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By Marco Arena | Jun 5, 2019 06:43 AM | Tags: c++20 c++17 advanced
A new interpretation of a classical problem:
Kadane in next-gen C++
by Marco Arena
From the article:
We, programmers, get better results while thinking in patterns. We decompose complex problems in combinations of simpler patterns. However, many problems cannot be solved with known patterns. Here is where creativity kicks in...
By Adrien Hamelin | Jun 4, 2019 11:04 AM | Tags: intermediate c++14
Quick A: mostly for exception safety.
Recently on SO:
Differences between std::make_unique and std::unique_ptr with new
The motivation behind make_unique is primarily two-fold:
make_unique is safe for creating temporaries, whereas with explicit use of new you have to remember the rule about not using unnamed temporaries.
foo(make_unique<T>(), make_unique<U>()); // exception safe foo(unique_ptr<T>(new T()), unique_ptr<U>(new U())); // unsafe*The addition of make_unique finally means we can tell people to 'never' use new rather than the previous rule to "'never' use new except when you make a unique_ptr".
There's also a third reason:
make_unique does not require redundant type usage. unique_ptr<T>(new T()) -> make_unique<T>()None of the reasons involve improving runtime efficiency the way using make_shared does (due to avoiding a second allocation, at the cost of potentially higher peak memory usage).
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).
By Adrien Hamelin | Jun 3, 2019 11:55 AM | Tags: performance
Quick A: performance.
Recently on SO:
Why does moving std::optional not reset state?
In a word: Performance.
One of the chief motivating reasons for move semantics to exist in the first place is performance. So the special operations move construction and move assignment should be as fast as possible for all types...
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?
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...
By Adrien Hamelin | May 30, 2019 12:59 PM | Tags: community
The series continue.
C++ Core Guidelines: std::array and std::vector are your Friends
by Rainer Grimm
From the article:
In 99 % of your use-cases for a sequential container, you are totally fine with a std::array or a std::vector. What? If you don't believe me, read this post...
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...
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 } };
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...