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By Blog Staff | Mar 25, 2013 11:08 AM | Tags: None
C++11 support is already available by default in many environments and platforms, but as it reaches new ones you may still need to turn it on explicitly. Android is an example:
Enable C++11 support on Android
How do I integrate C++11 in Android in order to use
unordered_map(the new version ofhash_map)?
By Blog Staff | Mar 25, 2013 10:01 AM | Tags: None
Quick A: No, only the ones you actually use.
From StackOverflow:
Does [=] imply that all local variables will be copied?
When I write a lambda with
[=], does it mean that all my local variables will be copied into members of the created struct or can I assume that only those will that are actually used in the lambda?
By Blog Staff | Mar 19, 2013 10:52 AM | Tags: intermediate experimental
[Ed.: We're calling particular attention to this paper as of broad interest to the community, although still undergoing standardization. This is one of the major papers being considered at the upcoming Bristol standards meeting in April for near-term standardization work.]
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: N3580
Date: 2013-03-17
Concepts Lite: Constraining Templates with Predicates
by Andrew Sutton, Bjarne Stroustrup, Gabriel Dos Reis
Excerpt:
In this paper, we introduce template constraints (a.k.a., “concepts lite”), an extension of C++ that allows the use of predicates to constrain template arguments. The proposed feature is minimal, principled, and uncomplicated. Template constraints are applied to enforce the correctness of template use, not the correctness of template definitions. The design of these features is intended to support easy and incremental adoption by users. More precisely, constraints:
- allow programmers to directly state the requirements of a set of template arguments as part of a template’s interface,
- support function overloading and class template specialization based on constraints,
- fundamentally improve diagnostics by checking template arguments in terms of stated intent at the point of use, and
- do all of this without any runtime overhead or longer compilation times.
This work is implemented as a branch of GCC-4.8 and is available for download at http://concepts.axiomatics.org/˜ans/. The implementation includes a compiler and a modified standard library that includes constraints. Note that, as of the time of writing, all major features described in this report have been implemented.
This paper is organized like this:
- Tutorial: introduces the basic notions of constraints, shows examples of their use, and gives examples of how to define constraints.
- Discussion: explains what constrains are not. In particular, we try to outline constraints’s relation to concepts and to dispel some common misconceptions about concepts.
- User’s guide: provides many more tutorial examples and demonstrate the completeness of the constraints mechanism.
- Implementation: gives an overview of our GCC compiler support for constraints.
- Extensions: we discuss how constraints might be extended to interact with other proposed features.
- Language definition: presents a semi-formal definition of constraints.
By Blog Staff | Mar 19, 2013 09:11 AM | Tags: basics
There are many reasons to love the now-standard std::unique_ptr and std::shared_ptr. They're well summarized in this classic on StackOverflow.
You don't often see a SO question with 185 upvotes, 117 favorites, and 269 upvotes on the selected answer. Here's one:
What is a smart pointer and when should I use one?
By Blog Staff | Mar 18, 2013 02:06 PM | Tags: basics
Quick A: No reason, varargs are type-unsafe and entirely superseded by C++11 features (unless you need C compatibility).
Why use variadic arguments now when initializer lists are available?
I've been wondering what are the advantages of variadic arguments over initializer lists. Both offer the same ability -- to pass indefinite number of arguments to a function.
What I personally think is initializer lists are a little more elegant. Syntax is less awkward.
Also, it appears that initializer lists have significantly better performance as the number of arguments grows.
So what am I missing, besides the possibility to use use variadic arguments in C as well?
By Blog Staff | Mar 14, 2013 03:05 PM | Tags: intermediate
Andrzej continues with a third installment in his series on preconditions.
Preconditions, Part 3
by Andrzej Krzemieński
In this post, I examine a couple of cases and try to answer the question when and how to specify preconditions, and when it is better not to do it. I believe it gives a deeper insight into the nature of preconditions.
By Blog Staff | Mar 14, 2013 02:31 PM | Tags: intermediate
Ed.: Most standardization papers are about technical changes. It's not often you get a tutorial written by a world-class expert submitted as a WG21 paper. Thanks, Walter!
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: N3551
Date: 2013-03-12
Random Number Generation in C++11
by Walter Brown
Excerpt:
For programmers seeking to familiarize themselves with the
<random>component of the
C++11 standard library, we provide background information and tutorial guidance with numerous
usage examples.1 Introduction 1
2 Getting started 2
3 An anti-pattern 3
4 Initializing an engine 3
5 What else can an engine do? 4
6 Engines in the standard library 5
7 Sharing an engine 5
8 Distributions in the standard library 6
9 What else can a distribution do? 8
10 A simple toolkit 9
11 A final example 9
12 Caveat lector! 10
13 What’s next? 11
14 Acknowledgments 11
15 Bibliography 11
16 Revision history 12
By Blog Staff | Mar 12, 2013 11:49 AM | Tags: intermediate
Quick A: Because exceptions occur (or not) dynamically.
Why is C++0x's
noexceptchecked dynamically?I am curious about the rationale behind noexcept in the C++0x FCD.
throw(X)was [deprecated], butnoexceptseems to do the same thing. Is there a reason thatnoexceptisn't checked at compile time? It seems that it would be better if these functions were checked statically that they only dcalled throwing functions within atryblock.
By Blog Staff | Mar 12, 2013 04:45 AM | Tags: basics
Quick A: When correctly implemented per the standard, you get in-place construction with perfect forwarding.
Longer question:
push_back vs emplace_back
I'm a bit confused regarding the difference between push_back and emplace_back.
void emplace_back(Type&& _Val); void push_back(const Type& _Val); void push_back(Type&& _Val);As there is a push_back overload taking a rvalue reference I don't quite see what the purpose of emplace_back becomes?
By Blog Staff | Mar 11, 2013 04:53 PM | Tags: intermediate
Quick A: A lot. They can bind to anything callable, not just functions. And they can perform conversions on parameter and return types.
Is there a use case for std::function that is not covered by function pointers, or is it just syntactic sugar?
The notation for
std::functionis quite nice when compared to function pointers. However, other than that, I can't find a use case where it couldn't be replaced by pointers. So is it just syntactic sugar for function pointers?