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N4590: PL22.16/WG21 draft agenda: 20-25 Jun 2016, Oulu, FI -- Clark Nelson

By Blog Staff | Apr 12, 2016 01:11 PM | Tags: None

A new WG21 paper is available. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4590

Date: 2016-04-07

PL22.16/WG21 draft agenda: 20-25 Jun 2016, Oulu, FI

by Clark Nelson

Excerpt:

Meeting objectives The primary goals of this meeting will be:

  • Approve a CD for C++17
  • Advance Library Fundamentals v2 toward TS
  • Advance Networking toward PDTS
  • Advance Parallelism v2 toward PDTS
  • Advance Ranges toward PDTS

Quick Q: Is Stephen Lavavej's Mallocator the same in C++11?

By Adrien Hamelin | Apr 12, 2016 11:41 AM | Tags: intermediate c++11

Quick A: No, it has changed.

Recently on SO:

Is Stephen Lavavej's Mallocator the same in C++11?

STL himself has an answer to this question in his STL Features and Implementation techniques talk at CppCon 2014 (Starting at 26'30).

The slides are on github.

I merged the content of slides 28 and 29 below:

#include <stdlib.h> // size_t, malloc, free
#include <new> // bad_alloc, bad_array_new_length
template <class T> struct Mallocator {
  typedef T value_type;
  Mallocator() noexcept { } // default ctor not required
  template <class U> Mallocator(const Mallocator<U>&) noexcept { }
  template <class U> bool operator==(
    const Mallocator<U>&) const noexcept { return true; }
  template <class U> bool operator!=(
    const Mallocator<U>&) const noexcept { return false; }

  T * allocate(const size_t n) const {
      if (n == 0) { return nullptr; }
      if (n > static_cast<size_t>(-1) / sizeof(T)) {
          throw std::bad_array_new_length();
      }
      void * const pv = malloc(n * sizeof(T));
      if (!pv) { throw std::bad_alloc(); }
      return static_cast<T *>(pv);
  }
  void deallocate(T * const p, size_t) const noexcept {
      free(p);
  }
};

Note that it handles correctly the possible overflow in allocate.

Course: Boost Your Productivity with Modern C++ -- Peter Gottschling

By Blog Staff | Apr 9, 2016 03:18 PM | Tags: None

peter-gottschling.jpgA repeat of last year's popular course, again being held in English and German:

Boost Your Productivity with Modern C++

by Peter Gottschling

Abstract:

Templates (generic programming)

  • Function templates
  • Class templates
  • Variadic Templates (C++11)
  • Concepts
  • Specialization
  • Template arguments that are not types
  • Functors
  • Lambda functions (C++11)

Standard Template Library

  • Iterator concept
  • Containers
  • Functions
  • Meta-programming
  • Let the compiler compute
  • Providing type informations
  • Auto and decltype (C++11)
  • Const-adaptive classes
  • Expression templates

Other advanced and new techniques

  • Calling functions from derived classes without overhead
  • RValues and move semantics (C++11)
  • Initialization lists (C++11)
  • New for-loops (C++11)

Peter Gottschling is author of the Matrix Template Library 4, co-author of the Boost Graph Library and other scientific libraries. He is vice-chair of DIN's programming language group and head of the German delegation in the ISO committee for C++ standardization. He is managing director of SimuNova and taught C++ at TU Dresden, TU Berlin and Indiana University.

Quick Q:Is it possible in C++ to iterate over a std::map with unpacked key and value?

By Adrien Hamelin | Apr 8, 2016 01:05 PM | Tags: intermediate experimental

Quick A: An easy solution is not supported by the standard, it may come later.

Recently on SO:

Is it possible in C++ to do std::map<> “for element : container” iteration with named variables (eg, key and value) instead of .first and .second?

You could write a class template:

template <class K, class T>
struct MapElem {
    K const& key;
    T& value;

    MapElem(std::pair<K const, T>& pair)
        : key(pair.first)
        , value(pair.second)
    { }
};

with the advantage of being able to write key and value but with the disadvantage of having to specify the types:

for ( MapElem<int, std::string> kv : my_map ){
    std::cout << kv.key << " --> " << kv.value;
}

And that won't work if my_map were const either. You'd have to do something like:

template <class K, class T>
struct MapElem {
    K const& key;
    T& value;

    MapElem(std::pair<K const, T>& pair)
        : key(pair.first)
        , value(pair.second)
    { }

    MapElem(const std::pair<K const, std::remove_const_t<T>>& pair)
        : key(pair.first)
        , value(pair.second)
    { }
};

for ( MapElem<int, const std::string> kv : my_map ){
    std::cout << kv.key << " --> " << kv.value;
}

It's a mess. Best thing for now is to just get used to writing .first and .second and hope that the structured bindings proposal passes, which would allow for what you really want:

for (auto&& [key, value] : my_map) {
    std::cout << key << " --> " << value;
}

Sessions and object lifetimes--Andrzej Krzemieński

By Adrien Hamelin | Apr 8, 2016 12:49 PM | Tags: c++11 advanced

How will you move?

Sessions and object lifetimes

by Andrzej Krzemieński

From the article:

In this post we will see how C++ object lifetime can be used to control the duration of sessions: time spent owing and using a resource. The goal is to get a better understanding of what tools the language offers for using and sharing resources efficiently...

CppCast Episode 52: Macchina.io with Günter Obiltschnig

By robwirving | Apr 8, 2016 06:34 AM | Tags: None

Episode 52 of CppCast the only podcast for C++ developers by C++ developers. In this episode Rob and Jason are joined by Günter Obiltschnig to discuss the macchina.io library for IoT C++ development.

CppCast Episode 52: Macchina.io with Günter Obiltschnig

by Rob Irving and Jason Turner

About the interviewee:

Günter is the founder of the POCO C++ Libraries and macchina.io open source projects. He has been programming computers since age 12. In his career he has programmed everything from 8-bit home computers (C64, MSX) to IBM big iron systems (COBOL and JCL, VM/CMS and CICS), various Unix systems, OpenVMS, Windows NT in its various incarnations, the Mac (classic Mac OS and OS X), to embedded devices and iPhone/iPad. He has a diploma (MSc. equivalent) in Computer Science from the University of Linz, Austria.

His current main interests are embedded systems, cross-platform C++ development, JavaScript and, foremost, the Internet of Things. When not working, he spends time with his family or enjoys one of his hobbies — sailing, running, swimming, skiing, listening to or making music, and reading.

CppCon opens Call for Submissions

By Jon Kalb | Apr 7, 2016 03:30 AM | Tags: community

CppCon has announced its call for submission for 2016. 

CppCon: The C++ Conference

Call for Submission

From the announcement:

The deadline for submissions is May 22nd and the conference face gathering for the entire C++ community. The conference is organized by the C++ community for the community and so we invite you to present.