Quick Q: What's the right way to write Double-Checked Locking in C++11? -- StackOverflow

By Blog Staff | May 9, 2013 01:01 PM | Tags: intermediate basics

Quick A: std::once_flag + std::call_once.

Double-checked locking in C++11?

From the selected answer ([edit] added):

I suggest forgetting about double-checked locking [by hand]. C++ provides a very useful tool for this kind of situation in the form of std::call_once, so use that....

GotW #1 Solution, and GotW #2: Temporary Objects

By Herb Sutter | May 9, 2013 09:52 AM | Tags: None

I've just posted the solution to GotW #1, and problem #2 for discussion. I hope you enjoy them.

GotW #1 Solution: Variable Initialization -- or Is It? (updated for C++11/14)

GotW #2: Temporary Objects

Post-Bristol standards papers mailing available

By Blog Staff | May 9, 2013 08:10 AM | Tags: None

The official post-meeting standards papers mailing is now available. It includes papers adopted at the meeting, updated papers, and updated issues lists.

Please direct discussion to the public std-proposals forum.

Quick Q: How can I make my type construct from { 1, 2, 3, 4 } like vector? -- StackOverflow

By Blog Staff | May 9, 2013 06:56 AM | Tags: basics

Quick A: Write a constructor that takes a std::initializer_list.

See the link for the nice longer answer:

how to implement an initializer list for user defined type? (analogus to std::vector initializer list)

std::vector can be initialized as

 

std::vector<std::string> words1 {"the", "frogurt", "is", "also", "cursed"};
ref

Now if want to achieve the similar functionality for one of my types how do I go about doing it? How should I implement the constructor for this functionality?

New paper: Bristol minutes -- Kyle Kloepper

By Blog Staff | May 8, 2013 07:43 PM | Tags: None

The ISO and U.S. meeting minutes from Bristol are now available.

Document number: N3622, N3623

Date: 2013-05-03

Minutes -- WG21 Meeting No. 55, 15-20 April 2013, Bristol, UK

Minutes -- PL22.16 Meeting No. 60, 15-20 April 2013, Bristol, UK

by Kyle Kloepper

Quick Q: How does return by rvalue reference work? -- StackOverflow

By Blog Staff | May 8, 2013 01:27 PM | Tags: basics

Quick A: So easily that it's automatic... just return a value, not a reference.

How does return by rvalue reference work?

Just when I thought I kind of understand rvalue reference, I ran into this problem. The code is probably unnecessarily long, but the idea is quite simple. There is a main() function, and returnRValueRef() function.

[...]

AClass && returnRValueRef() {
  AClass a1(4);
  return move(a1);
}

int main() {
  AClass a;
  a = returnRValueRef();
}

Quick Q: What's the difference between vector<T...> and vector<T>...? -- StackOverflow

By Blog Staff | May 8, 2013 09:22 AM | Tags: intermediate

SO's version of the question added one layer of wrapping:

What's the difference between doing vector<vector<T...>> and vector<vector<T>...>

I saw code like this earlier:

 

using A = std::vector<std::vector<T>...>

where T is a variadic list of template arguments. I wanted to know what the difference is between putting the parameter pack at the end of the last angle bracket and the first. For example:

using B = std::vector<std::vector<T...>>;

Both of these two compile fine but I don't know what the difference is.

Can someone explain? Thanks.

Introduction To the C++11 Feature: Delegating Constructors -- sumi_cj

By Blog Staff | May 7, 2013 11:35 AM | Tags: basics

Head on over to the C/C++ Cafe for:

Introduction to the C++11 feature: delegating constructors

by sumi_cj

Excerpt:

In C++98, if a class has multiple constructors, these constructors usually perform identical initialization steps before executing individual operations. In the worst scenario, the identical initialization steps are copied and pasted in every constructor. See the following example: ...

Trip Report: ACCU 2013 and the C++ Standards Meeting -- Anthony Williams

By Blog Staff | May 7, 2013 07:41 AM | Tags: None

Anthony Williams just posted another nice trip report on the recent standards meeting in Bristol, as well as a few words on the ACCU conference held back-to-back with the ISO meeting:

ACCU 2013 and the C++ Standards Meeting

by Anthony Williams

 

This year's ACCU conference was at a new venue: the Marriott hotel in Bristol. This is a bit closer to home for me than the previous venue in Oxford, which made the trip there and back more comfortable. As ever, the conference itself was enjoyable, educational and exhausting in equal measure.

 

This year was also BSI's turn to host the Spring ISO C++ committee meeting, which was conveniently arranged to be the week following ACCU, in the same hotel. Having not attended a meeting since the last time the committee met in the UK, I was glad to be able to attend this too. ...

Introduction To the C++11 Feature: Extended friend Declaration -- FangLu

By Blog Staff | May 6, 2013 11:26 PM | Tags: intermediate basics

Head on over to the C/C++ Cafe for:

Introduction to the C++11 feature: extended friend declaration

by FangLu

Excerpt:

The extended friend declaration feature is newly introduced in the C++11 standard. In this article, I will introduce this feature and provide some examples on how to use this feature.

 

Firstly, let's see why this feature is added into C++11. ...