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Sneak Preview of C++17 -- Gabriel Ha

By kevstev | Dec 2, 2014 03:41 PM | Tags: None

A preview what is going into C++17 after the recent Standards Committee meeting. 

GoingNative 32: Sneak Preview of C++17

By Gabriel Ha

From the article: 

Join us with ISO Committee member (and Microsoft as well, of course =P) Gabriel Dos Reis, who graciously took the time to give us the inside scoop of some things that made it into C++17, as well as things that got taken out. All this is fresh off the press of the most recent C++ Standards Meeting...

 

 

C++ Has Become More Pythonic -- Jeff Preshing

By Daniel França | Dec 2, 2014 09:39 AM | Tags: python c++14 c++11

A nice article pointing out similarities between modern C++ and Python:

C++ Has Become More Pythonic

by Jeff Preshing

From the article:

C++ has changed a lot in recent years. The last two revisions, C++11 and C++14, introduce so many new features that, in the words of Bjarne Stroustrup, “It feels like a new language.”

It’s true. Modern C++ lends itself to a whole new style of programming – and you can’t help but feel Python’s influence on this new style. Ranged-based for loops, type deduction, vector and map initializers, lambda expressions. The more you explore modern C++, the more you find Python’s fingerprints all over it.

Was Python a direct influence on modern C++? Or did Python simply adopt a few common idioms before C++ got around to it? You be the judge...

Efficiency with Algorithms, Performance with Data Structures -- Chandler Carruth

By George Ryan | Dec 2, 2014 08:38 AM | Tags: performance c++14 c++11

carruth-cppcon2014.PNGAt the recent CppCon 2014, Chandler Carruth gave a great talk on using Modern C++ for writing high-performance applications. 

Efficiency with Algorithms, Performance with Data Structures

by Chandler Carruth

From the video introduction:

C++ programmers throughout the industry have an insatiable desire for writing high performance code. Unfortunately, even with C++, this can be really challenging. Over the past twenty years processors, memory, software libraries, and even compilers have radically changed what makes C++ code fast. Even measuring the performance of your code can be a daunting task. This talk will dig into how modern processors work, what makes them fast, and how to exploit them effectively with modern C++ code.

Quick Q: How do I add elements to a 2D vector of ints?--StackOverflow

By Jared Mulconry | Dec 2, 2014 03:56 AM | Tags: basics

Quick A: Index into the desired sub-vector and call push_back.

Recently on SO:

Inserting elements into 2D vector

So I'm creating a class that implements an adjacency list. Currently in my class definition I initialized two vectors:

vector<vector<int>> adjList;
vector<int> neighbors;

and I declared two functions that I plan to use to make it:

bool constructAdjList();
bool insertIntoAdjList(int, int);

It's getting difficult wrapping my head around 2D vectors. I understand that it is essentially a vector of vectors, but I'm confused about how to insert a new value into one of the "subvectors". For example, I am able to create an adjacency list in createAdjList that is empty with the following loop:

for (int i = 0; i < numOfValues; i++){
    neighbors.push_back(0);
    adjList.push_back(neighbors);
    neighbors.clear();
}

But how can I say, push_back the value 5 to the 4th vector in adjList, which would be represented in my insertIntoAdjList function as

insertIntoAdjList(4, 5);

I know I can access a specific value in a 2D vector by saying adjList[4][1], but how can I push one onto it?

Thanks!

A quick poll about order of evaluation -- Herb Sutter

By Blog Staff | Dec 1, 2014 01:48 PM | Tags: None

A quick Monday poll:

A quick poll about order of evaluation...

by Herb Sutter

From the article:

Consider this program fragment:

std::vector<int> v = { 0, 0 };
int i = 0;
v[i++] = i++;
std::cout << v[0] << v[1] << endl;

My question is not what it might print under today’s C++ rules. The third line runs afoul of two different categories of undefined and unspecified behavior.

Rather, my question is what you would like the result to be. Please let me know... [click for poll]

New optimizations for X86 in upcoming GCC 5.0 -- Evgeny Stupachenko

By Razvan Pascalau | Dec 1, 2014 07:11 AM | Tags: performance gcc efficiency compiler advanced

Fresh on the Intel Developer Zone blog:

New optimizations for X86 in upcoming GCC 5.0

by Evgeny Stupachenko

From the article:

Part 1. Vectorization of loads/stores group.

GCC 5.0 significantly improves vector code quality for load groups and store groups. By loads/stores group I mean iterated consecutive sequence of loads/stores. For example:

x = a[i], y = a[i + 1], z = a[i + 2] iterated by “i” is loads group of size 3

...

The most frequent case where loads/stores groups are applicable is array of structures.
  1. Image conversion (RGB structure to some other) ...
  2. N-dimentional coordinates. (Normalize array of XYZ points) ...
  3. Multiplication of vectors by constant matrix: ...

... GCC 5.0:

  1. Introduces vectorization of load/store groups of size 3
  2. Improves load groups vectorization for all supported sizes
  3. Maximizes load/store groups performance by generating code that is more optimal for particular x86 CPU...

 

Facebook Flint: Public domain C++ lint

By Felix Petriconi | Dec 1, 2014 02:02 AM | Tags: intermediate

Some months ago Facebook brought their C/C++ Facebook-Lint (Flint) analyzer into public domain and made it available on github.com/facebook/flint. Flint provides a lint framework and a number of C++11/14 style rules that we have found useful in our company.

This static code analyzer is not based on a C++ parser, but works with a tokenizer, completely written in D. (The previous C++ version of the program is still part of the repository.) 

Andrei Alexandescu gives detailed information in his blog entry:

Under the Hood: Building and open-sourcing flint

by Andrei Alexandrescu

... Writing a C++ linter in particular is not for the faint of heart because of C++'s high barrier to entry for parsing. That said, there are now dozens of C++ lint programs with a variety of features, some open sourced. So the natural question is why we chose to write our own instead of using a pre-existing one.

When we started this project, the lint programs we tried were too slow and most didn't support the C++11 features that our codebase had already started to use. Clang, which today would be logical starting point for a C++ analysis tool, offered too little support back then...

The distributed makefile is designed to work on Mac OS and Linux. But it is pretty easy to build a working flint.exe for Windows with Visual Studio and an installed D compiler and the corresponding plugin.

We prefer in our company either pairing or code reviews to ensure a high code quality. But we decided to use Flint as an additional safety-net and since the speed of the analyzer is so amazingly high, we were able to integrate it into the pre-commit hook of our Mercurial repository without any noticable performance drawbacks. So all to be committed C++ files are checked against a subset of all rules, that Flint supports.

(We disabled some Flint rules in the source code, because of missing C++11 capabilities of Visual Studio 2012/2013 and certain checks that does not make sence in our context.)

Consider automatically applying a lint tool in your project build. Whether you pick this or another one, it's worth checking out.

Quick Q: Are "++a" and "a = a.load() + 1" equivalent if 'a' is "atomic<int>"?--StackOverflow

By Jared Mulconry | Dec 1, 2014 01:57 AM | Tags: intermediate c++11

Quick A: No. Between a.load() and the addition and store to a is a window in which other threads can change the value of a, causing updates to be lost.

Recently on SO:

c++ atomic read/write misunderstanding

Why program with this code sometimes prints "2"?

int main() {
    std::atomic<int> a;
    a = 0;

    std::thread t1([&]{++a;});
    std::thread t2([&]{a++;});
    std::thread t3([&]{
        a = a.load() + 1;
    });

    t1.join();
    t2.join();
    t3.join();

    if (a != 3) {
        std::cout << "a: " << a << std::endl;
    }
}

I've thought std::atomic guarantees that all operations will be done atomically so writing here(incrementing) will use a memory barrier and we will have always "3" at the end of threads work. I've explored the code and found out that the problem thread is t3 but I can't understand why it is wrong.

C++ User Group Meetings in December

By Meeting C++ | Nov 30, 2014 08:39 AM | Tags: user group community

Its again the time to list the monthly meetings, this time its for December:

C++ User Group Meetings in December

by Jens Weller

From the Article

Three years ago, my own user group had its first meeting in December, being the second active C++ user group in Europe back in 2011. Since then a lot has changed, this December there are a lot more user groups meeting, and also we'll have the last premier C++ Event of the year: Meeting C++ is next week!

Meetings in December

    1.12 C++ UG Hungary - Template Metaprogramming With Better Tools
    2.12 C++ UG Chicago - The Bash Bug And The OpenSSL Bug
    3.12 C++ UG Saint Louis - Next meeting
    3.12 C++ UG Austin - Double Feature
    4.12 C++ UG Dublin - std::begin
    9.12 C++ UG San Francisco/ Bay area - C++11's New Pointer Types
    10.12 C++ UG Utah - Iterators\, Containers and Algorithms in the Standard Library
    10.12 C++ UG San Francisco/ Bay area - Presentation and Q&A
    11.12 C++ UG Dresden - Dezember Treffen
    13.12 C++ UG Pune, India - Introduction to C++ Template Metaprogramming and Domain Specific
    15.12 C++ UG Denver - Denver Tech Center C++ Developers
    15.12 C++ UG Austin - North Austin Monthly C/C++ Pub Social
    17.12 C++ UG Düsseldorf - Christmas special!
    18.12 C++ UG Paris - C++ FRUG #5 - L'asynchronisme en deux talks
    18.12 C++ UG Amsterdam - Let's have a meetup in December
    18.12 C++ UG Hamburg - Qt DevDays & Meeting C++