June 16-21, Sofia, Bulgaria
By Blog Staff | Mar 29, 2013 11:09 AM | Tags: intermediate
From SO:
Correct usage of rvalue references as parameters
Let's take the following method as an example: [...]
void Asset::Load( const std::string& Path ) { // complicated method.... } void Asset::Load( std::string&& Path ) { Load(Path); // call the above method }Is this a correct approach to writing rvalue versions of methods?
By Blog Staff | Mar 29, 2013 08:04 AM | Tags: intermediate
From SO:
What's the difference between result_of<F(Args…> and decltype<f(args…)>?
I see that
std::asyncis specified as follows:template <class F, class... Args> // copied out of the standard future<typename result_of<F(Args...)>::type> async(F&& f, Args&&... args);I had expected it to be declared like this:
template <class F, class... Args> auto async(F&& f, Args&&... args) -> future<decltype(f(forward<Args>(args)...)>;Would that be equivalent, or is there some way in which the use of
result_ofis preferable to the use ofdecltype? (I understand thatresult_ofworks with types, whiledecltypeworks with expressions.)
By Blog Staff | Mar 29, 2013 07:37 AM | Tags: None
The Preface for The C++ Programming Language, 4th Ed., is now available on InformIT and also appears in full on this site's Tour of C++ page.
Preface to TC++PL4e
All problems in computer science can be solved by another level of indirection, except for the problem of too many layers of indirection.
-- David J. Wheeler
C++ feels like a new language. That is, I can express my ideas more clearly, more simply, and more directly in C++11 than I could in C++98. Furthermore, the resulting programs are better checked by the compiler and run faster. ...
The use of C++ has changed dramatically over the years and so has the language itself. From the point of view of a programmer, most of the changes have been improvements. The current ISO standard C++ (ISO/IEC 14882:2011, usually called C++11) is simply a far better tool for writing quality software than were previous versions. How is it a better tool? What kinds of programming styles and techniques does modern C++ support? What language and standard-library features support those techniques? What are the basic building blocks of elegant, correct, maintainable, and efficient C++ code? Those are the key questions answered by this book. Many answers are not the same as you would find with 1985, 1995, or 2005 vintage C++: progress happens.
By Blog Staff | Mar 28, 2013 03:47 PM | Tags: experimental
There's a Q&A on StackOverflow, but see also the discussion about this in the March 12 Concepts conference call minutes that were posted here on the same day as the call. It's really more than minutes, it's also a record of discussion that answers this and other questions.
From SO:
What are the differences between concepts and template constraints?
I want to know what are the semantic differences between the C++ full concepts proposal and template constraints (for instance, constraints as appeared in Dlang or the new concepts-lite proposal for C++1y).
What are full-fledged concepts capable of doing than template constraints cannot do?
By Blog Staff | Mar 26, 2013 10:40 PM | Tags: basics
From StackOverflow:
Using smart pointers for class members
I'm having trouble understanding the usage of smart pointers as class members in C++11. I have read a lot about smart pointers and I think I do understand how
unique_ptrandshared_ptr/weak_ptrwork in general. What I don't understand is the real usage. It seems like everybody recommends usingunique_ptras the way to go almost all the time. But how would I implement something like this: ...
By Blog Staff | Mar 25, 2013 03:04 PM | Tags: None
Quick A: It needs it when the container is a vector or similar, because the container may need to grow and reallocate which includes moving or copying the existing contents to the new location.
why does emplace_back need move constructor?
I have the following code... But the
emplace_backdoesn't use the move constructor. Why does the initialization require a move constructor in this instance?
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?