Home » Blog » Categories » Articles & Books

Articles & Books

Quick Q: int a[] = {1,2,}; Weird comma allowed. Any particular reason?

By Adrien Hamelin | Apr 20, 2018 12:29 PM | Tags: advanced

Quick A: For convenience.

Recently on SO:

int a[] = {1,2,}; Weird comma allowed. Any particular reason?

It makes it easier to generate source code, and also to write code which can be easily extended at a later date. Consider what's required to add an extra entry to:

int a[] = {
   1,
   2,
   3
};

... you have to add the comma to the existing line and add a new line. Compare that with the case where the three already has a comma after it, where you just have to add a line. Likewise if you want to remove a line you can do so without worrying about whether it's the last line or not, and you can reorder lines without fiddling about with commas. Basically it means there's a uniformity in how you treat the lines.

Now think about generating code. Something like (pseudo-code):

output("int a[] = {");
for (int i = 0; i < items.length; i++) {
    output("%s, ", items[i]);
}
output("};");

No need to worry about whether the current item you're writing out is the first or the last. Much simpler.

optional in Containers Ⅱ — Not All std::vector Usages Are The Same--Jonathan Müller

By Adrien Hamelin | Apr 20, 2018 12:27 PM | Tags: intermediate c++17

What do you think?

optional<T> in Containers Ⅱ — Not All std::vector Usages Are The Same

by Jonathan Müller

From the article:

Okay, so in the previous post I talked about putting optional<T> in container. I came to conclusions which I though were reasonable at the time, however, people — rightfully — pointed out some flaws in my argumentation...

compile-time iteration with C++20 lambdas -- Vittorio Romeo

By Vittorio Romeo | Apr 18, 2018 12:18 PM | Tags: c++17

This article covers various compile-time "iteration" constructs that rely on the upcoming "familiar template syntax for lambdas" C++20 feature.

compile-time iteration with C++20 lambdas

by Vittorio Romeo

From the article:

In this article I'm going to show you how to implement the above constructs, relying on a new nifty addition to C++20 lambdas: [P0428: "Familiar template syntax for generic lambdas"], by Louis Dionne. [...]

It shows how to implement constructs for the following operations:

Iterating over a list of types;
Iterating over a list of compile-time values;
Iterating over a compile-time integral range;
Enumerating a list of types alongside their indices.
The code provided works on g++ 8

How to Pass a Polymorphic Object to an STL Algorithm--Jonathan Boccara

By Adrien Hamelin | Apr 17, 2018 12:36 PM | Tags: stl intermediate

Did you ever try?

How to Pass a Polymorphic Object to an STL Algorithm

by Jonathan Boccara

From the article:

As we can read in the opening chapter of Effective C++, C++ is a federation of 4 languages:

  • the procedural part coming from C,
  • the object-oriented part,
  • the STL part (following a functional programming paradigm),
  • the generic part with templates.

And what’s more, all of those 4 sub-languages are part of one whole: the C++ language. Those 4 paradigms begin united in one language gives opportunities for them to interact – and often, those interactions create interesting situations.

Today we’re focusing on one particular interaction, between the object-oriented model and the STL. There could be multiple forms for this interaction, and the case we will look at is how to pass a polymorphic (that is, having virtual methods) function object to an STL algorithm.

uninitialized_tag in C++--Marius Elvert

By Adrien Hamelin | Apr 17, 2018 12:17 PM | Tags: performance advanced

Optimise or not?

uninitialized_tag in C++

by Marius Elvert

From the article:

No doubt, C++ is one of those languages you can use to squeeze out every last drop of your CPU’s processing power. On the other hand, it also allows a high amount of abstraction. However, micro-optimization seldom works well with nice abstractions...

C++17: The two line visitor explained--Marius Elvert

By Adrien Hamelin | Apr 16, 2018 01:00 PM | Tags: c++17 advanced

The power of C++17.

C++17: The two line visitor explained

by Marius Elvert

From the article:

If you have ever used an “idiomatic” C++ variant datatype like Boost.Variant or the new C++17 std::variant, you probably wished you could assemble a visitor to dispatch on the type by assembling a couple of lambda expressions like this:

auto my_visitor = visitor{
  [&](int value) { /* ... */ },
  [&](std::string const& value) { /* ... */ },
};

Quick Q: With “-fno-exceptions”, what happens with “new T”?

By Adrien Hamelin | Apr 16, 2018 12:46 PM | Tags: advanced

Quick A: The behaviour will likely stay the same.

Recently on SO:

With “-fno-exceptions”, what happens with “new T”?

The way I understand it, operator new is defined by libstdc++. If you now compile your own code with -fno-exceptions, you cannot catch any exceptions, but you will still be linking against the normal version of libstdc++, which does throw an exception.

So yes, new T will throw an exception, even with -fno-exception.

However, if you compiled libstdc++ with -fno-exception as well, things become different. Now, new T cannot throw an exception but, if I read the libstdc++ manual right it will call abort() instead.

It seems that, if you want your new T to return NULL on failure, the only way is to explicitely specify nothrow...