Quick Q: c++ lambda capture by value

By Adrien Hamelin | Jun 6, 2016 01:22 PM | Tags: None

Quick A: A capture by value is a copy.

Recently on SO:

c++ lambda capture by value

That's because the variable is captured by value (i.e. copied) only once, when you define the lambda. It's not "updated" as you may believe. The code is roughly equivalent to:

#include <iostream>

int x = 0;
struct Lambda
{
    int _internal_x; // this is used to "capture" x ONLY ONCE
    Lambda(): _internal_x(x) {} // we "capture" it at construction, no updates after
    void operator()() const
    {
        std::cout << _internal_x << std::endl;
    }
} qqq;

int main()
{
    qqq();
    x = 77; // this has no effect on the internal state of the lambda
    qqq();
}

C++ in Competitive Programming: string basics--Marco Arena

By Marco Arena | Jun 6, 2016 12:28 AM | Tags: basics

In this installment we’ll meet std::string and some standard functions:

C++ in Competitive Programming: string basics

by Marco Arena

From the article:

We need a type representing a sequence of characters and in C++ we have std::string, the main string datatype since 1998 (corresponding to the first version of the ISO C++ standard – known as C++98)...

C++ Annotated: March – May 2016--Anastasia Kazakova

By Adrien Hamelin | Jun 3, 2016 02:30 PM | Tags: community

An overview of the recent C++ world:

C++ Annotated: March – May 2016

by Anastasia Kazakova

From the article:

In this edition:

• Conferences
• News & Stories
• Webinars
• Releases

VoidParam Puzzle -- Alex Marmer

By Alex Marmer | Jun 3, 2016 12:28 AM | Tags: None

Alex Marmer has openend a puzzle.

VoidParam Puzzle 

From the article:

How to handle 'void' parameter passed in a macro. He provides a solution as well.

In case that you have other or better solutions, don't hesitate to use the comment option on this site.

Compile Time Constants Part 1: Why We Need Them--Arne Mertz

By Adrien Hamelin | Jun 1, 2016 02:47 PM | Tags: performance intermediate

The title says it all:

Compile Time Constants Part 1: Why We Need Them

by Arne Mertz

From the article:

Compile time constants are an important part of C++. They contribute to program correctness and allow the optimizer to do a better job. Today I will deal with what is possible in terms of compile time constants and compile time calculations in C++03.

Quick Q: If nullptr_t isn't a keyword, why are char16_t and char32_t?

By Adrien Hamelin | Jun 1, 2016 02:41 PM | Tags: c++11 advanced

Quick A: To allow overloading with the underlying types of uint_least16_t and uint_least32_t

Recently on SO:

If nullptr_t isn't a keyword, why are char16_t and char32_t?

The proposal itself explains why: to allow overloading with the underlying types of uint_least16_t and uint_least32_t. If they were typedefed this wouldn't be possible.

Define char16_t to be a distinct new type, that has the same size and representation as uint_least16_t. Likewise, define char32_t to be a distinct new type, that has the same size and representation as uint_least32_t.

[N1040 defined char16_t and char32_t as typedefs to uint_least16_t and uint_least32_t, which make overloading on these characters impossible.]

As for why they aren't in the std namespace, this is for compatibility with the original C proposal. C++ prohibits the C definitions from appearing in its own version of <cuchar>

[c.strings] / 3

The headers shall not define the types char16_t, char32_t, and wchar_t (2.11).

The types then would need to be global typedefs, which carries its own set of issues such as

typedef decltype(u'q') char16_t;

namespace foo {
  typedef int char16_t;
}

The reason for std::nullptr_t not being a keyword can be found in the question you linked

We do not expect to see much direct use of nullptr_t in real programs.

making nullptr_t the real exception here.

 

C++ for Games: Performance, Allocations and Data Locality -- Sergey Ignatchenko

By Blog Staff | May 31, 2016 11:39 AM | Tags: None

Well-illustrated, and well-illustrated, gems:

C++ for Games: Performance, Allocations and Data Locality

by Sergey Ignatchenko

From the draft chapter:

One further thing to keep in mind with regards to 90-10 (or 70-30) rule is that even if only performance of 10% of the code matters, the rest of the code can still affect performance of critical 10% in a Pretty Bad Way :-( ...

C++ Performance: Common Wisdoms and Common "Wisdoms" -- Sergey Ignatchenko

By Blog Staff | May 30, 2016 05:31 PM | Tags: None

Sergey is writing a book and making draft chapters available for review. Here are sSome tried-and-true, well-illustrated and entertaining tips:

C++ Performance: Common Wisdoms and Common "Wisdoms"

by Sergey Ignatchenko

From the draft chapter intro:

The opposite of a fact is falsehood, but the opposite of one profound truth may very well be another profound truth. — Niels Bohr

There are quite a few common wisdoms when it comes to C++ and games. As it always the case when facing a bunch of common wisdoms, some of them have their merits, some are obsolete-beyond-belief, and some are just taken from a very different context and are not really applicable. Let’s take a look at the most popular ones...

Quick Q: Is final used for optimization in C++?

By Adrien Hamelin | May 27, 2016 02:37 PM | Tags: performance intermediate

Quick A: Possibly.

Recently on SO:

Is final used for optimization in C++?

It can be.

An optimisation along these lines would relate to the "de-virtualization" of the virtual calls. This is not always immediately affected by the final of the class nor method. Albeit they offer help to determine this, the normal rules of the virtual functions and class hierarchy apply.

If the compiler can determine that at runtime a particular method will always be called (e.g. given the OP example, with an automatic object), it could apply such an optimisation anyway, irrespective of whether the method is final or not.

Optimisations fall under the as-if rule, that allow the compiler to apply any transformation so long as the observable behaviour is as-if the original code had been executed.

CppCon 2015 What's New in Visual C++ 2015 and Future Directions--Steve Carroll • Ayman Shoukry

By Adrien Hamelin | May 27, 2016 02:30 PM | Tags: community advanced

Have you registered for CppCon 2016 in September? Don’t delay – Early Bird registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

What's New in Visual C++ 2015 and Future Directions

by Steve Carroll • Ayman Shoukry

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

In this talk, we'll discuss new features, optimizations, and scenarios in Visual Studio 2015. We'll cover new backend optimizations, improved build throughput, new productivity and diagnostics features, and give a detailed update on our conformance progress, as well as talk about cool new c++1y features that we are shipping from await to modules.

Visual Studio isn't just for Microsoft platform developers. We'll also demonstrate our latest cross platform C++ development features for Android and iOS. We'll also give a sneak peak at our work on combining the Clang frontend with our existing backend to bring Clang support for Windows to Visual Studio.