Re: Implicit String-Literal Concatenation

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: Implicit String-Literal Concatenation
Date	2024-02-28 17:12 -0800
Organization	None to speak of
Message-ID	<87ttlst6os.fsf@nosuchdomain.example.com> (permalink)
References	(5 earlier) <urn6sv$3s62i$2@dont-email.me> <877ciouua2.fsf@nosuchdomain.example.com> <uroe02$4eoh$1@dont-email.me> <87y1b4tbcq.fsf@nosuchdomain.example.com> <urok6t$5lv4$1@dont-email.me>

Show all headers | View raw

bart <bc@freeuk.com> writes:
> On 28/02/2024 23:31, Keith Thompson wrote:
>> bart <bc@freeuk.com> writes:
>>> It would be unfortunate if your example was allowed. Clearly a binary
>>> representation of an instance of your struct would probably require 16
>>> bytes rather than 4, of which one may be padding.
>> Depending on the sizes and alignments of the various types, sure.
>> So what?
>
>> If you have suggestions for alternate ways to define #embed, they might
>> be interesting, but it's too late to change the existing specification.
>
> My early comments on this were about compiler performance. I suggested
> there might be a way to turn 100,000 byte values in a file, directly 
> into a 100KB string or data block, without needing to first convert
> 100,000 values into 100,000 integer expressions representated as
> tokens, and to then parse those 100,000 expressions into AST nodes
> etc.

I suggest that (a) parsing thoser 100,000 byte values isn't likely to be
a huge deal (if you have actual performance figures that contradict
that, feel free to present them), and (b) any solution that doesn't
involve expanding to C source code would require a lot more work to
implement for very little benefit.

> DB suggested something like that was actually done. But you can't do
> that if those 100,000 numbers represent from 100KB to 800KB of memory 
> depending on the data type of the strucure they're initialising.

Neither gcc nor clang implements #embed yet.  DB mentioned prototype
implementations.  I've asked him for more information.

> They might even be mixed type. Or it might be an example like this:
>
> A binary file contains 8 byes representing one IEEE754 float
> value. It is desired to use that to initialise a double array of one
> element.
>
> However #embed will that into 8 integer values of 0 to 255 each (I assume).

Assuming CHAR_BIT==8, yes.  You can use it to initialize a union, or use
memcpy() to copy from an array of unsigned char into a double object.
(Storing double values in binary files is uncommon, but it's certainly
possible.)

> It's not clear either what happens when one of the integers has the
> value 150, say, but it is used to initialise an element of type
> (signed) char. It sounds like it would make it hard to inialise a
> char[] array, when char is signed, from a file of UTF8 text.

Say you have a binary file containing a single byte with the value 150
(when interpreted as an 8-bit unsigned char).  Then
    #embed "file.dat"
will expand to something like
    150
or
    0x96

So if you write:

    char array[] = {
#embed file.dat
    };

then it's treated exactly the same as
    char array[] = { 150 };

If plain char is signed, then the result of the conversion is
implementation-defined, but is very very likely to result in a value of
-106.

I expect that 99% of the uses of #embed will be to initialize arrays of
unsigned char (or uint8_t).  For that purpose, it should work just fine.

> Basically, #embed is dumb.

Do you object to the fact that the authors didn't add additional
arbitrary restrictions to forbid uses that you don't like?

> For flexibility, I wouldn't use #embed at all. Just have an actual
> comma-separated set of values in a text file, and use #include
> instead.

And you can still do that.

If you have a png image file and you want to include its contents in
your C program, you can use a separate program to translate the file to
C source and #include the result, or you can use `#embed "foo.png"`.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Medtronic
void Void(void) { Void(); } /* The recursive call of the void */

Thread

Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-24 23:05 +0000
  Re: Implicit String-Literal Concatenation Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-02-25 17:38 +0100
    Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-25 20:43 +0000
      Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-25 21:20 +0000
  Re: Implicit String-Literal Concatenation Blue-Maned_Hawk <bluemanedhawk@invalid.invalid> - 2024-02-25 16:45 +0000
  Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-25 20:25 +0000
  Re: Implicit String-Literal Concatenation Łukasz 'Maly' Ostrowski <l3vi4than@gmail.com> - 2024-02-26 21:12 +0100
    Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-26 20:31 +0000
      Re: Implicit String-Literal Concatenation Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-02-27 13:18 +0100
        Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-27 23:10 +0000
          Re: Implicit String-Literal Concatenation Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-02-28 00:50 +0100
  Re: Implicit String-Literal Concatenation Kaz Kylheku <433-929-6894@kylheku.com> - 2024-02-26 20:42 +0000
  Re: Implicit String-Literal Concatenation porkchop@invalid.foo (Mike Sanders) - 2024-02-26 22:03 +0000
    Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-26 23:17 +0000
      Re: Implicit String-Literal Concatenation porkchop@invalid.foo (Mike Sanders) - 2024-02-27 17:27 +0000
    Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-27 09:36 +0100
      Re: Implicit String-Literal Concatenation porkchop@invalid.foo (Mike Sanders) - 2024-02-27 17:31 +0000
      Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-27 18:56 +0000
        Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-27 23:21 +0100
          Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-27 22:52 +0000
            Re: Implicit String-Literal Concatenation Kaz Kylheku <433-929-6894@kylheku.com> - 2024-02-28 01:09 +0000
              Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-28 12:50 +0100
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-28 20:56 +0000
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-28 21:34 +0000
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-28 23:52 +0000
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-29 00:15 +0000
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-29 02:53 +0000
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-29 09:20 +0000
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-02-29 15:48 +0000
                Re: Implicit String-Literal Concatenation Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-02-29 17:03 +0100
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-02-29 16:17 +0000
                Re: Implicit String-Literal Concatenation Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-02-29 18:12 +0100
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-02-29 17:30 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 13:20 -0800
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-29 21:44 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 14:06 -0800
                Re: Implicit String-Literal Concatenation Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-01 18:09 +0100
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-01 10:49 -0800
                Re: Implicit String-Literal Concatenation Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-01 22:06 +0100
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 09:20 -0800
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-29 08:58 +0100
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-29 21:05 +0000
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-03-01 09:16 +0100
                Re: Implicit String-Literal Concatenation Kaz Kylheku <433-929-6894@kylheku.com> - 2024-03-01 16:55 +0000
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-03-01 18:28 +0100
      Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-27 20:25 +0000
        Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-27 12:35 -0800
          Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-27 23:03 +0000
        Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-27 22:12 +0000
          Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-28 12:54 +0100
            Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-28 13:13 +0000
              Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-28 15:08 +0100
              Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-28 13:36 -0800
                Re: Implicit String-Literal Concatenation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-02-29 11:56 +0000
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-29 16:19 +0100
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-29 21:36 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 13:53 -0800
                Re: Implicit String-Literal Concatenation Richard Harnden <richard.nospam@gmail.invalid> - 2024-03-01 12:59 +0000
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-03-01 20:59 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 08:08 -0800
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-29 14:31 +0000
                Re: Implicit String-Literal Concatenation Richard Harnden <richard.nospam@gmail.invalid> - 2024-02-29 15:22 +0000
                Re: Implicit String-Literal Concatenation "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-02-29 13:10 -0800
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 13:45 -0800
                Re: Implicit String-Literal Concatenation "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-02-29 14:03 -0800
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 14:14 -0800
                Re: Implicit String-Literal Concatenation "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-02 13:48 -0800
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-03-05 04:48 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-04 20:55 -0800
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-03-07 21:08 +0000
                Re: Implicit String-Literal Concatenation Kaz Kylheku <433-929-6894@kylheku.com> - 2024-03-07 21:44 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-07 14:25 -0800
                Re: Implicit String-Literal Concatenation Kaz Kylheku <433-929-6894@kylheku.com> - 2024-03-07 23:00 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-07 15:46 -0800
                Re: Implicit String-Literal Concatenation "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-07 16:17 -0800
                Re: Implicit String-Literal Concatenation Richard Harnden <richard.nospam@gmail.invalid> - 2024-03-08 00:26 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-07 14:16 -0800
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-29 16:30 +0100
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 08:25 -0800
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 08:18 -0800
                Re: Implicit String-Literal Concatenation Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-02-29 18:17 +0100
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 09:22 -0800
                Re: Implicit String-Literal Concatenation Kaz Kylheku <433-929-6894@kylheku.com> - 2024-02-29 19:26 +0000
                Re: Implicit String-Literal Concatenation James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-02-29 14:45 -0500
              Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-28 13:41 -0800
            Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-28 13:57 -0800
              Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-28 23:01 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-28 15:31 -0800
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-29 00:47 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-28 17:12 -0800
                Re: Implicit String-Literal Concatenation tTh <tth@none.invalid> - 2024-02-29 16:29 +0100
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-02-29 16:15 +0000
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-02-29 15:53 +0000
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 09:06 -0800
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-02-29 17:28 +0000
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-29 18:58 +0100
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-02-29 18:05 +0000
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-02-29 18:09 +0000
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-02-29 21:27 +0000
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-03-01 11:52 +0000
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-03-05 04:47 +0000
                Re: Implicit String-Literal Concatenation scott@slp53.sl.home (Scott Lurndal) - 2024-03-05 15:09 +0000
                Re: Implicit String-Literal Concatenation Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-03-06 01:49 +0000
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-29 20:51 +0100
              Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-29 10:10 +0100
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-02-29 10:18 +0000
                Re: Implicit String-Literal Concatenation tTh <tth@none.invalid> - 2024-02-29 16:34 +0100
                Re: Implicit String-Literal Concatenation bart <bc@freeuk.com> - 2024-03-01 11:58 +0000
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-03-01 13:17 +0100
                Re: Implicit String-Literal Concatenation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-02-29 09:03 -0800
                Re: Implicit String-Literal Concatenation David Brown <david.brown@hesbynett.no> - 2024-02-29 19:08 +0100

csiph-web