Using variadic macros -- Andrzej Krzemieński

By Blog Staff | Jun 19, 2014 02:45 AM | Tags: None

The latest from the desk of Andrzej:

Using variadic macros

by Andrzej Krzemieński

From the article:

But what struck me was something different. Why is it only some compilers that rejected my code. Why did most of the other compilers accept my apparently buggy code and produced the right result?

The answer is in the title of this post. Boost.StaticAssert is clever and wherever possible it uses variadic macros. ... it is now OK: all these arguments along with the separating commas are forwarded further (e.g., to static_assert) to the code that knows how to interpret these tokens. This is a very nice usage of variadic macros.

Masking a Class in Boost Graph, Part 3: Finding the Path -- Vadim Androsov

By Blog Staff | Jun 16, 2014 07:19 AM | Tags: intermediate

Part 3 of Vadim's experience report about using Boost's graph support in an existing game app:

Masking a Class in Boost Graph. Part 3: Finding the Path

by Vadim Androsov

From the article:

In the previous articles of the series we’ve reviewed the adaptive process of the square game field for concepts of boost graphs. Now we’ll consider the process of finding the path in the square field. Implementation of boost search allows adapting the algorithm quite accurately. In this article we’ll provide just one example of such parameterization – an ability to create various lengths of graph edges. ...

Game Changer -- Tony DaSilva

By Blog Staff | Jun 16, 2014 06:25 AM | Tags: None

A little more fodder for those still trying to get their management or team to adopt modern C++:

Game Changer

by Tony DaSilva

From the article:

Even though I’m a huge fan of the man, I was quite skeptical when I heard Bjarne Stroustrup enunciate: "C++ feels like a new language". Of course, Bjarne was talking about the improvements brought into the language by the C++11 standard.

Well, after writing C++11 production code for almost 2 years now (17 straight sprints to be exact), I’m no longer skeptical. ... It seems that the authors of the “High Integrity C++” coding standard agree with my assessment. ...

Quick Q: Is unique_ptr guaranteed to store nullptr after move? -- StackOverflow

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_ptr guaranteed to store nullptr after move?

std::unique_ptr<int> p1{new int{23}};
std::unique_ptr<int> p2{std::move(p1)};
assert(!p1); // is this always true?

Generator functions in C++ -- Paolo Severini

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 resumable and await keywords 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. ...

Masking a Class in Boost.Graph -- Vadim Androsov

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. ...

Are lists evil? -- Bjarne Stroustrup

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:

• My 2012 "Going Native" Keynote.

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::list but 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 for std::lists and push_back()s is faster for vectors. 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::vector by 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.

Lightweight HTTP Server in less than 40 Lines on libevent and C++11 -- NYM

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.

Ref-qualifiers -- Andrzej Krzemieński

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....

Overload 121 is now available

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:

Overload 121

Stop the Constant Shouting

CONSTANTS often shout. Jonathan Wakely considers why this happens in C and what the alternatives are in C++.

Minimal Overhead for Multiple Interfaces

Using multiple interfaces can slow things down. Daniel Gutson and Pablo Oliva present an alternative.