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Quick Q: Why do I have to std::move a variable that is already a &&? -- StackOverflow

By Blog Staff | Jul 30, 2013 02:09 PM | Tags: basics

Today on SO, a frequently asked question and a nicely summed up answer:

std::move on a variable which already is T&&

On the page http://msdn.microsoft.com/en-us/library/dd293665.aspx Microsoft has an example on how to write a move constructor. It is essentially of the form:

MyClass::MyClass(MyClass&& lhs)
{
    *this = std::move(lhs);
}

I have tried and std::move really is required here, but why? I thought the only thing move did was to convert to T&&. But lhs is already of type MyClass&&, is it not?

Some Notes on C++11 Lambda Functions -- Ranju V.

By Blog Staff | Jul 30, 2013 09:32 AM | Tags: basics

ranjuv.jpgHere's a nice lambda synopsis with some usage notes.

Some notes on C++11 lambda functions

by Ranju V.

From the article:

Bjarne Stroustrup says that C++11, which is the latest ratified revision of the C++ standard, “feels like a new language”.  I think lambda functions are a big part of what makes the language feel so very different from C++03.  Lambda functions basically allow you to do things like this:

vector<int> nums { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
auto evens = count_if(begin(nums), end(nums), [](int num) {
    return (num % 2) == 0;
});

GoingNative day 1 and 2 talks announced

By Blog Staff | Jul 29, 2013 07:30 AM | Tags: None

gn13-1-2.pngGoingNative 2013 will be held on September 4-6. Register soon -- in-room space is limited.

The day 1 and 2 talks have now been posted:

Opening Keynote (Bjarne Stroustrup, Texas A&M University)

Bjarne Stroustrup, creator of C++, will open the show.

C++ Seasoning (Sean Parent, Adobe)

A look at many of the new features in C++ and a couple of old features you may not have known about. With the goal of correctness in mind, we’ll see how to utilize these features to create simple, clear, and beautiful code. Just a little pinch can really spice things up.

Writing Quick Code in C++, Quickly (Andrei Alexandrescu, Facebook)

Contemporary computer architectures make it possible for slow code to work reasonably well. They also make it difficult to write really fast code that exploits the CPU amenities to their fullest. And the smart money is on fast code -- we’re running out of cool things to do with slow code, and the battle will be on doing really interesting and challenging things at the envelope of what the computing fabric endures.

So how to write quick code, quickly? Turns out it’s quite difficult because today’s complex architectures defy simple rules to be applied everywhere. It is not uncommon that innocuous high-level artifacts have a surprisingly high impact on the bottom line of an application’s run time (and power consumed).

This talk is an attempt to set forth a few pieces of tactical advice for writing quick code in C++. Applying these is not guaranteed to produce optimal code, but is likely to put it reasonably within the ballpark.

These tips are based on practical experience but also motivated by the inner workings of modern CPUs.

Don’t Help the Compiler (Stephan T. Lavavej, Microsoft)

C++ has powerful rules for dealing with low-level program structure.  Before a program is ever executed, the compiler determines valuable information about every expression in the source code.  The compiler understands exactly how long each object's resources will be needed (lifetime), whether each expression refers to an object that the program has no other way of accessing (rvalueness), and what operations can be performed on each object (type).  Using examples from C++98 through C++14, this presentation will demonstrate how to write code that works with the compiler's knowledge to increase robustness, efficiency, and clarity.  This presentation will also demonstrate the horrible things that happen when programmers think they can do tasks that are better left to compilers.

Day 1 Panel (all speakers)

Interactive panel. Topic TBD. Attendee-driven Q&A.

Day 2 Keynote: One C++ (Herb Sutter, Microsoft)

Herb Sutter, language architect of Visual C++ and Chairman of the ISO C++ Committee, opens Day 2 with a brand new talk, "One C++."

An Effective C++11/14 Sampler (Scott Meyers)

After years of intensive study (first of C++0x, then of C++11, and most recently of C++14), Scott thinks he finally has a clue. About the effective use of C++11, that is (including C++14 revisions). At last year’s Going Native, Herb Sutter predicted that Scott would produce a new version of Effective C++ in the 2013-14 time frame, and Scott’s working on proving him almost right. Rather than revise Effective C++, Scott decided to write a new book that focuses exclusively on C++11/14: on the things the experts almost always do (or almost always avoid doing) to produce clear, efficient, effective code. In this presentation, Scott will present a taste of the Items he expects to include in Effective C++11/14. If all goes as planned, he’ll also solicit your help in choosing a cover for the book.

C++14: Through the Looking Glass (Michael Wong, IBM)

“The time has come,” the ISO said,
“To talk of many things: 
Of move-capture -- and literals --
Of making lambdas sing --
And why deduction is so hot --
nd if digits should grow wings?”

So have you heard of the next C++ Standard? No, it is not C++11. Even though C++11 has just been ratified, C++14 will likely replace C++11 by next year. By now, we have enough experience with C++11 to know where we are missing various fingers and toes such as:

  • Why do we not have move capture in lambdas? 
  • How about some real user-defined literal suffixes? 
  • Why did we stop with monomorphic lambdas? 
  • If lambda returns can be deduced, why not normal functions? 
  • Could we get digit separators?

C++14 will be more than a bug-fix release, and will contain some important enhancements on top of C++11. It will remove some of the major annoyances from C++11, that we already know of. But more importantly, how will this change the language, library and some important idioms?

The Care and Feeding of C++’s Dragons (Chandler Carruth, Google)

Last year I described C++ as bearing the cautionary label ‘Here Be Dragons.’ And yet we’re all still writing C++ because it is the best programming language for the problems we face. In turn, we need a strategy to deal with the “dragons” that reside in large C++ code bases. The Dragon Book (my old compiler textbook) taught about a collection of tools to address the complexity of compiler design, and while our challenge is somewhat different, the approach remains the same. When a mere mortal programmer ventures forth to battle the complexity of large software systems in C++, they’re going to need some really good tools to help them. At Google, we’ve been building up a platform of such tools. I will introduce the platform and toolset, and show how to use them to write fast and correct C++ code, quickly and correctly.

I will also give a peek into the future of the next generation of tools we’re working on and some of the really interesting changes to C++ that are coming in the next few years to help both programmers and these tools be ever more effective.


Day 2 Panel (all speakers)

Interactive panel. Topic TBD. Attendee-driven Q&A.

Boost Your Productivity with C++11 and Templates (Sep 9-13, Oct 7-11) -- Peter Gottschling

By Blog Staff | Jul 29, 2013 05:11 AM | Tags: intermediate

peter-gottschling.jpgThis course is being held in English and German:

Boost Your Productivity with C++11 and Templates

by Peter Gottschling

  • September 9-13 (German)
  • October 7-11 (English)

Abstract:

Templates (generic programming)

  • Function templates
  • Class templates
  • Variadic Templates (C++11)
  • Concepts
  • Specialization
  • Template arguments that are not types
  • Functors
  • Lambda functions (C++11)

Standard Template Library

  • Iterator concept
  • Containers
  • Functions
  • Meta-programming
  • Let the compiler compute
  • Providing type informations
  • Auto and decltype (C++11)
  • Const-adaptive classes
  • Expression templates

Other advanced and new techniques

  • Calling functions from derived classes without overhead
  • RValues and move semantics (C++11)
  • Initialization lists (C++11)
  • New for-loops (C++11)

Peter Gottschling is author of the Matrix Template Library 4, co-author of the Boost Graph Library and other scientific libraries. He is vice-chair of DIN's programming language group and head of the German delegation in the ISO committee for C++ standardization. He is managing director of SimuNova and taught C++ at TU Dresden, TU Berlin and Indiana University.

Intel Concurrent Collections for C++ 0.9 now supports Xeon Phi on Windows and Linux

By Blog Staff | Jul 29, 2013 01:26 AM | Tags: None

intel.png

Note that some of these concurrent collections are also currently being proposed for ISO standardization.

From the announcement:

Intel Releases New Version of  Intel® Concurrent Collections for C++

Intel released a new version of Intel® Concurrent Collections for C++, a library that helps developers write and tune parallel software. Now with Version 0.9, computers powered by Intel® Xeon Phi™ co-processors are supported and can experience unified programming in the same seamless way that single Intel multi-core workstations and clusters of workstations have experienced with earlier versions. Additionally, its tuning layer was extended, giving developers even easier control over the execution of their application, offering greater potential for performance, scalability and productivity.

Intel Concurrent Collections for C++ is available for Windows and Linux as a free download through the Intel Software Network.

Expression Templates -- Volker Krause

By Blog Staff | Jul 28, 2013 10:29 AM | Tags: advanced

volker-krause.jpgFrom this month's KDE Akademy conference:

Expression Templates: How I Learned to Stop Worrying and Love Template Meta-Programming (30 min video) (slides)

by Volker Krause

The speaker's opening words should be enough to get you to set aside a half hour:

"I'm going to talk about template metaprogramming in general and expression templates in particular. And that's obviously something we use every day. <laughter> You laugh, but in half an hour you will see that we actually do..."

 

Abstract:

Contrary to common perception, expression templates are not bizarre meta-programming theory but something you are (possibly unknowingly) using every day. We'll see what they are good for, how they work and and what to do if they don't.

Originally invented by Todd Veldhuizen for the use in the math library Blitz++, expression templates are often seen as one of those esoteric applications of C++ template meta-programming that results in completely incomprehensible code that only Marc and Thiago understand at best, and that gives you compiler errors longer than an average discussion on the right display manager.

In this talk we will try to counter this (wrong) perception, by looking at why and how this (syntactically) indeed somewhat complex code results in very elegant API and often outperforms conventional implementations. On the way we will see that C++ template meta-programming code is actually not that scary, and that template-related compiler errors aren't that bad either.

Now why would this be of interest to the average Qt or KDE developer? Well, since the introduction of QStringBuilder in Qt 4.7 we have expression templates for a very common use case, string concatenations. And if your code is somewhere in KDE Git, it's very likely Laurent enabled the use of QStringBuilder for you already. So, we are not talking about exotic theory here, but about tools you are using every day.

Is Moving Objects Worth the Hassle? -- Andrew Koenig

By Blog Staff | Jul 26, 2013 11:06 AM | Tags: basics

Koenig's latest just went live at DDJ:

Is Moving Objects Worth the Hassle?

by Andrew Koenig

From the article:

Last week, I discussed how C++ compilers use overloading to decide whether to move or copy an object. This week, I'd like to take a step back and discuss why moving instead of copying is worth doing in the first place.

You might think that this claim needs no justification. After all, copying takes time; so programs that copy a lot of data will be slower than programs that avoid doing so. However, this kind of unthinking optimization can lead to trouble. For example...

New paper: N3705, Agenda and Meeting Notice for WG21 Telecon Meeting -- Herb Sutter

By Blog Staff | Jul 24, 2013 08:45 AM | Tags: None

A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

 

Document number: N3705

Date: 2013-07-23

Agenda and Meeting Notice for WG21 Telecon Meeting

by Herb Sutter

Excerpt:

Note: As discussed at the previous telecon and in committee email, this telecon is being held one week before the face-to-face meeting, rather than two weeks, to avoid holidays and other conflicts.

The Universal Reference/Overloading Collision Conundrum -- Scott Meyers

By NoSenseEtAl | Jul 24, 2013 07:22 AM | Tags: intermediate

meyers-nwcpp-13.PNG[Blog suggestion by NoSenseEtAl. Text below added by editor.]

Scott Meyers gave a well-received "beta" talk last week at NWCPP on the topic below, which he described as the most complex Item he's encountered as he prepares his upcoming book Effective C++11/14:

The Universal Reference/Overloading Collision Conundrum

by Scott Meyers

Abstract:

To help address the confusion that arises when rvalue references become lvalue references through reference collapsing, Scott Meyers introduced the notion of "universal references." In this presentation, he builds on this foundation by explaining that overloading functions on rvalue references is sensible and useful, while seemingly similar overloading on universal references yields confusing, unhelpful behavior. But what do you do when you want to write a perfect forwarding function (which requires universal references), yet you want to customize its behavior for certain types? If overloading is off the table, what's on? In this talk, Scott surveys a variety of options.

Though Scott will give a one-slide overview of the idea behind universal references at the beginning of the presentation, attendees are encouraged to familiarize themselves with the notion in more detail prior to the talk. Links to written and video introductions to universal references are available here.