Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c++ > #70744

Re: What is the data structure of a NULL?

Path csiph.com!eternal-september.org!feeder.eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail
From Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups comp.lang.c++
Subject Re: What is the data structure of a NULL?
Date Sat, 28 Dec 2019 13:22:46 -0800
Organization None to speak of
Lines 33
Message-ID <87o8vsqh5l.fsf@nosuchdomain.example.com> (permalink)
References <qu5spt$ad8$1@dont-email.me> <87sgl4rc3w.fsf@nosuchdomain.example.com> <slrnr0epst.sjg.nedlatham@woden.valhalla.oz>
Mime-Version 1.0
Content-Type text/plain
Injection-Info reader02.eternal-september.org; posting-host="8d88aa08a0f2992ca9bb73f0d3f59382"; logging-data="10896"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+STlOJaGPGGr+BOX+oqfKH"
User-Agent Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux)
Cancel-Lock sha1:WYXj/9JC7R092p4tQFou9M0exNY= sha1:RxL763ZA4iScllQn1KVLf/8RoWg=
Xref csiph.com comp.lang.c++:70744

Show key headers only | View raw

Ned Latham <nedlatham@woden.valhalla.oz> writes:
> Keith Thompson wrote:
>> T writes:
>> >
>> > In C++, when you make a call to Windows Kernel32.dll
>> > and it wants a NULL for one or more of its parameters,
>> > what exactly is the structure of a NULL?  A 32 bit
>> > word full of zeros?
>>
>> You might get better answers if you explained why you want to know.
>>
>> If you're making a call from C++, you can just pass a null pointer
>> value such as nullptr or NULL.  The compiler needs to know how
>> it's represented.  You probably don't.
>
> But knowing it can be useful, I use (void*) to cast integers and
> unsigned integers for functions that require pointer parameters,
> and if (parm) to test them.

Why?  Can you share some examples?

If a function takes a pointer parameter, you need to pass a pointer
value to it.  There are cases where it might make sense to cast
an integer to void*, but they're rare.  If you need to pass a null
pointer, use nullptr or NULL.  (In some low-level code, you might
store pointer values in integers.)  As for `if (parm)`, that's
valid for any scalar type.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
    [Note updated email address]
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */

Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-27 13:24 -0800
  Re: What is the data structure of a NULL? Ian Collins <ian-news@hotmail.com> - 2019-12-28 10:36 +1300
    Re: What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-27 13:55 -0800
      Re: What is the data structure of a NULL? Bo Persson <bo@bo-persson.se> - 2019-12-28 11:28 +0100
    Re: What is the data structure of a NULL? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-12-27 20:50 -0500
      Re: What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-28 17:14 -0800
      Re: What is the data structure of a NULL? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-10 20:56 -0800
  Re: What is the data structure of a NULL? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-12-27 22:42 +0100
    Re: What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-27 13:55 -0800
      Re: What is the data structure of a NULL? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-12-27 23:10 +0100
      Re: What is the data structure of a NULL? Öö Tiib <ootiib@hot.ee> - 2019-12-27 14:15 -0800
        Re: What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-27 14:24 -0800
          Re: What is the data structure of a NULL? Öö Tiib <ootiib@hot.ee> - 2019-12-27 14:41 -0800
          Re: What is the data structure of a NULL? Manfred <noname@add.invalid> - 2019-12-28 20:11 +0100
            Re: What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-28 17:16 -0800
              Re: What is the data structure of a NULL? Manfred <noname@invalid.add> - 2019-12-29 17:52 +0100
                Re: What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-29 12:21 -0800
      Re: What is the data structure of a NULL? Bart <bc@freeuk.com> - 2019-12-28 01:46 +0000
        Re: What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-28 17:17 -0800
          Re: What is the data structure of a NULL? Bart <bc@freeuk.com> - 2019-12-29 01:42 +0000
            Re: What is the data structure of a NULL? T <T@invalid.invalid> - 2019-12-28 18:39 -0800
  Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-28 02:14 -0800
    Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-28 08:33 -0600
      Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-28 13:22 -0800
        Re: What is the data structure of a NULL? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-12-28 16:02 -0800
          Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-28 22:37 -0600
        Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-28 22:37 -0600
          Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-28 21:12 -0800
            Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-29 04:45 -0600
              Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-29 13:31 -0800
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-29 21:34 -0600
                Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-29 22:48 -0800
              Re: What is the data structure of a NULL? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-12-29 20:20 -0500
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-29 21:50 -0600
                Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-29 22:46 -0800
                Re: What is the data structure of a NULL? David Brown <david.brown@hesbynett.no> - 2019-12-30 10:25 +0100
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-30 05:20 -0600
                Re: What is the data structure of a NULL? David Brown <david.brown@hesbynett.no> - 2019-12-30 17:24 +0100
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-30 17:22 -0600
                Re: What is the data structure of a NULL? David Brown <david.brown@hesbynett.no> - 2019-12-31 13:57 +0100
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-31 07:33 -0600
                Re: What is the data structure of a NULL? David Brown <david.brown@hesbynett.no> - 2019-12-31 15:45 +0100
                Re: What is the data structure of a NULL? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-12-30 18:16 +0000
                Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-30 10:45 -0800
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-30 17:29 -0600
                Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-30 21:48 -0800
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-30 04:19 -0600
                Re: What is the data structure of a NULL? David Brown <david.brown@hesbynett.no> - 2019-12-30 17:27 +0100
                Re: What is the data structure of a NULL? Öö Tiib <ootiib@hot.ee> - 2019-12-30 03:25 -0800
                Re: What is the data structure of a NULL? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-12-31 21:54 +0000
                Re: What is the data structure of a NULL? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-12-30 06:03 -0800
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-30 17:01 -0600
                Re: What is the data structure of a NULL? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-12-30 21:42 -0500
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-31 06:03 -0600
                Re: What is the data structure of a NULL? Öö Tiib <ootiib@hot.ee> - 2019-12-31 06:17 -0800
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-31 10:46 -0600
                Re: What is the data structure of a NULL? Melzzzzz <Melzzzzz@zzzzz.com> - 2019-12-31 16:57 +0000
                Re: What is the data structure of a NULL? David Brown <david.brown@hesbynett.no> - 2019-12-31 18:15 +0100
                Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-31 11:20 -0800
                Re: What is the data structure of a NULL? David Brown <david.brown@hesbynett.no> - 2020-01-01 17:01 +0100
                Re: What is the data structure of a NULL? Ned Latham <nedlatham@woden.valhalla.oz> - 2019-12-31 11:21 -0600
                Re: What is the data structure of a NULL? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-12-31 21:37 +0000
                Re: What is the data structure of a NULL? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-12-31 15:21 -0800
                Re: What is the data structure of a NULL? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-12-31 17:26 +0000
                Re: What is the data structure of a NULL? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-12-31 23:30 -0500
                Re: What is the data structure of a NULL? Manfred <noname@add.invalid> - 2020-01-01 18:10 +0100
                Re: What is the data structure of a NULL? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-01 12:21 -0500
                Re: What is the data structure of a NULL? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-12-31 15:20 +0000
                Re: What is the data structure of a NULL? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2019-12-31 11:11 -0800
                Re: What is the data structure of a NULL? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-12-31 19:47 +0000
                Re: What is the data structure of a NULL? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-12-31 10:27 -0800

csiph-web