The “unsigned” Conundrum—Tony “Bulldozer00” DaSilva

Are you clear with unsigned?

The “unsigned” Conundrum

by Tony “Bulldozer00” DaSilva

From the article:

A few weeks ago, CppCon16 conference organizer Jon Kalb gave a great little lightning talk titled “unsigned: A Guideline For Better Code“. Right up front, he asked the audience what they thought this code would print out to the standard console:

Even though -1 is obviously less 1, the program prints out “a is not less than b“. WTF?

DLib 19.2 released

Today a new version of DLib is available:

DLib 19.2 released

Release notes

by Davis King

From the article:

... So the obvious thing to do was to add an implementation of MMOD with the HOG feature extraction replaced with a convolutional neural network.  The new version of dlib, v19.2, contains just such a thing.  On this page you can see a short tutorial showing how to train a convolutional neural network using the MMOD loss function.  It uses dlib's new deep learning API to train the detector end-to-end on the very same 4 image dataset used in the HOG version of the example program.  Happily, and very much to the surprise of myself and my colleagues, it learns a working face detector from this tiny dataset.

Quick Q: Is the ‘override’ keyword just a check for a overriden virtual method?

Quick A: Yes.

Recently on SO:

Is the 'override' keyword just a check for a overriden virtual method?

That's indeed the idea. The point is that you are explicit about what you mean, so that an otherwise silent error can be diagnosed:

struct Base
    virtual int foo() const;

struct Derived : Base
    virtual int foo()   // whoops!
       // ...

The above code compiles, but is not what you may have meant (note the missing const). If you said instead, virtual int foo() override, then you would get a compiler error that your function is not in fact overriding anything.

Quick Q: Initializing a std::string with function return value, is there a copy?

Quick A: No, at worse it will be a move.

Recently on SO:

Initializing a std::string with function return value, is there a copy?

In general, if the std::string is constructed in the call and then returned most modern compilers with apply the return value optimization (a special case of copy elision). Your case in particular is the Named RVO (thanks @NathanOliver for pointing this out), if you want to look up the precise rules. From C++17 on this optimization is guaranteed through the standard.

Whether or not the optimization is applied is hard to tell, however if it is not, then in C++11 and above it is very likely that the std::string object in the scope of the function will be moved from and that the return value will be moved to. You could theoretically call std::move on the return value, but thereby you would also prevent any RVO from happening. While move may be efficient, RVO typically yields faster code, because nothing is moved or copied at all, but the object is constructed in place, so I would advise against doing it, and in favor of relying on your compiler.

How to avoid bugs using modern C++

One of the main problems with C++ is having a huge number of constructions whose behavior is undefined, or is just unexpected for a programmer. Let's see which techniques in modern C++ help writing not only simple and clear code, but make it safer and more reliable.

How to avoid bugs using modern C++

by Pavel Belikov

From the article:

Of course, there are some flaws in the range-based for: it doesn't allow flexible management of the loop, and if there is more complex work with indexes required, then for won't be of much help to us. But such situations should be examined separately. We have quite a simple situation: we have to move along the items in the reverse order. However, at this stage, there are already difficulties. There are no additional classes in the standard library for range-based for. Let's see how it could be implemented.

Great Expectations—Glennan Carnie

Let's review the basics!

Great Expectations

by Glennan Carnie

From the article:

Previously, we’ve looked at the basic concepts of function parameter passing, and we’ve looked at the mechanics of how parameters are passed at the Application Binary Interface (ABI) level.

Far too often we focus on the mechanisms and efficiency of parameter passing, with the goal: if it’s efficient then it’s good; that’s all there is to it.  In this article I want to move past simple mechanics and start to explore function parameter design intent – that is, what can I expect (to change) about the objects I use as function arguments; and what can I expect to be able to do with an object as a function implementer.

To that end, we’ll take a look at parameter passing from the perspective of the mutability (ability to be modified) of the parameters from both a caller’s and a function’s (callee’s) point of view...