Wednesday, March 16, 2016

Digest for comp.lang.c++@googlegroups.com - 9 updates in 5 topics

"Öö Tiib" <ootiib@hot.ee>: Mar 16 04:03PM -0700

On Wednesday, 16 March 2016 19:23:51 UTC+2, Bob Langelaan wrote:
 
> > Yes, it is aggregate so when initialized it will be default-initialized
> > (so falses) to end and when not initialized then it will be uninitialized.
 
> But in my mind an entity can only be "initialized" when it is defined.
 
Yes, perhaps bad wording of mine.
 
 
> does not initialize bArray because bArray was previously defined.
 
> I am assuming that what is happening that the { false } value on the right of the assignment statement is being converted to a temporary std::array<bool, 100> object which is initialized to { false }. This temporary object is then assigned to bArray.
 
> Is my assumption correct?
 
Yes, the '{ false }' is of magic C++11 type 'std::initializer_list'.
Converted from it is a temporary object of type 'std::array<bool, 100>'
The "conversion" is same as initialization as aggregate and then it
is assigned to 'bArray'. Actually compiler likely optimizes all the
temporaries out.
Bob Langelaan <bobl0456@gmail.com>: Mar 16 04:13PM -0700

On Wednesday, March 16, 2016 at 4:04:00 PM UTC-7, Öö Tiib wrote:
> The "conversion" is same as initialization as aggregate and then it
> is assigned to 'bArray'. Actually compiler likely optimizes all the
> temporaries out.
 
Thanks! I think I have it now :)
"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Mar 16 08:47PM +0100

On 16.03.2016 01:27, JiiPee wrote:
> Is it possible to get a behaviour of "inherited" enum?
 
Not quite, because with a values type the Is-A relationship goes the
other way than with class inheritance, which is what you have in C++.
 
For example, a rational number is the result of dividing one integer by
another with ordinary division, like 3/4. The set of rationals includes
the set of integers, like the set of animals includes the set of dogs,
so an integer Is-A rational, like a dog Is-An animal. But it makes sense
in C++ to have an Animal base class and a Dog derived class, because the
Dog class /adds/ information and behavior, while it does not make sense
in C++ to have a Rational base class and an Integer derived class,
because the Rational class has more information (you need two integers
to describe a rational, in general): it's ungood base.
 
Generally the kind of relationship involved for Rational and Integer is
modeled (or implemented) by value conversion, while the kind of
relationship for Animal and Dog is modeled by reference conversion.
 
But a typed enumeration is not a class, so the value conversion
technique isn't applicable.
 
This leaves us with no proper tools to apply, and so it's all about
choosing some suitable compromise – slightly deficient one way or another...
 
 
 
> So how to dynamically add elements to an enum or simulate it somehow so
> that when adding a new class I do not need to touch the original enum
> definition but I can add the type inside the new class.
 
Instead of these integer identifiers you can probably use typeid.
 
 
> create integer constants for each animal type in each class, but then
> they would be integer type which is "weak"... I would like to have
> something similar to enum or class-type.
 
The only practical way I can see is declare the enum type centrally,
with values for all possible types.
 
 
Cheers!,
 
- Alf
Christopher Pisz <nospam@notanaddress.com>: Mar 16 05:59PM -0500

On 3/15/2016 7:42 PM, Stefan Ram wrote:
 
> Now to add another animal »cat«, you just add
> »cat.h« and run the make process. The script will
> generate the new »all_animals.h«.
 
I didn't realize grep was part of C++
Yuck!
 
 
--
I have chosen to troll filter/ignore all subthreads containing the
words: "Rick C. Hodgins", "Flibble", and "Islam"
So, I won't be able to see or respond to any such messages
---
woodbrian77@gmail.com: Mar 16 03:49PM -0700

> meeting this weekend.
 
> http://www.aojs.org/
 
> They have existed for over 60 years.
 
I'm blessed today to learn of a parallel organization
also on American soil --
 
Sinai and Synapses
 
http://sinaiandsynapses.org/
 
Their Mission
 
Sinai and Synapses offers people a worldview that is
both scientifically grounded and spiritually uplifting.
It provides tools and language for learning and living
to the millions of people who see science as their ally
as they pursue personal growth and the repair of our world.
 
Through classes, seminars, lectures, videos and writings,
it helps create a vision of religion that embraces critical
thinking and scientific inquiry, and at the same time,
gives meaning to people's lives and helps them make a
positive impact on society.
 
It is incubated at Clal - The National Jewish Center for
Learning and Leadership, which links Jewish wisdom with
innovative scholarship to deepen civic and spiritual
participation in American life.
 
Their Methods
 
Sinai and Synapses explores big questions from both religious
and scientific perspectives, and achieves its mission through
several programs, activities, and learning opportunities.
 
Adult education classes, with courses such as "There Are
Places I Remember: How Memory Works (And How It Doesn't),"
"This is Your Brain on Judaism," "Faith in a Scientific Age,"
and "The Morality Stereo System: Why Liberals and
Conservatives Can't Seem to Listen to Each Other."
 
Seminars for our Sinai and Synapses Fellows, bringing
together clergy and scientists to learn together from
the top scholars in both the religious and scientific
worlds, and then to create programs and facilitate
discussions on topics such as "Are We Using Technology,
or Is Technology Using Us?"
 
-----------------------------------------------------------
 
This is great news.
 
 
Brian
Ebenezer Enterprises - In G-d we trust.
http://webEbenezer.net
ram@zedat.fu-berlin.de (Stefan Ram): Mar 16 10:40PM

>1. Design an algorithm to print hello world to the screen.
 
|
|
|
v
.----------
/ print /
/ "h" /
/ /
-----------
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v
.----------
/ print /
/ "e" /
/ /
-----------
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v
.----------
/ print /
/ "l" /
/ /
-----------
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v
.----------
/ print /
/ "l" /
/ /
-----------
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v
.----------
/ print /
/ "o" /
/ /
-----------
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v
.----------
/ print /
/ " " /
/ /
-----------
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v
.----------
/ print /
/ "w" /
/ /
-----------
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v
.----------
/ print /
/ "o" /
/ /
-----------
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v
.----------
/ print /
/ "r" /
/ /
-----------
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v
.----------
/ print /
/ "l" /
/ /
-----------
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v
.----------
/ print /
/ "d" /
/ /
-----------
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v
.----------
/ print /
/ " " /
/ /
-----------
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v
.----------
/ print /
/ "t" /
/ /
-----------
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v
.----------
/ print /
/ "o" /
/ /
-----------
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v
.----------
/ print /
/ " " /
/ /
-----------
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v
.----------
/ print /
/ "t" /
/ /
-----------
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v
.----------
/ print /
/ "h" /
/ /
-----------
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v
.----------
/ print /
/ "e" /
/ /
-----------
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v
.----------
/ print /
/ " " /
/ /
-----------
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v
.----------
/ print /
/ "s" /
/ /
-----------
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v
.----------
/ print /
/ "c" /
/ /
-----------
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v
.----------
/ print /
/ "r" /
/ /
-----------
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v
.----------
/ print /
/ "e" /
/ /
-----------
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v
.----------
/ print /
/ "e" /
/ /
-----------
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v
.----------
/ print /
/ "n" /
/ /
-----------
 
>a. Write pseudo code of your solution first. (10 pts)
 
Dear Computer, do me a favor and please print this letter: "h"! Thank you!
Dear Computer, do me a favor and please print this letter: "e"! Thank you!
Dear Computer, do me a favor and please print this letter: "l"! Thank you!
Dear Computer, do me a favor and please print this letter: "l"! Thank you!
Dear Computer, do me a favor and please print this letter: "o"! Thank you!
Dear Computer, do me a favor and please print this letter: " "! Thank you!
Dear Computer, do me a favor and please print this letter: "w"! Thank you!
Dear Computer, do me a favor and please print this letter: "o"! Thank you!
Dear Computer, do me a favor and please print this letter: "r"! Thank you!
Dear Computer, do me a favor and please print this letter: "l"! Thank you!
Dear Computer, do me a favor and please print this letter: "d"! Thank you!
Dear Computer, do me a favor and please print this letter: " "! Thank you!
Dear Computer, do me a favor and please print this letter: "t"! Thank you!
Dear Computer, do me a favor and please print this letter: "o"! Thank you!
Dear Computer, do me a favor and please print this letter: " "! Thank you!
Dear Computer, do me a favor and please print this letter: "t"! Thank you!
Dear Computer, do me a favor and please print this letter: "h"! Thank you!
Dear Computer, do me a favor and please print this letter: "e"! Thank you!
Dear Computer, do me a favor and please print this letter: " "! Thank you!
Dear Computer, do me a favor and please print this letter: "s"! Thank you!
Dear Computer, do me a favor and please print this letter: "c"! Thank you!
Dear Computer, do me a favor and please print this letter: "r"! Thank you!
Dear Computer, do me a favor and please print this letter: "e"! Thank you!
Dear Computer, do me a favor and please print this letter: "e"! Thank you!
Dear Computer, do me a favor and please print this letter: "n"! Thank you!
 
>b. Write the c code for your solution. (20 pts)
 
putchar( 'h' );
putchar( 'e' );
putchar( 'l' );
putchar( 'l' );
putchar( 'o' );
putchar( ' ' );
putchar( 'w' );
putchar( 'o' );
putchar( 'r' );
putchar( 'l' );
putchar( 'd' );
putchar( ' ' );
putchar( 't' );
putchar( 'o' );
putchar( ' ' );
putchar( 't' );
putchar( 'h' );
putchar( 'e' );
putchar( ' ' );
putchar( 's' );
putchar( 'c' );
putchar( 'r' );
putchar( 'e' );
putchar( 'e' );
putchar( 'n' );
 
>2. Design an algorithm that takes an integer value from the user and notifies the user either this number is even or odd.
 
.-------------------------------------------------------------------------.
| take an integer value from the user |
'-------------------------------------------------------------------------'
|
|
v
.-------------------------------------------------------------------------.
| notify the user either this number is even or odd |
'-------------------------------------------------------------------------'
 
>a. Write pseudo code of your solution first. (20 pts)
 
Take an integer value from the user and then
notify the user either this number is even or odd.
 
 
>b. Write the c code for your solution. (20 pts)
 
take_an_integer_value_from_the_user();
notify_the_user_either_this_number_is_even_or_odd();
 
>3. (30pts) Write the c code of the algorithm given in the slide 18 of 03.ppt.
 
#include <stdio.h>
 
int main( void )
{ struct s { char * val; struct s * next; }a={ "alpha", &a };
printf( "%s\n", a.val );
printf( "%s\n", a.next->val );
printf( "%s\n", a.next->next->val );
printf( "%s\n", a.next->next->next->val ); }
ram@zedat.fu-berlin.de (Stefan Ram): Mar 16 10:44PM

>program; no diagnostic required."
 
>I suspect taking the address of a function qualifies as odr-use, so the
>above program indeed contains UB.
 
Thank you! I now have modified this teaching example of mine so as to
include the definition:
 
#include <iostream> /* ::std::cout */
#include <ostream> /* << */
#include <string> /* ::std::string */
 
using namespace ::std::literals;
 
::std::string s() {} /* this line was added 2016-03-16 */
 
int main() { ::std::string const s(); ::std::cout << '>' << s << "<\n"s; }
Paavo Helde <myfirstname@osa.pri.ee>: Mar 16 09:20PM +0200

On 16.03.2016 4:41, Stefan Ram wrote:
 
> The above program prints »1« here.
 
> Does the above program have undefined behavior because the
> function »s« is just being declared but not defined anywhere?
 
From the standard: "Every program shall contain exactly one definition
of every non-inline function or variable that is odr-used in that
program; no diagnostic required."
 
I suspect taking the address of a function qualifies as odr-use, so the
above program indeed contains UB.
legalize+jeeves@mail.xmission.com (Richard): Mar 16 10:19PM

[Please do not mail me a copy of your followup]
 
Paavo Helde <myfirstname@osa.pri.ee> spake the secret code
>program; no diagnostic required."
 
>I suspect taking the address of a function qualifies as odr-use, so the
>above program indeed contains UB.
 
[3.2 basic.def.odr]
 
3. "[...] A function whose name appears as a potentially-evaluated
expression is odr-used if it is the unique lookup result or the selected
member of a set of overloaded functions (3.4, 13.3, 13.4), unless it is
a pure virtual function and its name is not explicitly qualified."
 
Seems pretty straight-forward to me that this means that using the
name of a function as a void* argument to operator<< is an odr-use of
the name.
--
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The Computer Graphics Museum <http://computergraphicsmuseum.org>
The Terminals Wiki <http://terminals.classiccmp.org>
Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com>
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