Fully-portable version of limits.h

[Frederick Gotham]

I was pondering over writing a fully-portable version of <limits.h(e.g.
such things as:

#define UINT_MAX ((unsigned)-1)

, when something occurred to me. Just recently on this newsgroup, I and a few
others posted code which yielded a compile-time constant specifying the
amount of bits which are set in an integer expression; then I thought about
IMAX_BITS, and wondered if this is how IMAX_BITS works? Does it just count
how many bits are set?

Is it possible in C to a write a fully-portable version of <limits.h>? I'll
start off with the easy ones:

#define CHAR_BIT (IMAX_BITS((char unsigned)-1))
#define UCHAR_MAX ((char unsigned)-1 + 0)
#define USHRT_MAX ((short unsigned)-1 + 0)
#define UINT_MAX ((unsigned)-1)
#define ULONG_MAX ((long unsigned)-1)

--

Frederick Gotham

[Ben Pfaff]

Frederick Gotham <fg*******@SPAM.comwrites:

Is it possible in C to a write a fully-portable version of <limits.h>? I'll
start off with the easy ones:

#define CHAR_BIT (IMAX_BITS((char unsigned)-1))

That's not conforming. CHAR_BIT must be suitable for use in an
#if directive, but constant expressions in #if directives may not
contain casts.
--
Go not to Usenet for counsel, for they will say both no and yes.

[Frederick Gotham]

Ben Pfaff posted:

>#define CHAR_BIT (IMAX_BITS((char unsigned)-1))

That's not conforming. CHAR_BIT must be suitable for use in an
#if directive, but constant expressions in #if directives may not
contain casts.

Damn, hadn't thought of that...

--

Frederick Gotham

[Eric Sosman]

Frederick Gotham wrote:

Ben Pfaff posted:

>>>#define CHAR_BIT (IMAX_BITS((char unsigned)-1))

That's not conforming. CHAR_BIT must be suitable for use in an
#if directive, but constant expressions in #if directives may not
contain casts.

Damn, hadn't thought of that...

And as if that weren't enough, try writing a fully
portable replacement for INT_MIN. Extra credit: CHAR_MIN.

--
Eric Sosman
es*****@acm-dot-org.invalid

[Nils O. Selåsdal]

Frederick Gotham wrote:

I was pondering over writing a fully-portable version of <limits.h(e.g.
such things as:

There is no need to. It comes with the implementation.