C++14 for Qt programmers -- Olivier Goffart

By Blog Staff | Nov 21, 2014 09:12 AM | Tags: None

For those who know how to pronounce Qt, note that this title is not intended as a beauty judgment:

C++14 for Qt programmers

by Olivier Goffart

From the article:

C++14 is the name of the version of the standard to be released this year. While C++11 has brought many more feature that took time to be implemented by the compilers, C++14 is a much lighter change that is already implemented by compilers such as clang or gcc.

Qt 5 already was adapted in many ways so you can make use of the new features of C++11. You can read about that in my previous article. C++11 in Qt5. This article mention some of the changes in C++14 and the impact on Qt users...

Quick Q: Is it idiomatic to make X objects immutable by making all X member data const? -- SO

By Blog Staff | Nov 21, 2014 04:31 AM | Tags: None

Quick A: Yes.

Recently on SO:

Idiomatic way to declare C++ immutable classes

So I have some pretty extensive functional code where the main data type is immutable structs/classes. The way I have been declaring immutability is "practically immutable" by making member variables and any methods const.

struct RockSolid {
   const float x;
   const float y;
   float MakeHarderConcrete() const { return x + y; }
}

Is this actually the way "we should do it" in C++? Or is there a better way?

Quick Q: Which is more efficient, push_back(move(var)) or emplace_back(var)? -- StackOverflow

By Blog Staff | Nov 20, 2014 04:25 AM | Tags: None

Quick A: 1. Those cases are not equivalent. 2. Emplace is more for when you don't already have a named object of the correct type...

Recently on SO:

Efficiency of C++11 push_back() with std::move versus emplace_back() for already constructed objects

In C++11 emplace_back() is generally preferred (in terms of efficiency) to push_back() as it allows in-place construction, but is this still the case when using push_back(std::move()) with an already-constructed object?

For instance, is emplace_back() still preferred in cases like the following?

std::string mystring("hello world");
std::vector<std::string> myvector;

myvector.emplace_back(mystring);
myvector.push_back(std::move(mystring));
// (of course assuming we don't care about using the value of mystring after)

Additionally, is there any benefit in the above example to instead doing:

myvector.emplace_back(std::move(mystring));

or is the move here entirely redundant, or has no effect?

Quick Q: How do I make an array of shared_ptrs to unrelated types? -- StackOverflow

By Blog Staff | Nov 19, 2014 04:17 AM | Tags: None

Quick A: Try vector<shared_ptr<boost::any>>.

Recently on SO:

Array of shared pointers to different classes

I am new to c++11 programming and now I'm trying to figure out if it is possible to create an array of shared pointers to different types. For example, something like that:

vector<shared_ptr<**???**>> v;
v.push_back(shared_ptr<int>(new int));
v.push_back(shared_ptr<MyClass>(new MyClass()));

or any other way to pass shared_ptr without knowing its type.

Functional Programming in C++ -- John Carmack

By Blog Staff | Nov 17, 2014 03:18 AM | Tags: None

In case you missed it:

Functional Programming in C++

by John Carmack

From the article:

... My pragmatic summary: A large fraction of the flaws in software development are due to programmers not fully understanding all the possible states their code may execute in. In a multithreaded environment, the lack of understanding and the resulting problems are greatly amplified, almost to the point of panic if you are paying attention. Programming in a functional style makes the state presented to your code explicit, which makes it much easier to reason about, and, in a completely pure system, makes thread race conditions impossible.

I do believe that there is real value in pursuing functional programming, but it would be irresponsible to exhort everyone to abandon their C++ compilers and start coding in Lisp, Haskell, or, to be blunt, any other fringe language...

Quick Q: What type do lambdas get compiled into? -- StackOverflow

By Blog Staff | Nov 14, 2014 09:37 AM | Tags: basics

Quick A: A compiler-generated type that stores the captured variables in its data members, and exposes the function signature and body as its operator().

Recently on SO:

What type do lambdas get compiled into?

As I know all data types must be known at compile time, and lambda is not a type. Does lambda got translated into anonymous struct with operator() or std::function wrapped?

For example,

std::for_each(v.begin(), v.end(), [](int n&){n++;});

Tiny Metaprogramming Library -- Eric Niebler

By Blog Staff | Nov 13, 2014 08:37 PM | Tags: experimental advanced

We like to link to articles at all levels. This one's near the top of the scale, for those looking for a real challenge:

Tiny Metaprogramming Library

by Eric Niebler

As the intro says [emphasis ours]:

(Difficult-to-grok metaprogramming below. Not for the faint of heart.)

From the rest of the introduction:

At the recent Urbana-Champaign meeting of the C++ Standardization Committee, Bill Seymour presented his paper N4115: Searching for Types in Parameter Packs which, as its name suggests, describes a library facility for, uh, searching for a type in a parameter pack, among other things. It suggests a template called packer to hold a parameter pack:

// A class template that just holds a parameter pack:
template <class... T> struct packer { };

Many of you are probably already familiar with such a facility, but under a different name:

// A class template that is just a list of types:
template <class... T> struct typelist { };

It became clear in the discussion about N4115 that C++ needs a standard typelist template and some utilities for manipulating them. But what utilities, exactly? ...

Samples for using LLVM and Clang as a library -- Eli Bendersky

By Blog Staff | Nov 12, 2014 08:03 AM | Tags: None

Another fresh article on Clang:

Samples for using LLVM and Clang as a library

by Eli Bendersky

From the article:

My llvm-clang-samples repository has been public for over a year, and has become quite popular recently. I figured it's about time I write a quick blog post explaining how it came to be and what the principles behind it are.

What makes Clang so special? -- CoderGears

By Blog Staff | Nov 12, 2014 08:00 AM | Tags: None

Today on CoderGears:

What makes Clang so special?

by CoderGears Team

From the article:

It’s proven that Clang is a mature compiler for C and C++ as [are the] GCC and Microsoft compilers, but what makes it special is the fact that it’s not just a compiler. It’s also an infrastructure to build tools. Thanks to its library based architecture which makes the reuse and integration of functionality provided more flexible and easier to integrate into other projects...

Effective Modern C++ available today -- Scott Meyers

By Blog Staff | Nov 11, 2014 01:01 AM | Tags: None

Available today on O'Reilly and Amazon, in print in early December:

EMC++ Exits Publishing Purgatory!

by Scott Meyers

From the announcement:

I just received the following from O'Reilly: "Congratulations! Your book went to print on Friday, and we've now completed production. The Retail Availability Date for ebooks on oreilly.com and Amazon is tomorrow, 11/11. For print books, it's estimated at 12/2."