Hex string literals (was Re: C23 thoughts and opinions)

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Hex string literals (was Re: C23 thoughts and opinions)
Date	2024-06-16 16:48 -0700
Organization	None to speak of
Message-ID	<87iky830v7.fsf_-_@nosuchdomain.example.com> (permalink)
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
[...]
> uc"..." string literals might be made even simpler, for example allowing
> only hex digits and not requiring \x (uc"01020304" rather than
> uc"\x01\x02\x03\x04").  That's probably overkill.  uc"..."  literals
> could be useful in other contexts, and programmers will want
> flexibility.  Maybe something like hex"01020304" (embedded spaces could
> be ignored) could be defined in addition to uc"\x01\x02\x03\x04".
[...]

*If* hexadecimal string literals were to be added to a future version
of the language, I think I have a syntax that I like better than
what I suggested.

Inspired by the existing syntax for integer and floating-point
hex constants, I propose using a "0x" prefix.  0x"deadbeef" is an
expression of type `const unsigned char[4]` (assuming CHAR_BIT==8),
with values 0xde, 0xad, 0xbe, 0xef in that order.  Byte order is
irrelevant; we're specifying byte values in order, not bytes of
the representation of some larger type.  memcpy()ing 0x"deadbeef"
to a uint32 might yield either 0xdeadbeef or uxefbeadde (or other
more exotic possibilities).

Again, unlike other string literals, there is no implicit terminating
null byte.  And I suggest making them const, since there's no
existing code to break.

If CHAR_BIT==8, each byte is represented by two hex digits.  More
generally, each byte is represented by (CHAR_BIT+3)/4 hex digits in
the absence of whitespace.  Added whitespace marks the end of a byte,
0x"deadbeef" is 1, 2, 3, or 4 bytes if CHAR_BIT is 32, 16, 12, or 8
respectively, but 0x"de ad be ef" is 4 bytes regardless of CHAR_BIT.
0x"" is a syntax error, since C doesn't support zero-length arrays.
Anything between the quotes other than hex digits and spaces is a
syntax error.

0x"dead beef" is still 4 bytes if CHAR_BIT==8; the space forces the
end of a byte, but the usage of spaces doesn't have to be consistent.

This could be made more flexible by allowing various backslash
escapes, but I'm not inclined to complicate it too much.

Note that the value of a (proposed) hex string literal is not a
string unless it happens to end in zero.  I still use the term
"string literal" because it's closely tied to existing string
literal syntax, and existing string literals don't necessarily
represent strings anyway ("embedded\0null\0characters").

Binary string literals 0b"11001001" might also be worth
considering (that's of type `const unsigned char[1]`).  Octal
string literals 0"012 345 670" *might* be worth considering.
<https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3193.htm>
proposes a new "0o123" syntax for octal constants; if that's adopted,
I propose allowing 0o"..." and *not" 0"...".  I'm not sure whether
to suggest hex only, or doing hex, octal, and binary for the sake
of completeness.

What I'm trying to design here is a more straightforward way to
represent raw (unsigned char[]) data in C code, largely but not
exclusively for use by #embed.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */

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Re: C23 thoughts and opinions Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-14 14:30 -0700
  Re: C23 thoughts and opinions bart <bc@freeuk.com> - 2024-06-14 23:39 +0100
    Re: C23 thoughts and opinions David Brown <david.brown@hesbynett.no> - 2024-06-15 19:17 +0200
      Re: C23 thoughts and opinions bart <bc@freeuk.com> - 2024-06-15 20:27 +0100
        Re: C23 thoughts and opinions Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-15 22:39 +0000
          Re: C23 thoughts and opinions bart <bc@freeuk.com> - 2024-06-16 00:20 +0100
            Re: C23 thoughts and opinions Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-16 01:16 +0000
            Re: C23 thoughts and opinions "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-16 12:31 -0700
              Re: C23 thoughts and opinions Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-17 00:03 +0000
        Re: C23 thoughts and opinions David Brown <david.brown@hesbynett.no> - 2024-06-16 16:54 +0200
          Re: C23 thoughts and opinions bart <bc@freeuk.com> - 2024-06-16 20:00 +0100
            Re: C23 thoughts and opinions David Brown <david.brown@hesbynett.no> - 2024-06-17 10:49 +0200
            Re: C23 thoughts and opinions Michael S <already5chosen@yahoo.com> - 2024-06-17 13:18 +0300
  Re: C23 thoughts and opinions David Brown <david.brown@hesbynett.no> - 2024-06-15 17:58 +0200
    Re: C23 thoughts and opinions Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-15 22:37 +0000
      Re: C23 thoughts and opinions David Brown <david.brown@hesbynett.no> - 2024-06-16 16:55 +0200
  Hex string literals (was Re: C23 thoughts and opinions) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-16 16:48 -0700
    Re: Hex string literals (was Re: C23 thoughts and opinions) David Brown <david.brown@hesbynett.no> - 2024-06-17 11:42 +0200
      Re: Hex string literals (was Re: C23 thoughts and opinions) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-17 17:19 -0700
        Re: Hex string literals (was Re: C23 thoughts and opinions) Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-18 04:19 +0000
          Re: Hex string literals (was Re: C23 thoughts and opinions) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-17 22:39 -0700
        Re: Hex string literals (was Re: C23 thoughts and opinions) David Brown <david.brown@hesbynett.no> - 2024-06-18 15:54 +0200
          Re: Hex string literals (was Re: C23 thoughts and opinions) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-18 15:00 -0700
            Re: Hex string literals (was Re: C23 thoughts and opinions) David Brown <david.brown@hesbynett.no> - 2024-06-19 09:37 +0200
              Re: Hex string literals (was Re: C23 thoughts and opinions) Kaz Kylheku <643-408-1753@kylheku.com> - 2024-06-19 10:17 +0000
                Re: Hex string literals (was Re: C23 thoughts and opinions) Michael S <already5chosen@yahoo.com> - 2024-06-19 13:44 +0300
                Re: Hex string literals (was Re: C23 thoughts and opinions) bart <bc@freeuk.com> - 2024-06-19 11:57 +0100
                Re: Hex string literals (was Re: C23 thoughts and opinions) scott@slp53.sl.home (Scott Lurndal) - 2024-06-19 13:46 +0000
                Re: Hex string literals (was Re: C23 thoughts and opinions) Michael S <already5chosen@yahoo.com> - 2024-06-19 18:02 +0300
          Re: Hex string literals (was Re: C23 thoughts and opinions) Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-19 07:25 +0000
            Re: Hex string literals (was Re: C23 thoughts and opinions) David Brown <david.brown@hesbynett.no> - 2024-06-19 10:49 +0200
              Re: Hex string literals (was Re: C23 thoughts and opinions) Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-21 07:13 +0000
                Re: Hex string literals (was Re: C23 thoughts and opinions) David Brown <david.brown@hesbynett.no> - 2024-06-21 13:06 +0200
                Re: Hex string literals (was Re: C23 thoughts and opinions) Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-21 22:48 +0000
                Re: Hex string literals (was Re: C23 thoughts and opinions) David Brown <david.brown@hesbynett.no> - 2024-06-22 13:40 +0200
                Re: Hex string literals (was Re: C23 thoughts and opinions) James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-06-21 10:15 -0400
            Re: Hex string literals (was Re: C23 thoughts and opinions) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-19 02:32 -0700
      Re: Hex string literals (was Re: C23 thoughts and opinions) Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-18 04:19 +0000
    Re: Hex string literals (was Re: C23 thoughts and opinions) Richard Kettlewell <invalid@invalid.invalid> - 2024-06-17 11:41 +0100
      Re: Hex string literals (was Re: C23 thoughts and opinions) Richard Kettlewell <invalid@invalid.invalid> - 2024-06-17 14:57 +0100
      Re: Hex string literals (was Re: C23 thoughts and opinions) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-17 18:57 -0700
        Re: Hex string literals (was Re: C23 thoughts and opinions) Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-18 08:12 +0000
        Re: Hex string literals (was Re: C23 thoughts and opinions) Richard Kettlewell <invalid@invalid.invalid> - 2024-06-18 16:14 +0100
    Re: Hex string literals (was Re: C23 thoughts and opinions) bart <bc@freeuk.com> - 2024-06-17 14:21 +0100
      Re: Hex string literals (was Re: C23 thoughts and opinions) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-17 19:20 -0700
      Re: Hex string literals (was Re: C23 thoughts and opinions) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-17 22:39 -0700
        Re: Hex string literals (was Re: C23 thoughts and opinions) Michael S <already5chosen@yahoo.com> - 2024-06-18 12:39 +0300
          Re: Hex string literals (was Re: C23 thoughts and opinions) bart <bc@freeuk.com> - 2024-06-18 11:28 +0100
            Re: Hex string literals (was Re: C23 thoughts and opinions) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-18 11:12 -0700
          Re: Hex string literals (was Re: C23 thoughts and opinions) David Brown <david.brown@hesbynett.no> - 2024-06-18 17:20 +0200
          Re: Hex string literals (was Re: C23 thoughts and opinions) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-18 11:04 -0700
          Re: Hex string literals (was Re: C23 thoughts and opinions) Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-20 06:51 +0000
      Re: Hex string literals (was Re: C23 thoughts and opinions) Kaz Kylheku <643-408-1753@kylheku.com> - 2024-06-18 09:50 +0000
        Re: Hex string literals (was Re: C23 thoughts and opinions) scott@slp53.sl.home (Scott Lurndal) - 2024-06-18 13:56 +0000
          Re: Hex string literals (was Re: C23 thoughts and opinions) David Brown <david.brown@hesbynett.no> - 2024-06-18 17:21 +0200
            Re: Hex string literals (was Re: C23 thoughts and opinions) Richard Harnden <richard.nospam@gmail.invalid> - 2024-06-18 19:25 +0100
              Re: Hex string literals (was Re: C23 thoughts and opinions) Richard Harnden <richard.nospam@gmail.invalid> - 2024-06-18 19:38 +0100
              Re: Hex string literals (was Re: C23 thoughts and opinions) Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-21 22:49 +0000

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