Initializing a malloc'ed struct whose fields are const with run-time values

From	Noob <root@127.0.0.1>
Newsgroups	comp.lang.c
Subject	Initializing a malloc'ed struct whose fields are const with run-time values
Date	2013-01-22 16:36 +0100
Organization	A noiseless patient Spider
Message-ID	<kdmbl7$4lc$1@dont-email.me> (permalink)

Show all headers | View raw

Hello,

Is it possible, in standard C89 and C99, to initialize a
struct whose fields are const with values only known at
run-time?

For example, consider:

  struct toto { const int i; const float f; const void *p; };

Is it possible to portably implement:

  struct toto *foo(int i, float f, void *p);

which allocates space for a "struct toto", initializes it
with i, f, p and returns the address of this struct?

The best I could come up with is:

#include <stdlib.h>
#include <string.h>
struct toto *foo(int i, float f, void *p)
{
  struct toto s = { i, f, p };
  struct toto *res = malloc(sizeof *res);
  if (res != NULL) memcpy(res, &s, sizeof s);
  return res;
}

which has several defects:

1) Apparently, C89 does not allow one to use elements "not computable
at load time" in an initialization list. However, it is allowed both
in C99 (right?) and in gnu89.

2) I'm not sure it is well-defined to memcpy stuff into some const
fields. Does it tickle the cranky UB gods?

Regards.

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

Thread

Initializing a malloc'ed struct whose fields are const with run-time values Noob <root@127.0.0.1> - 2013-01-22 16:36 +0100
  Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 11:23 -0500
    Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-22 21:26 +0000
      Re: Initializing a malloc'ed struct whose fields are const with run-time values James Kuyper <jameskuyper@verizon.net> - 2013-01-22 16:41 -0500
    Re: Initializing a malloc'ed struct whose fields are const with run-time values William Ahern <william@wilbur.25thandClement.com> - 2013-01-22 13:25 -0800
      Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 23:17 -0500
    Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 13:09 +0000
      Re: Initializing a malloc'ed struct whose fields are const with run-time values Noob <root@127.0.0.1> - 2013-01-23 14:16 +0100
        Re: Initializing a malloc'ed struct whose fields are const with run-time values "BartC" <bc@freeuk.com> - 2013-01-23 13:25 +0000
          Re: Initializing a malloc'ed struct whose fields are const with run-time values Noob <root@127.0.0.1> - 2013-01-23 15:21 +0100
            Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 14:56 +0000
              Re: Initializing a malloc'ed struct whose fields are const with run-time values Noob <root@127.0.0.1> - 2013-01-23 16:40 +0100
                Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 18:26 +0000
                Re: Initializing a malloc'ed struct whose fields are const with run-time values Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-23 20:39 -0800
            Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-23 17:14 -0500
  Re: Initializing a malloc'ed struct whose fields are const with run-time values Ike Naar <ike@sverige.freeshell.org> - 2013-01-22 17:59 +0000
    Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 14:09 -0500
      Re: Initializing a malloc'ed struct whose fields are const with run-time values Noob <root@localhost> - 2013-01-22 21:59 +0100
        Re: Initializing a malloc'ed struct whose fields are const with run-time values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-01-22 21:19 +0000
        Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 23:47 -0500
      Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-22 21:05 +0000
        Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 16:15 -0500
    Re: Initializing a malloc'ed struct whose fields are const with   run-time values Ian Collins <ian-news@hotmail.com> - 2013-01-23 09:43 +1300
      Re: Initializing a malloc'ed struct whose fields are const with   run-time values William Ahern <william@wilbur.25thandClement.com> - 2013-01-22 13:19 -0800
        Re: Initializing a malloc'ed struct whose fields are const with   run-time values William Ahern <william@wilbur.25thandClement.com> - 2013-01-22 13:35 -0800
          Re: Initializing a malloc'ed struct whose fields are const with   run-time values Ian Collins <ian-news@hotmail.com> - 2013-01-23 10:45 +1300
            Re: Initializing a malloc'ed struct whose fields are const with   run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 17:07 -0500
            Re: Initializing a malloc'ed struct whose fields are const with  run-time values Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-22 21:29 -0800
              Re: Initializing a malloc'ed struct whose fields are const with  run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 13:54 +0000
                Re: Initializing a malloc'ed struct whose fields are const with  run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-23 17:08 -0500
                Re: Initializing a malloc'ed struct whose fields are const with    run-time values Ian Collins <ian-news@hotmail.com> - 2013-01-24 11:29 +1300
                Re: Initializing a malloc'ed struct whose fields are const with    run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-23 18:26 -0500
                Re: Initializing a malloc'ed struct whose fields are const with      run-time values Ian Collins <ian-news@hotmail.com> - 2013-01-24 14:03 +1300
                Re: Initializing a malloc'ed struct whose fields are const with      run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-23 23:58 -0500
                Re: Initializing a malloc'ed struct whose fields are const with  run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 23:36 +0000
                Re: Initializing a malloc'ed struct whose fields are const with  run-time values Ian Collins <ian-news@hotmail.com> - 2013-01-24 13:55 +1300
                Re: Initializing a malloc'ed struct whose fields are const with  run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-24 02:44 +0000
                Re: Initializing a malloc'ed struct whose fields are const with  run-time values Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-23 21:39 -0800
                Re: Initializing a malloc'ed struct whose fields are const with  run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-24 00:54 -0500
                Re: Initializing a malloc'ed struct whose fields are const with  run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-24 17:56 +0000
                Re: Initializing a malloc'ed struct whose fields are const with  run-time values Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-24 13:58 -0800
        Re: Initializing a malloc'ed struct whose fields are const with   run-time values James Kuyper <jameskuyper@verizon.net> - 2013-01-22 16:37 -0500
          Re: Initializing a malloc'ed struct whose fields are const with  run-time values Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-22 21:22 -0800
      Re: Initializing a malloc'ed struct whose fields are const with  run-time values Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-22 21:06 -0800
        Re: Initializing a malloc'ed struct whose fields are const with  run-time values Ian Collins <ian-news@hotmail.com> - 2013-01-23 19:55 +1300
          Re: Initializing a malloc'ed struct whose fields are const with  run-time values Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-23 00:48 -0800
            Re: Initializing a malloc'ed struct whose fields are const with  run-time values Ian Collins <ian-news@hotmail.com> - 2013-01-23 23:06 +1300
    Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-22 21:02 +0000
      Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 16:12 -0500
        Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-22 22:37 +0000
          Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 22:29 -0500
            Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 04:28 +0000
              Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-23 00:07 -0500
                Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 14:04 +0000
    Re: Initializing a malloc'ed struct whose fields are const with run-time values Noob <root@localhost> - 2013-01-22 22:10 +0100
  Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-22 21:13 +0000
    Re: Initializing a malloc'ed struct whose fields are const with run-time values Shao Miller <sha0.miller@gmail.com> - 2013-01-22 16:25 -0500
      Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-22 22:21 +0000
    Re: Initializing a malloc'ed struct whose fields are const with run-time values William Ahern <william@wilbur.25thandClement.com> - 2013-01-22 13:32 -0800
      Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 03:50 +0000
    Re: Initializing a malloc'ed struct whose fields are const with run-time values Nick Bowler <nbowler@draconx.ca> - 2013-01-22 21:43 +0000
      Re: Initializing a malloc'ed struct whose fields are const with run-time values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-23 03:45 +0000
        Re: Initializing a malloc'ed struct whose fields are const with run-time values Keith Thompson <kst-u@mib.org> - 2013-01-24 08:23 -0800
  Re: Initializing a malloc'ed struct whose fields are const with run-time values Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-22 20:48 -0800

csiph-web