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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...

Safe Clearing of Private Data

By Andrey Karpov | Apr 6, 2016 05:27 AM | Tags: vulnerability security memset basics

We often need to store private data in programs, for example passwords, secret keys, and their derivatives, and we usually need to clear their traces in the memory after using them so that a potential intruder can't gain access to these data. In this article we will discuss why you can't clear private data using memset() function.

Safe Clearing of Private Data

by Roman Fomichev

From the article:

So, both gcc and clang decided to optimize our code. Since the memory is freed after calling the memset() function, the compilers treat this call as irrelevant and delete it.

Using C++ Coroutines to simplify async UWP code--Eric Mittelette

By Marco Arena | Apr 5, 2016 05:28 AM | Tags: visual studio intermediate experimental

The async pattern needed to write UWP apps (or simply "Universal apps") is not so easy to grasp, especially in C++. Eric from the Visual C++ team explains how the experimental Coroutines feature available in Visual Studio 2015 helps simplify async UWP code:

Using C++ Coroutines to simplify async UWP code

From the article:

C++ Coroutines can simplify your async code, and make the code easy to understand, write, and maintain...

STL Algorithms in Action -- Haitham Gad

By Mantosh Kumar | Mar 27, 2016 11:32 PM | Tags: intermediate

Use of STL Algorithm as building block to implement various high level algorithms.

STL Algorithms in Action

by Haitham Gad

From the article:

We saw variations of three common sorting algorithms implemented generically and compactly using STL algorithms. In general, STL algorithms are more applicable than they look. The key to utilizing them is to always ask whether the raw loop I’m about to write (or the one I’m reading) can be replaced by a packaged STL algorithm. You’d be surprised how many times this question can be answered affirmatively.

Trip Report: C++ Standards Meeting in Jacksonville, February 2016--Botond Ballo

By Adrien Hamelin | Mar 25, 2016 04:33 AM | Tags: experimental community

ANother trip report:

Trip Report: C++ Standards Meeting in Jacksonville, February 2016

by Botond Ballo

From the article:

Last week I attended a meeting of the ISO C++ Standards Committee in Jacksonville, Florida. This was the first committee meeting in 2016; you can find my reports on the 2015 meetings here (May 2015, Lenexa) and here (October 2015, Kona). These reports, particularly the Kona one, provide useful context for this post...

Concepts without Concepts--Andrzej Krzemieński

By Adrien Hamelin | Mar 22, 2016 01:52 PM | Tags: c++11 advanced

Concetps are good, but how can we get them?

Concepts without Concepts

by Andrzej Krzemieński

From the article:

“Concept” can mean two things in the context of C++ generic libraries:

  1. Something informal: something we know about template parameters, and can tell to other human programmers, e.g. in documentation.
  2. A language feature.

This post is about concepts in the first sense. It claims that we had concepts for quite a while already, and shows how we can use them to make generic libraries easier to use...

Guidelines Support Library Review: string_span--Marius Bancila

By Adrien Hamelin | Mar 22, 2016 01:39 PM | Tags: c++14 basics

What is a string_span?

Guidelines Support Library Review: string_span<T>

by Marius Bancila

From the article:

In a previous post I have introduced the span<T> type from the Guidelines Support Library. This is a non-owning range of contiguous memory recommended to be used instead of pointers (and size counter) or standard containers (such as vector or array). span<T> can be used with strings, but the Guidelines Support Library provides a different span implementation for various types of strings. These string span types are available in the string_span.h header.