Tuesday, March 15, 2016

Digest for comp.lang.c++@googlegroups.com - 14 updates in 6 topics

ram@zedat.fu-berlin.de (Stefan Ram): Mar 15 11:14PM

> bArray = { false };
>}
>What does the last line of code do?
 
It is ending the compound statement (6.3) that begun with »{«.
 
A compound statement is a statement defined by this production:
 
compound-statement ::= "{" {statement} "}".
 
, it is executed by executing the enclosed statements in the
given order.
Bob Langelaan <bobl0456@gmail.com>: Mar 15 02:05PM -0700

This code compiles on MS VS 2015:
 
#include <array>
int main()
{
std::array<bool, 100> bArray;
bArray = { false };
}
 
What does the last line of code do?
 
Thanks,
Bob
Vir Campestris <vir.campestris@invalid.invalid>: Mar 15 09:15PM

On 15/03/2016 21:05, Bob Langelaan wrote:
> bArray = { false };
> }
 
> What does the last line of code do?
 
Initialises the first element of the array with false.
 
http://en.cppreference.com/w/cpp/container/array
 
and follow the links to
 
http://en.cppreference.com/w/cpp/language/aggregate_initialization
 
HTH
Andy
Marcel Mueller <news.5.maazl@spamgourmet.org>: Mar 15 10:17PM +0100

On 15.03.16 22.05, Bob Langelaan wrote:
> bArray = { false };
> }
 
> What does the last line of code do?
 
Assign a list of one boolean to the array. Due to the fixed nature of
std::array this will in fact clear all elements.
 
 
Marcel
Bob Langelaan <bobl0456@gmail.com>: Mar 15 02:22PM -0700

On Tuesday, March 15, 2016 at 2:17:14 PM UTC-7, Marcel Mueller wrote:
 
> Assign a list of one boolean to the array. Due to the fixed nature of
> std::array this will in fact clear all elements.
 
> Marcel
 
Marcel,
 
Are you saying that the last statement assigns all 100 bool values in bArray to false? I would have thought a loop of some type would have been necessary to accomplish this? Can you expand on the last statement you made? Thanks,
Bob
Bob Langelaan <bobl0456@gmail.com>: Mar 15 02:36PM -0700

On Tuesday, March 15, 2016 at 2:06:11 PM UTC-7, Bob Langelaan wrote:
 
> What does the last line of code do?
 
> Thanks,
> Bob
 
Ok, I modified code to:
 
#include <array>
#include <iostream>
 
int main()
{
std::array<bool, 100> bArray;
bArray = { true };
for (auto x : bArray)
{
std::cout << x << " ";
}
}
 
And I have figured out what is happening by varying whether true or false is assigned or statement is commented out.
 
If assigned false, all 100 bools become false; if assigned true, only the first element becomes true, the remainder become false; if commented out the 100 bools have seemingly random values (memory in bArray is not initialized in other words).
Marcel Mueller <news.5.maazl@spamgourmet.org>: Mar 15 10:49PM +0100

On 15.03.16 22.22, Bob Langelaan wrote:
>> Assign a list of one boolean to the array. Due to the fixed nature of
>> std::array this will in fact clear all elements.
 
> Are you saying that the last statement assigns all 100 bool values in bArray to false?
 
Exactly.
 
> I would have thought a loop of some type would have been necessary to accomplish this? Can you expand on the last statement you made? Thanks,
 
It is a ->"list initializer".
 
And similar to C array assignments trailing elements are initialized to
zero i.e. false.
 
 
Marcel
Gareth Owen <gwowen@googlemail.com>: Mar 15 08:44AM -0600


> std::string object is created for the exception message which can
> cause std::bad_alloc (a std::runtime_error exception) to be thrown
> replacing the originally intended exception.
 
std::bad_alloc is not a runtime_error (needing a string constructor
would be particularly idiotic for bad_alloc), but the point still holds.
 
 
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Gareth Owen <gwowen@googlemail.com>: Mar 15 08:45AM -0600


> Oh, so you mean that the programmer may do something in handling the
> exception to convert logic_error to runtime_error. Sure.
 
No, the problem is
 
throw std::logic_error("I've made a terrible mistake");
 
calls the constructor
 
std::logic_error(const std::string&);
 
which has to construct a string, which might throw std::bad_alloc
 
 
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Bo Persson <bop@gmb.dk>: Mar 15 12:22PM -0600

On 2016-03-15 15:45, Gareth Owen wrote:
 
> calls the constructor
 
> std::logic_error(const std::string&);
 
> which has to construct a string, which might throw std::bad_alloc
 
There is also a constructor
 
explicit logic_error(const char*);
 
which doesn't have to call a string constructor.
 
 
 
Bo Persson
 
 
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woodbrian77@gmail.com: Mar 15 11:28AM -0700

On Tuesday, March 15, 2016 at 12:30:17 PM UTC-5, Bo Persson wrote:
 
> which doesn't have to call a string constructor.
 
> Bo Persson
 
What's the point of std::logic_error? Asserting has
already been defended and I agree with those who say to
use asserts. Recent threads, including this one, have
pointed out dangers and snares associated with
std::logic_error. IMO C++ would be better off without it.
 
Brian
Ebenezer Enterprises
http://webEbenezer.net
Juha Nieminen <nospam@thanks.invalid>: Mar 15 09:03AM

> I think the using approach is clearer than the typedef
> approach. And from a code generator perspective the
> using approach is easier to support.
 
It's still good to understand how typedef works.
 
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Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk>: Mar 15 01:25AM

> On Monday, March 14, 2016 at 3:39:41 AM UTC-5, Alf P. Steinbach wrote:
 
> Alf, please don't swear here.
 
'This video may contain sexual swearwords, I'm afraid. There are 28
'fucks'. Including that one 29. Ah, fuck it, make it 30.' -- Paul Calf
 
https://www.youtube.com/watch?v=42UCpOzTbNU
Chris Vine <chris@cvine--nospam--.freeserve.co.uk>: Mar 15 12:37AM

On Mon, 14 Mar 2016 15:46:11 -0700 (PDT)
 
> I'm sorry, but I don't think the other libraries mentioned
> for C++ serialization options will endure like the the C++
> Middleware Writer.
 
I think this is verging on blasphemy.
 
You would do much better if you refrained from further posting to this
newsgroup until you sort out your personal issues.
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