Quick Q: Are the experimental features of modern C++ reliable for long-term projects?

By Adrien Hamelin | Apr 14, 2017 01:03 AM | Tags: community basics

Quick A: No

Recently on SO:

Are the experimental features of modern C++ reliable for long-term projects?

Is it guaranteed that all compliant compilers have the same experimental features?

No, experimental features are optional.

Are experimental features prone to big changes that make them unreliable?

Yes, the C++ committee might even decide to abandon a feature or in the process of standardization a defect might come up that would force a feature to change.

Generally, it's not a good idea to depend on experimental features. Experimental features are exactly what the word says (i.e., to experiment with).

Post-Conditions on Self-Move--Eric Niebler

By Adrien Hamelin | Apr 5, 2017 02:24 PM | Tags: c++11 advanced

An issue we do not think often about:

Post-Conditions on Self-Move

by Eric Niebler

From the article:

TL;DR: In addition to the usual rule about move operations leaving the source object in a valid but unspecified state, we can add an additional guideline (not quite a rule, but follow it anyway):

Self-move assignment should “work” and leave the object in a valid but unspecified state.

Quick Q: Prevent user from derive from incorrect CRTP base

By Adrien Hamelin | Apr 5, 2017 02:15 PM | Tags: intermediate

Quick A: Make it impossible to construct a class of the wrong type.

Recently on SO:

Prevent user from derive from incorrect CRTP base

1) make all constructors of Base private (if there are no constructors, add one)

2) declare Derived template parameter as friend of Base

template <class Derived>
class Base
{
private:

  Base(){}; // prevent undesirable inheritance making ctor private
  friend  Derived; // allow inheritance for Derived

public :

  void call ()
  {
      static_cast<Derived *>(this)->call_impl();
  }
};

After this it would be impossible to create any instances of the wrong inherited D2.

Quick Q: Conditionally acquire an std::mutex

By Adrien Hamelin | Apr 3, 2017 01:42 PM | Tags: intermediate c++11

Quick A: use a std::unique_lock with std::try_to_lock parameter in the constructor.

Recently on SO:

Conditionally acquire an std::mutex

It is actually unsafe to have a unique_lock accessible from multiple threads at the same time. I'm not familiar with the opencv portion of your question, so this answer is focused on the mutex/lock usage.

static std::mutex s_FAST_GPU_mutex;
{
   // Create a unique lock, attempting to acquire
   std::unique_lock<std::mutex> guard(s_FAST_GPU_mutex, std::try_to_lock);
   if (guard.owns_lock())
   {
       cv::gpu::FAST_GPU(/*params*/)(/*parameters*/);
       guard.unlock(); // Or just let it go out of scope later
   }
   else
   {
       cv::FAST(/*parameters*/);
   }
}

This attempts to acquire the lock, if it succeeds, uses FAST_GPU, and then releases the lock. If the lock was already acquired, then goes down the second branch, invoking FAST

Smelly std::pair and std::tuple--Arne Mertz

By Adrien Hamelin | Apr 3, 2017 01:36 PM | Tags: intermediate c++11

Do you use them badly?

Smelly std::pair and std::tuple

by Arne Mertz

From the article:

Depending on their use, std::pair and std::tuple can be code smells. That’s why we should be careful around these two.

Having a code smell is not a no-go, it’s more like a red flag. It’s one of those things that are not a problem themselves but rather a hint that there might be a less obvious problem hidden in the code.

Making things do stuff – Part 1--Glennan Carnie

By Adrien Hamelin | Apr 3, 2017 01:29 PM | Tags: community advanced

C++ for embedded too!

Making things do stuff – Part 1

by Glennan Carnie

From the article:

C has long been the language of choice for smaller, microcontroller-based embedded systems; particularly for close-to-the-metal hardware manipulation.

C++ was originally conceived with a bias towards systems programming; performance and efficiency being key design highlights.  Traditionally, many of the advancements in compiler technology, optimisation, etc., had centred around generating code for PC-like platforms (Linux, Windows, etc).  In the last few years C++ compiler support for microcontroller targets has advanced dramatically, to the point where Modern C++ is a increasingly attractive language for embedded systems development...

C++ User Group Meetings in April

By Meeting C++ | Apr 3, 2017 06:09 AM | Tags: community

The monthly overview of upcoming C++ User Group Meetings

C++ User Group Meetings in April 2017

by Jens Weller

From the article:

So far there are already 36 Meetings announced! There are 2 new C++ User Groups: Minneapolis, Stockholm (LLVM).

Variadic CRTP -- Steve Dewhurst

By Jon Kalb | Mar 29, 2017 10:40 AM | Tags: variadic templates crtp advanced

Steve Dewhurst has published a new paper under his category Once Weakly:

Variadic CRTP

by Steve Dewhurst

From article:

One problem with [the] traditional application of CRTP is that it’s inflexible....  We can get [more] flexibility by specifying the CRTP capability as a template template parameter.

Trip report: Winter ISO C++ standards meeting (Kona) -- Botond Ballo

By Blog Staff | Mar 27, 2017 07:17 PM | Tags: None

A new trip report from the just-concluded ISO C++ meeting:

Trip report: C++ standards meeting in Kona, February 2017

by Botond Ballo

From the article:

Conclusion

C++17 is effectively out the door, with its Draft International Standard sent out for ballot, and the official release expected later this year.

Development on C++20 is well under way, with numerous core language and library features already earmarked for it, and several Technical Specifications expected to be merged into it. A proposal for an overall vision for the release aims to focus the committee’s efforts on four headliner features – Concepts, Modules, Ranges, and Networking. That is, of course, not a guarantee these features will be in C++20 (nor is it intended to exclude other features!), but I believe with some luck and continued hard work we can make part of all of that plan a reality.

Modules, in particular, are expected to be a game-changer for C++...

Trip report: Winter ISO C++ standards meeting (Kona) -- Herb Sutter

By Blog Staff | Mar 24, 2017 05:03 PM | Tags: None

A trip report from the just-concluded ISO C++ meeting:

Trip report: Winter ISO C++ standards meeting (Kona), C++17 is complete

by Herb Sutter

From the article:

C++17 is done!

The big news is that we completed C++17, which dominated the work of the meeting: C++17 is now technically finished and being sent out for its final ISO balloting. All that remains for C++17 now is some ISO red tape and minor touch-up to get it officially published, which is expected to be just mechanical...