'ing the
pointer, you then dereference it.


A char has no trap representations, and so it is safe to access the
bytes of any object in memory as if it were a char, signed char or
unsigned char:


Could you please quote the clause in the C++ standard that guarantees
that?


I was working off common-sense more than anything. Any object of any type
is stored in memory as a finite, fixed-length sequence of bytes, whereby
a byte consists of CHAR_BIT bits.

If the memory is ours to access, then there is no reason why we can't
access it in whatever way we please. Take a look at the following snippet
for instance:

    #include <cstdlib>

    int main()
    {
        void * const p = std::malloc(512);

        if(!p) return -1;

        int *p_int = (int*)p;
        double *p_double = (double*)p;
        void **p_voidptr = (void**)p;

        *p_int = 7;
        *p_double = 42.3;
        *p_voidptr = p_double + 3;

        p_int += 54;

        p_double += 87;

        p_voidptr += 123;

        *p_int = 4235;
        *p_double = 35.2352;
        *p_voidptr = &p_voidptr;

        free(p);
    }

I don't know if the Standard spells it out in black and white that you
can access memory however you like, but I don't think it has to.

PS: C-style casts are of no help, as they are defined in terms of
const_cast/static_cast/reinterpret_cast (5.4/5).


The new-style casts take up too much horizontal screen space.

--

Frederick Gotham

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