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Quick Q: With arrays, why is it the case that a[5] == 5[a]?

By Adrien Hamelin | Jun 4, 2019 11:01 AM | Tags: intermediate

Quick A: See below

Recently on SO:

With arrays, why is it the case that a[5] == 5[a]?

The C standard defines the [] operator as follows:

a[b] == *(a + b)

Therefore a[5] will evaluate to:

*(a + 5)

and 5[a] will evaluate to:

*(5 + a)

a is a pointer to the first element of the array. a[5] is the value that's 5 elements further from a, which is the same as *(a + 5), and from elementary school math we know those are equal (addition is commutative).

The Difference Between std::copy_backward and std::copy with Reverse Iterators--Jonathan Boccara

By Adrien Hamelin | Jun 3, 2019 11:47 AM | Tags: stl intermediate

What do you think?

The Difference Between std::copy_backward and std::copy with Reverse Iterators

by Jonathan Boccara

From the article:

A couple of months ago, I made a talk at the ACCU conference about learning every algorithm there is in the STL. Amongst them, we covered std::copy_backward, that makes a copy of a source range to a destination range, starting from its end and working its way back to the beginning.

In the questions session at the end of the talk, attendant Oscar Forner rose an interesting point: is there any difference between performing a std::copy_backward versus performing a simple std::copy on the reverse iterators from the source collection?

strong_typedef - Create distinct types for distinct purposes--Anthony Williams

By Adrien Hamelin | May 30, 2019 01:39 PM | Tags: community

A common problem with a common solution made easier.

strong_typedef - Create distinct types for distinct purposes

by Anthony Williams

From the article:

One common problem in C++ code is the use of simple types for many things: a std::string might be a filename, a person's name, a SQL query string or a piece of JSON; an int could be a count, an index, an ID number, or even a file handle. In his 1999 book "Refactoring" (which has a second edition as of January 2019), Martin Fowler called this phenomenon "Primitive Obsession", and recommended that we use dedicated classes for each purpose rather than built-in or library types...

Heterogeneous Lookup in Ordered Containers, C++14 Feature--Bartlomiej Filipek

By Adrien Hamelin | May 29, 2019 12:26 PM | Tags: stl performance c++14

Did you know?

Heterogeneous Lookup in Ordered Containers, C++14 Feature

by Bartlomiej Filipek

From the article: 

If you have a map of strings, like std::map<std::string, int> m; and you want to find some element by m.find("abc"). Do you have to pay the price and construct a std::string object? Can you optimize it?

Let’s have a look at one feature enabled in C++14 that might help optimize such container access...

Quick Q: When should I make explicit use of the `this` pointer?

By Adrien Hamelin | May 29, 2019 12:20 PM | Tags: intermediate

Quick A: to disambiguate.

Recently on SO:

When should I make explicit use of the `this` pointer?

Usually, you do not have to, this-> is implied.

Sometimes, there is a name ambiguity, where it can be used to disambiguate class members and local variables. However, here is a completely different case where this-> is explicitly required.

Consider the following code:

template<class T>
struct A {
   int i;
};

template<class T>
struct B : A<T> {

    int foo() {
        return this->i;
    }

};

int main() {
    B<int> b;
    b.foo();
}

If you omit this->, the compiler does not know how to treat i, since it may or may not exist in all instantiations of A. In order to tell it that i is indeed a member of A<T>, for any T, the this-> prefix is required.

Note: it is possible to still omit this-> prefix by using:

template<class T>
struct B : A<T> {

    using A<T>::i; // explicitly refer to a variable in the base class

    int foo() {
        return i; // i is now known to exist
    }

};

Core C++ 2019 Trip Report--Anastasia Kazakova

By Adrien Hamelin | May 27, 2019 11:56 AM | Tags: community

It's trip report time!

Core C++ 2019 Trip Report

by Anastasia Kazakova

From the article:

More and more C++ events, community meetups, and conferences are appearing around the globe. 2019 is definitely looking like a year for new C++ conferences. Take, for example, C++ on Sea (UK, in February) or the upcoming CPPP (France, in June). Even C++ Russia now has two editions per year – one in Moscow and one in St. Petersburg. And, finally, there’s the event we just visited – Core C++, held in Tel Aviv, Israel...

C++ Core Guidelines: The Standard Library--Rainer Grimm

By Adrien Hamelin | May 20, 2019 01:10 PM | Tags: community

The guidelines explained further.

C++ Core Guidelines: The Standard Library

by Rainer Grimm

From the article:

Curiously, there is no section to the algorithms of the standard template library (STL) in this chapter. Curiously, because there is a proverb in the C++ community: If you write an explicit loop, you don't know the algorithms of the STL. Anyway. Only for completeness, let me start with the first three rules which provide not much beef...

Report from using std::cpp 2019

By Adrien Hamelin | May 13, 2019 12:06 PM | Tags: community

The statitistics.

Report from using std::cpp 2019

From the article:

On March, 7th, we had the sixth edition of using std::cpp (the C++ conference in Spain). The conference was again a on-day free event, and as every other year it was hosted at the Higher Polytechnic School of University Carlos III of Madrid in Leganés.

As many other years roughly 200 participants attended the conference. Most of the attendees were coming from industry...