Home » Blog » Categories »

The Cost of Dynamic (Virtual Calls) vs. Static (CRTP) Dispatch in C++ -- Eli Bendersky

By Blog Staff | Dec 9, 2013 12:14 PM | Tags: intermediate

eli-bendersky.PNGA nice dive into performance costs on at least one compiler, and on the difficulties of doing meaningful performance measurements on modern hardware. Be sure to read the short comment thread too.

The Cost of Dynamic (Virtual Calls) vs. Static (CRTP) Dispatch in C++

by Eli Bendersky

From the article:

A couple of years ago I wrote an article about the Curiously Recurring Template Pattern in C++, focusing on the motivation behind it and how to implement it.

That article mentioned runtime performance as the main reason for employing CRTP instead of the more traditional runtime polymorphism (dispatch via virtual functions). While some rationale for the cost of virtual calls was given, I didn’t go too deep into it. Today I want to fix that by carefully analyzing the performance of virtual calls as opposed to the static calls made possible by CRTP.

Mandatory precaution about benchmarks

Benchmarking in 2013 is really hard. ...

Using STL Vectors, and Efficient Vectors of Vectors -- Thomas Young

By Blog Staff | Dec 6, 2013 12:36 PM | Tags: intermediate basics

thomas-young.jpegThese are also the first two articles in a new blog by the creator of the PathEngine SDK.

Note: One or two of the points can be controversial, but the content is interesting and informative especially as an experience report.

Using STL Vectors

Efficient Vectors of Vectors

by Thomas Young

From the articles:

The stuff we do with vectors can be broadly categorised into two main use cases:

  • the construction of (potentially complex) preprocess objects, and
  • run-time buffers for queries, where buffer size requirements are fundamentally dynamic in nature

Preprocess objects include things like the pathfinding visibility graph. These objects can take time to build, but this is something that can be done by the game content pipeline, with preprocess data saved and loaded back from persistence by the game runtime.

The Curious Case of the Recurring Template Pattern -- K-Ballo

By Blog Staff | Dec 6, 2013 10:37 AM | Tags: intermediate

Do you remember CRTP? No? Then definitely read about it here:

The Curious Case of the Recurring Template Pattern

by K-ballo

Inheritance is a handy tool to simplify design and avoi code duplication. However, good old fashioned inheritance is not always the right tool for the job. What if a base class could know, at compile time, who derives from it? Enter the curiously recurring template pattern (CRTP)...

Quick Q: A lambda's return type can be deduced, so why can't a function's? -- StackOverflow

By Blog Staff | Dec 6, 2013 09:20 AM | Tags: intermediate

Quick A: It can, in C++14. In fact, this C++14 feature supported today in current versions of GCC and Clang with -std-c++1y and in the Visual C++ November 2013 CTP.

On SO:

A lambda's return type can be deduced by the return value, so why can't a function's?

#include <iostream>

int main(){

    auto lambda = [] {
        return 7;
    };

    std::cout << lambda() << '\n';

}

This program compiles and prints 7.
The return type of the lambda is deduced to the integer type based on the return value of 7.

Why isn't this possible with ordinary functions?

#include <iostream>

auto function(){
    return 42;
}

int main(){

    std::cout << function() << '\n';
}

error: ‘function’ function uses ‘auto’ type specifier without trailing return type

C++ User Group Meetings in December

By Meeting C++ | Dec 5, 2013 04:26 PM | Tags: community

Well, December brings a few more meetings of C++ User Groups this year:

C++ User Group Meetings in December

From the article:

This December feels a bit special, as my own user group was founded 2 years ago. We'll celebrate with cake and a C++ quiz! Also, a few other C++ User Groups do meet:

    11.12 C++ User Group San Francisco/Bay Area
    12.12 C++ User Group San Antonio -- 2 talks
    12.12 C++ User Group London
    12.12 C++ User Group Dresden -- virtual inheritance & CRTP
    17.12 C++ User Group Berlin -- the C++11 Memory Model
    18.12 C++ User Group Düsseldorf -- 2 years! We'll have cake and a C++ quiz!

C++Now 2014: 3 Days to Submissions Deadline

By Boris Kolpackov | Dec 5, 2013 04:25 PM | Tags: None

Only 3 days left before the submissions deadline for C++Now 2014!

C++Now is a general C++ conference for C++ experts and enthusiasts. It is not specific to any library/framework or compiler vendor and has three tracks with presentations ranging from hands-on, practical tutorials to advanced C++ design and development techniques. For more information about C++Now, see the conference's website.

Have you learned something interesting about C++ (e.g., a new technique possible in C++11)? Or maybe you have implemented something cool related to C++ (e.g., a C++ library)? If so, consider sharing it with other C++ enthusiasts by giving a talk at C++Now 2014. For more information on possible topics, formats, etc., see the call for submissions.

Say hello to wxWidgets3.0

By Meeting C++ | Dec 4, 2013 10:53 AM | Tags: wxwidgets intermediate c++11 basics

A few weeks ago wxWidgets3.0 was released, now it's time to take a look at it:

Say hello to wxWidgets3.0

From the Article

I remember the times, when wxWidgets 3.0 was already talked about, several years ago. Now, its been published in November, though I have to take a look at it. I've been using wxWidgets for years, but moved on to Qt for my own projects. So, lets have a look at wxWidgets 3.0...

Quick Q: Why have move semantics? -- StackOverflow

By Blog Staff | Dec 3, 2013 04:42 AM | Tags: basics

Quick A: Because value semantics are clean and naturally (exception-)safe, and avoid the brittleness of pre-C++11 workarounds that resort to owning raw pointers.

As often happens, the question contains the answer...

Why have move semantics?

... Can't the client already take advantage of pointers to do everything move semantics gives us? If so, then what is the purpose of move semantics?

Move semantics:

std::string f()
{
    std::string s("some long string");
    return s;
}
int main()
{
    // super-fast pointer swap!
    std::string a = f();
    return 0;
}

Pointers:

std::string *f()
{
    std::string *s = new std::string("some long string");
    return s;
}

int main()
{
    // still super-fast pointer swap!
    std::string *a = f();
    delete a;
    return 0;
}