Re: binary number
From: Mike Wahler (mkwahler_at_mkwahler.net)
Date: 09/02/04
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Date: Wed, 01 Sep 2004 23:22:24 GMT
"Kai-Uwe Bux" <jkherciueh@gmx.net> wrote in message
news:ch5ea1$6t7$1@murdoch.acc.Virginia.EDU...
> Mike Wahler wrote:
>
> >
> > "red floyd" <no.spam@here.dude> wrote in message
> > news:KWmZc.14518$AX6.13446@newssvr29.news.prodigy.com...
> >> Risto Lankinen wrote:
> >> >
> >> > [By the way, C and C++ are perhaps the only programming languages
> >> > having no token representing decimal zero! :-]
> >> >
> >> > - Risto -
> >> >
> >> >
> >>
> >> what would the token 0 be, then?
> >
> > Octal zero. (it begins with the '0' character).
> >
> >
> >
> > -Mike
>
> I am confused?
Perhaps.
> What exactly is the difference between the numerical constant 0_8 denoted
0_8 is not a numerical constant. It's not a valid C++ token at all.
> by the string "0"
A string is not a numeric literal, it's a string literal.
> in octal notation
In C++, octal notation is expressed by the first digit being zero.
>versus the numerical constant 0_10.
0_10 is not a numerical constant. It's not a valid C++ token at all.
> denoted by the string "0"
A string is not a numeric literal, it's a string literal.
> is decimal notation
In C++, decimal notation is expressed by the first digit being
1, 2, 3, 4, 5, 6, 7, 8, or 9
>(as existent in other
> languages).
This is C++, not other languages.
>In particular, what is
>
> 0_8 - 0_10
>From a C++ perspective, it's gibberish.
>From the C++ standard:
================= begin quote ================
ISO/IEC 14882:1998(E)
2.13.1 Integer literals
integer-literal:
decimal-literal integer-suffix opt
octal-literal integer-suffix opt
hexadecimal-literal integer-suffix opt
decimal-literal:
nonzero-digit
decimal-literal digit
octal-literal:
0
octal-literal octal-digit
hexadecimal-literal:
0x hexadecimal-digit
0X hexadecimal-digit
hexadecimal-literal hexadecimal-digit
nonzero-digit: one of
1 2 3 4 5 6 7 8 9
octal-digit: one of
0 1 2 3 4 5 6 7
hexadecimal-digit: one of
0 1 2 3 4 5 6 7 8 9
a b c d e f
A B C D E F
integer-suffix:
unsigned-suffix longs-uffix opt
long-suffix unsigned-suffix opt
unsigned-suffix: one of
u U
long-suffix: one of
l L
1 An integer literal is a sequence of digits that has no period
or exponent part. An integer literal may have a prefix that
specifies its base and a suffix that specifies its type. The
lexically first digit of the sequence of digits is the most
significant. A decimal integer literal (base ten) begins with
a digit other than 0 and consists of a sequence of decimal
digits. An octal integer literal (base eight) begins with the
digit 0 and consists of a sequence of octal digits. (22)
A hexadecimal integer literal (base sixteen) begins with 0x
or 0X and consists of a sequence of hexadecimal digits, which
include the decimal digits and the letters a through f and A
through F with decimal values ten through fifteen. [Example:
the number twelve can be written 12, 014, or 0XC. ]
2 The type of an integer literal depends on its form, value, and
suffix. If it is decimal and has no suffix, it has the first of
these types in which its value can be represented: int, long int;
if the value cannot be represented as a long int, the behavior
is undefined. If it is octal or hexadecimal and has no suffix,
it has the first of these types in which its value can be
represented: int, unsigned int, long int, unsigned long int.
If it is suffixed by u or U, its type is the first of these
types in which its value can be represented: unsigned int,
unsigned long int. If it is suffixed by l or L, its type is the
first of these types in which its value can be represented: long
int, unsigned long int. If it is suffixed by ul, lu, uL, Lu, Ul,
lU, UL, or LU, its type is unsigned long int. 3 A program is
illformed if one of its translation units contains an integer
literal that cannot be represented by any of the allowed types.
(21) The term "literal" generally designates, in this International
Standard, those tokens that are called "constants" in ISO C.
(22) The digits 8 and 9 are not octal digits.
================= end quote ==================
The base of literal 0 doesn't really matter, since zero is zero,
whatever the base.
-Mike
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