Re: [dwm] malloc'ed client in manage()

From: Matthias-Christian Ott <>
Date: Sun, 7 Sep 2008 14:39:29 +0200

Nicolas Martyanoff wrote:
> On Sun, 7 Sep 2008 11:25:53 +0200
> "Szabolcs Nagy" <> wrote:
> > On 9/6/08, Filippo Erik Negroni <> wrote:
> > > A preferable, safer and more portable way of achieving such
> > > initialisation is to use the compiler's static initialisation.
> >
> > is it because of null pointer might not be represented as zeros?
> I don't think so.
> K&R, 2nd Ed. page 102:
> "Pointers and integers are not interchangeable. Zero is the sole
> exception: the constant zero may be assigned to a pointer, and a
> pointer may be compared with the constant zero. The symbolic constant
> NULL is often used in place of zero, as a mnemonic to indicate that
> this is a special value for a pointer"
> I think it's quite explicit: the NULL macro expands to 0.

Does anyone know whether there are architectures where NULL is not equal
to 0?

See ISO/IEC 9899:TC2 Section 7.17.3:

  "The macros are NULL which expands to an implementation-defined null
   pointer constant and; ..."

See ISO/IEC 9899:TC2 Section
  "An integer constant expression with the value 0, or such an
   expression cast to type void *, is called a null pointer constant."

Seems like a contradiction in the C99 standard (I have to admit that my
version is a Committee Draft).

See ISO/IEC 14882:1998 and ISO/IEC 14882:2003 Section 4.10:
  "A null pointer constant is an integer constant expression (5.19)
   rvalue of integer type that evaluates to zero."

See ISO/IEC 14882:1998 and ISO/IEC 14882:2003 Section 18 Footnote 180:
  "Possible definitions include 0 and 0L, but not (void *)0."

And this sounds like a conflict between C and C++.

But anyhow it seems that you can't do this reliably, because s isn't
used by memset as a pointer.

memset(&s, 0, sizeof(s));

where s is a struct.

According to ISO/IEC 9899:TC2 Section and Section this
would be correct:

s = {0}; or s = 0;

Anyhow it's not working with gcc.

Received on Sun Sep 07 2008 - 12:39:29 UTC

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