March 19-21, Madrid, Spain
April 1-4, Bristol, UK
June 16-21, Sofia, Bulgaria
By Blog Staff | Dec 24, 2012 05:40 PM | Tags: intermediate
From StackOverflow [c++11]:
I have an object that needs to take a variadic argument list in its constructor and store the arguments in a
vector. How do I initialize avectorfrom a the arguments of a variadic constructor?class GenericNode { public: GenericNode(GenericNode*... inputs) { /* Something like... */ // inputs_.push_back(inputs)...; } private: std::vector<GenericNode*> inputs_; };
By Blog Staff | Dec 24, 2012 10:04 AM | Tags: None
As we're all unwinding at the end of the year, your blog staff would like to recommend watching again one of the year's most hilariously entertaining and deeply informative talks about the world's hottest new C++ compiler -- a holiday video that's genuinely fun:
Clang: Defending C++ from Murphy's Million Monkeys
by Chandler Carruth
at GoingNative 2012[... Clang] provides fantastic diagnostics, static and dynamic program analysis, advanced rewriting and refactoring functionality, and language extensibility. Together with improvements to the language in C++11 these help programmers cope with today's code and write better code tomorrow. Clang also makes it easier than ever before to evolve and evaluate new language features and extensions to make C++ itself better.
Through this talk I'll give some background on the Clang compiler, what it does today to make writing C++ better, and how we're using it to help shape the C++ language going forward.
Even your non-technical family and friends will probably enjoy the first five minutes.
Thanks again to Chandler, GoingNative, and Channel 9 for an engaging and illuminating presentation.
By Blog Staff | Dec 22, 2012 04:27 PM | Tags: None
Chris Lattner has announced the release of version 3.2 of the Clang C++ compiler, as part of LLVM 3.2. Read the release notes here.
Highlights include:
_Alignof supportBy Blog Staff | Dec 21, 2012 02:27 PM | Tags: basics
From StackOverflow [c++11]:
Consider the following code:
unordered_set<T> S = ...; for (const auto& x : S) if (...) S.insert(...);This is broken correct? If we insert something into
Sthen the iterators may be invalidated (due to a rehash), which will break the range-for because under the hood it is usingS.begin...S.end.
Is there some pattern to deal with this?
By Joel Lamotte | Dec 21, 2012 01:24 PM | Tags: intermediate
For your Friday viewing pleasure, from the always-engaging master, Andrei Alexandrescu:
Three Optimization Tips for C++ (video) (PDF slides)
Andrei Alexandrescu
Facebook NYC, December 4, 2012
From an early slide in the talk: "Intuition:
- Ignores aspects of a complex reality
- Makes narrow/wrong/obsolete assumptions
[...]
- The only good intuition: "I should time this."
Enjoy.
(Bonus: The tips are also applicable in other languages. They just happen to be easier to use and control in C++.)
By Blog Staff | Dec 20, 2012 06:15 PM | Tags: experimental
This week, Faisal Vali shared an initial "alpha" implementation of generic lambdas in Clang. Faisal is the lead author of the proposal (N3418), with Herb Sutter and Dave Abrahams.
To read and participate in the active discussion, see the message thread on std-proposals.
Here is a copy of Faisal's announcement:
Motivated by the positive feedback we received regarding Generic Lambdas (during the October 2012 ISO C++ Standards Meeting in Portland), I have implemented a reasonably complete (unless I am missing something obvious) implementation (http://faisalv.github.com/clang-glambda/) of most of the proposal (named lambda syntax for functions has not been attempted) using a fork of Clang.
We would like to encourage developers who are interested in this feature, to either compile the code or download the binaries (sorry, only Windows for now) and play with the implementation and provide us with feedback so that we can incorporate it within our next revision of the document.
The following link: http://faisalv.github.com/clang-glambda/, has some instructions (towards the bottom) on how to compile the code or use the binaries for Windows.
Any and all constructive feedback will be greatly appreciated.
The current version (12/2012) implements subproposals 2.1, 2.2, 2.3 and 2.5.
2.1 Allow the type-specifier within a parameter declaration of a lambda to be
auto(i.e.autois mandatory)auto Sum = [](auto a, decltype(a) b) { return a + b; }; int i = Sum(3, 4); double d = Sum(3.14, 2.77);
2.2 Allow the use of familiar template syntax in lambda expressions
auto NumElements = []<int N>(auto (&a)[N]) { return N; }; int arri[]{1, 2, 3}; double arrd[]{3.14, 2.77, 6.626}; auto total = NumElements(arri) + NumElements(arrd);
2.3 Permit a lambda body to be an expression
int local = 10; auto L = [&](auto a) a + ++local;
2.5 Autogenerate a conversion to function pointer in captureless generic lambdas
auto L = [](auto a, decltype(a) b) { return a + b; }; int (*fp)(int, int) = L;
Thank you and looking forward to the feedback!
By Joel Lamotte | Dec 20, 2012 09:09 AM | Tags: basics
Here is a question from Programmer's StackExchange (tags [c++] and [c++11]) which most C++ developers, whatever their level, will ask as soon as they are introduced to the new Uniform Initialization syntax:
Is it recommended now to use uniform initialization in all cases? What should the general approach be for this new feature as far as coding style goes and general usage? What are some reasons to not use it?
The accepted answer clearly provides very good reasons to use this new syntax as much as possible (if your compiler supports it already): minimizing redundant typenames and avoiding the Most Vexing Parse. It also points some reasons to not use this syntax, in particular in case you're trying to call a standard container constructor.
There is one other reason not to:
std::vector<int> v{100};What does this do? It could create a
vector<int>with one hundred default-constructed items. Or it could create avector<int>with one item whose value is100. ... In actuality, it does the latter.
Read the full QA.
By Blog Staff | Dec 17, 2012 09:01 AM | Tags: basics
Last Monday, Bjarne Stroustrup gave a live interview to David Intersimone of Embarcadero to kick off their CodeRage 7 conference. Bjarne discusss the new Standard C++ Foundation, the ISO C++11 standard, new language features, how C++11 builds on C++’s strengths, application portability, and C++’s ubiquitous presence in the markets.
The video is now on YouTube. Enjoy.
By Blog Staff | Dec 17, 2012 08:02 AM | Tags: advanced
On using constexpr and unions, with insights into the design of the currently-proposed std::optional<T>:
Constexpr Unions
by Andrzej Krzemieński
I assume you are already familiar with
constexprfunctions. (If not, see a short introduction here.) [Ed.: We linked to that article recently, so you've seen it if you've been following isocpp.org.]In this post I wanted to share my experience with using unions in constant expressions. Unions are not very popular due to type-safety hole they open, but they offer some capabilities that I found priceless when working with Fernando Cacciola on
std::optionalproposal.
By Blog Staff | Dec 16, 2012 12:55 PM | Tags: basics
To help balance out "introductory," "intermediate," and "advanced" content, we're trying an experiment to highlight interesting bite-sized tidbits that are in the first two categories.
Here's today's tidbit from StackOverflow's [c++11] tag:
The declaration for the
[]operator on astd::mapis this:T& operator[] ( const key_type& x );Is there a reason it isn't this?
T& operator[] ( const key_type& x ); const T& operator[] const ( const key_type& x );Because that would be incredibly useful any time you need to access a member map in a
constmethod.
As the two top answers show, the answer is different in C++98 and C++11, and C++11 is where it's "at" (pardon).