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Fast Polymorphic Collections with Devirtualization -- Joaquín M López Muñoz

By Blog Staff | May 9, 2014 08:17 AM | Tags: intermediate

munoz.pngStill on the theme of "contiguous enables fast," a followup on the recent "Fast Polymorphic Collections" article:

Fast Polymorphic Collections with Devirtualization

by Joaquín M López Muñoz

From the article:

The poly_collection template class we implemented for fast handling of polymorphic objects can be potentially speeded up in the case where some of the derived classes it manages are known to the compiler at the point of template instantiation...

Allowing for the specification of a list of statically known derived class types as part of a poly_collection instantiation opens up possibilities for internal performance optimizations that do not impact the usage interface of this template class. The actual improvements achieved depend very much on the compiler being used, but in general are greater when passing polymorphic functors (such as generic lambdas) to for_each and qualifying virtual functions as final where possible.

Introducing emplacer -- Tim

By Blog Staff | May 9, 2014 06:44 AM | Tags: intermediate

Another nice way to have a polymorphic collection without sacrificing that performance-precious contiguous memory layout:

Introducing emplacer: allocate subtypes of an abstract base class directly in a container

by Tim

From the article:

So I complained to my friend Jeremy that C++ should be able to do this. This isn't Java, I shouldn't have to do a separate allocation for each object...

As alluded to earlier, you can also use it in containers. Here's an example:

std::vector<ShapeAny> shapes;

shapes.emplace(shapes.end())->emplace<Rect>(3, 4);
shapes.emplace(shapes.end())->emplace<Square>(3);

//emplace returns reference to *this, so you can use it like this too
shapes.push_back(ShapeAny().emplace<Rect>(5, 6));
shapes.push_back(ShapeAny().emplace<Circle>(1));

for (auto shape: shapes) {
  std::cout << shape->area() << std::endl;
}

Preface to Programming: Principles and Practice Using C++, 2nd Edition -- Bjarne Stroustrup

By Blog Staff | May 8, 2014 10:16 AM | Tags: basics

programming-2e.jpgStroustrup's introduction to programming book has now been updated for modern C++. The Preface was posted on InformIT:

Preface to Bjarne Stroustrup's Programming: Principles and Practice Using C++, 2nd Edition

by Bjarne Stroustrup

From the preface:

This book is for someone who has never programmed before but is willing to work hard to learn. It helps you understand the principles and acquire the practical skills of programming using the C++ programming language. My aim is for you to gain sufficient knowledge and experience to perform simple useful programming tasks using the best up-to-date techniques. How long will that take? As part of a first-year university course, you can work through this book in a semester...

Dangerous int-to-string conversions -- Andrzej Krzemieński

By Blog Staff | May 8, 2014 08:05 AM | Tags: None

Note that the article doesn't mention to_string, which is the preferred C++11 way to convert an int to a string. But it does point out an issue -- you can assign an int to a string, including by accident.

Dangerous int-to-string conversions

by Andrzej Krzemieński

From the article:

And now, because int is implicitly convertible to char, our unexpected conversion from int to std::string ‘works’ (under some definition of ‘work’)...

A tale of noexcept swap for user-defined classes in C++11 -- Sumant Tambe

By Blog Staff | May 8, 2014 06:17 AM | Tags: None

From the C++ Truths blog, with a creative use of std::tuple:

A tale of noexcept swap for user-defined classes in C++11

by Sumant Tambe

From the article:

I like my strong exception safety in my little copy-assignment operator so I don’t want my swap to throw but I don’t want my program to std::terminate() if an exception is really thrown. With all that in mind, I would rewrite the swap as follows...

This is not unlike what’s proposed by others but there’s more. The static assert looks awful and looks redundant. There is already a standard library utility that does the same thing: std::tuple. As mentioned before, std::tuple’s swap throws if any member swap throws. We use it here to make our job a lot easier...

C++ User Group Meetings in May

By Meeting C++ | May 7, 2014 03:11 AM | Tags: usergroup community basics

Again, a list of user group meetings for this month. In total its going to be 16 user groups meeting this month:

C++ User Group Meetings in May 2014

by Jens Weller

From the Article:

The Meetings

    8th May C++ UG Aachen - SIMD Programmierung
    8th May C++ UG Belgium
        Parallelism in the C++ Standard, what to expect from C++17
        Asynchronous Programming with futures and await
    8th May C++ UG Dresden - C++ Memory Model
    8th May C++ UG New York - Whats next for C++
    13th May C++ UG Philadelphia - Profiling and Perfomance
    14th May C++ UG San Francisco/Bay area
    15th May C++ UG Malmö/Sweden - Battle of the build systems
    19th May C++ UG Denver - CppNow, Eclipse Configuration, Qt Creator and more...
    20th May C++ UG Berlin - C++ in the demo scene
    21st May C++ UG Düsseldorf - Expression Templates
    21st May C++ UG Hamburg
    21st May C++ UG Seattle/Northwest - Agile Architecture
    23rd May C++ UG Paris
        Introspection et reflection en C++
        Le SIMD en pratique avec boost SIMD
        Clang & C++
    27th May C++ UG Chicago
    28th May C++ UG Heidelberg
    28th May C++ UG San Francisco/Bayarea - C++Now tripreport

Fast Polymorphic Collections -- Joaquín M López Muñoz

By Blog Staff | May 5, 2014 04:44 AM | Tags: performance intermediate efficiency

munuz-poly.PNGOn the theme of "contiguous enables fast":

Fast Polymorphic Collections

by Joaquín M López Muñoz

From the article:

poly_collection behaves excellently and is virtually not affected by the size of the container. For n < 105, the differences in performance between poly_collection and a std::vector of std::unique_ptrs are due to worse virtual call branch prediction in the latter case; when n > 105, massive cache misses are added to the first degrading factor.

A C error handling style that plays nice with C++ exceptions

By Stefanus Du Toit | May 4, 2014 07:52 AM | Tags: intermediate

If you've ever wondered why someone might throw an exception from a destructor, this article provides a legitimate example:

A C Error Handling Style that Plays Nice with C++ Exceptions

by Stefanus Du Toit

From the article:

By choosing a particular convention for a C API's error handling, we were able to very conveniently translate errors from the C API to C++ exceptions. ... Every experienced C++ programmer I know has opinions on how errors should be handled. I've found this style to be quite useful when layering C++ on top of C, and I think there's some beauty in the interplay between C and C++ here.