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By Blog Staff | Jun 13, 2014 03:10 AM | Tags: basics
Quick A: Yes. Otherwise, it would be unsafe and a lot less unique.
From SO:
Is
unique_ptrguaranteed to storenullptrafter move?std::unique_ptr<int> p1{new int{23}}; std::unique_ptr<int> p2{std::move(p1)}; assert(!p1); // is this always true?
By Marco Arena | Jun 9, 2014 12:29 PM | Tags: experimental advanced
Paolo Severini expands the concept of resumable functions to support generator functions, providing the ability of lazily producing the values in a sequence only when they are needed.
Generator functions in C++
by Paolo Severini
From the article:
In the previous post we had a look at the proposal of introducing resumable functions into the C++ standard to support writing asynchronous code modeled on the C# async/await pattern.
We saw that it is already possible to experiment with the future
resumableandawaitkeywords in Visual Studio, by installing the latest November 2013 CTP. But the concept of resumable functions is not limited to asynchrony; in this post we’ll see how it can be expanded to support generator functions.Generator functions and lazy evaluation
In several languages, like C# and Python, generator functions provide the ability of lazily producing the values in a sequence only when they are needed. ...
By Blog Staff | Jun 9, 2014 12:02 PM | Tags: boost advanced
Here's an experience report about using Boost's graph support in an existing game app, with some notes about Boost Concepts:
Masking a Class in Boost Graph. Part 1: Let the Interface Be
Masking a Class in Boost Graph. Part 2: Completing the Implementation of Concept Support
by Vadim Androsov
From the articles:
I had to rebuild a pathfinding algorithm for our game recently. The previous one (Boost Concepts) was bad as any sidestep was dangerous. So I wanted to take a ready algorithm from a good source. That’s exactly when I remembered about boost as there’s functionality for working with graphs. Unfortunately “find a function, call it and everything will work” approach wasn’t meant to be realized. The library is focused on the maximum use flexibility which has badly affected its simplicity. But it’s better than creating it from scratch (then fixing it). I didn’t want to bother with other libraries, while boost has already been used in the project. ...
By Blog Staff | Jun 6, 2014 06:50 AM | Tags: None
Recently added to Bjarne Stroustrup's FAQ:
Are lists evil?
by Bjarne Stroustrup
From the FAQ:
According to some corners of the Web, I am under the impression that vectors are always better than linked lists and that I don't know about other data structures, such as trees (e.g.
std::set) and hash tables (e.g.,std::unordered_map). Obviously, that's absurd.The problem seems to be an interesting little exercise that John Bentley once proposed to me: Insert a sequence of random integers into a sorted sequence, then remove those elements one by one as determined by a random sequece of positions: Do you use a vector (a contiguously allocated sequence of elements) or a linked list? For example, see Software Development for Infrastructure. I use this example to illustrate some points, encourage thought about algorithms, data structures, and machine architecture, concluding:
- don't store data unnecessarily,
- keep data compact, and
- access memory in a predictable manner.
Note the absence of "list" and "vector" in the conclusion. Please don't confuse an example with what the example is meant to illustrate.
I used that example in several talks, notably:
This video has been popular: It has been downloaded more than 250K times (plus another 50K+ times at verious other sites). My impression is that many viewers failed to understand that the purpose of that example is to illustrate some general principles and to make people think. Initially, most people say ``List of course!'' (I have tried asking that question many times) because of the many insertions and deletions ``in the middle'' (lists are good at that). That answer is completely and dramatically wrong, so it is good to know why.
I have been using the example for years, and had graduate students implement and measure dozens of variants of this exercise and different exercises. Examples and measurements by others can be found on the Web. Of course,
- I have tried maps (they are much better than lists, but still slower than vectors)
- I have tried much larger elements sizes (eventually lists come into their own)
- I have used binary search and direct insertion for vectors (yes, they speed up even further)
- I checked my theory (no I'm not violating any big-O complexity rule; it is just that some operations can be dramatically more expensive for one data structure compared to another)
- I have preallocated links (that's better than
std::listbut the traversal still kills performance)- I have used singly-linked lists,
forward_lists, (that doesn't make much difference, but makes it a bit harder to ensure that the user code is 100% equivalent)- I know (and say) that 500K lists are not common (but that doesn't matter for my main point). We use many structures (large and small) where there is a choice between linked and contiguous reprentation.
- I know that for insertion
push_front()is faster forstd::lists andpush_back()s is faster forvectors. You can construct examples to illustrate that, but this example is not one of those.My point is not about lists as such. They have their uses, but this example isn't one of them. Please don't confuse the example with what the example is used to illustrate. This example is about use of memory: We very often create a data structure, do some computation on it requiring access (often, traversal), and then delete it. The ordered sequence is simply an example of such use and the example is presented to get people to think about what matters in such cases. My suggestion is:
- don't store data unnecessarily,
- keep data compact, and
- access memory in a predictable manner.
I emphasize the importance of cache effects. In my experience, all but true experts tend to forget those when algorithms are discussed.
And, yes, my recomendation is to use
std::vectorby default. More generally, use a contiguous representation unless there is a good reason not to. Like C, C++ is designed to do that by default.Also, please don't make statements about performance without measurements. I have seen a case where changing a zero-to-two-element list to a zero-to-two-element vector made a factor-of-two difference to an algorithm. I didn't expect that. Nor did other experts looking at the code.
By Blog Staff | Jun 3, 2014 11:18 AM | Tags: intermediate concurrency
Fresh on Kukuruku:
Lightweight HTTP Server in less than 40 Lines on libevent and C++11
by NYM
From the article:
Looking through programming articles sometimes I see posts about creating your own HTTP server. I am most interested in C++ so I often read blogs about it. After looking them through you could easily write you own web server “on sockets” using boost.asio or something else. I also examined libevent and libev. Each of them has its advantages. Libevent is of great interest to me for developing a small HTTP server. Considering some innovations in C++11 the code becomes much more space-efficient and allows for the creation of a basic HTTP server in less than 40 lines.
By Blog Staff | Jun 3, 2014 06:40 AM | Tags: intermediate
The latest from the desk of Andrzej:
Ref-qualifiers
by Andrzej Krzemieński
From the article:
In this post I want to describe a small language feature added in C++11 that, although essential for full value semantics support, is often neglected in tutorials and in compiler implementations....
By Blog Staff | Jun 3, 2014 05:39 AM | Tags: None
Overload 121 is now available. It contains the following C++-related articles, and more:
CONSTANTS often shout. Jonathan Wakely considers why this happens in C and what the alternatives are in C++.
Using multiple interfaces can slow things down. Daniel Gutson and Pablo Oliva present an alternative.
By Fernando Pelliccioni | May 28, 2014 07:32 PM | Tags: intermediate
[Ed: Note that this article series is not (yet) about C++ code, but it promises to go there and it has an interesting pedigree in its generic programming design analysis (Alex Stepanov) and reviewers (several ISO C++ participants including Andrzej Krzemienski and Dean Michael Berris.]
Writing min function, part 1: The rise of Concepts
by Fernando Pelliccioni
From the article:
This is the first in a series of articles in which I want to transmit what I learned (or what I think I learned) from the books, papers, lectures of Alexander Stepanov.
These are the lessons that Alex gives us, and I want to show them in this series:
- Specify our algorithms correctly
- Programming must be based on a solid mathematical foundation
- Designing our API’s consistently
- Not always the library implementations provided by the programming languages we use are correct, even though they are designed by “experts”.
- The concept of Stability
- Generic programming, of course!
By Blog Staff | May 28, 2014 07:23 PM | Tags: intermediate basics
Today on Kukuruku:
Ref-qualified member functions
by Alexander Kulikov
From the article:
Today I’m going to tell you about a new and a little known (to my mind) C++ feature — reference-qualified member functions. I’ll tell about the rules of such functions overloading and, as an example of use, I’ll show you that with the help of ref-qualified you can try to improve the resource management scheme, which is implemented with the help of another C++ idiom — RAII.
By Blog Staff | May 27, 2014 08:37 AM | Tags: None
Did you know that C++ is a hot language for mobile development? This seems to be widely known among C++ developers, but surprisingly widely unknown in the non-C++ programming community at large. Two of the major reasons why C++ is currently experiencing this surge in mobile interest are:
In that vein, here's a post from just before the U.S. long weekend about using C++ for cross-platform mobile development.
Expect to see more news like this. Also, expect to see talks on using C++ for modern cross-platform mobile development as one of the hot topics at CppCon this September.
How Dropbox Uses C++ for Cross-Platform iOS and Android Development
by Ole Begemann
From the article:
When work started on the Mailbox app for Android, the team made the choice to write a large portion of the non-UI code in C++ — rather than rewriting the entire app in Java — with the goal of sharing that common C++ layer between iOS and Android. The iOS app used Core Data at the time, so migrating it off of Core Data to the shared C++ library was also part of the process. C++ seemed like an obvious choice because it is available on every platform and team members preferred the language over Java.
The Carousel team made the same choice since launching simultaneously on iOS and Android was an important goal from the start.