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November 2024

C++ programmer's guide to undefined behavior: part 10 of 11

By Andrey Karpov | Nov 29, 2024 01:09 AM | Tags: vla virtual functions variable length arrays uninitialized variables undefined behavior trivial types odr violations c++20 unbounded ranges abi

Your attention is invited to the tenth part of an e-book on undefined behavior. This is not a textbook, as it's intended for those who are already familiar with C++ programming. It's a kind of C++ programmer's guide to undefined behavior and to its most secret and exotic corners. The book was written by Dmitry Sviridkin and edited by Andrey Karpov.

C++ programmer's guide to undefined behavior: part 10 of 11

by Dmitry Sviridkin

From the article:

As you can see from the backtrace, the problematic object whose destructor caused the crash was a vector of strings in libgtest.so. In GTest sources, I found that this vector is a global variable where InitGoogleTest() stored recognized command line arguments. It's just a global variable declared in the compiled file and not presented in the header file. All seemed fine, except for one detail: it wasn't marked as static and was not wrapped in an anonymous namespace. So what? It worked, didn't it? Yeah, it worked. The trick was how the gMock library is built. Let's reproduce it step by step.

What is the Current Time Around the World? -- Bartlomiej Filipek

By Blog Staff | Nov 28, 2024 12:46 PM | Tags: None

2024-11-21_12-48-43.pngIn this blog post, we will explore handling dates using std::chrono, including time zones. We’ll utilize the latest features of the library to retrieve the current time across various time zones, taking into account daylight saving time changes as well. Additionally, we will incorporate new capabilities introduced in C++23, such as enhanced printing functions and more.

What is the Current Time Around the World? Utilizing std::chrono with Time Zones in C++23

by Bartlomiej Filipek

From the article:

Let’s start with the following code that prints the current date and time:

#include <chrono>
#include <print>

int main() {
    auto now = std::chrono::system_clock::now();
    std::print("now is {}", now);
}

You can run it through Compiler Explorer

In my session, I’m getting the following results:

Now is 2024-11-01 11:44:06.374573703

Having Fun with Modern C++ -- Daniel Lemire

By Blog Staff | Nov 25, 2024 12:40 PM | Tags: None

Jb7DBcxe_400x400.jpgRecent versions of the C++ language (C++20 and C++23) may allow you to change drastically how you program in C++. I want to provide some fun examples.

Having Fun with Modern C++

by Daniel Lemire

From the article:

Thanks to the integration of the features from the popular fmt library, it is much easier to format strings elegantly in C++. In turn the fmt library was inspired by the work done in languages like Python.

Suppose that you have a vector of integers and you want to print its content:

std::vector<int> v = {1, 2, 3, 4, 5};
std::println("{}", v);

Suppose you want it to be centered in a line of 40 characters, with underscore characters around it:

std::vector<int> v = {1, 2, 3, 4, 5};
std::println("{:_^40}", v);
// ____________[1, 2, 3, 4, 5]_____________

CopperSpice: std::launder

By Ansel Sermersheim | Nov 25, 2024 11:26 AM | Tags: None

New video on the CopperSpice YouTube Channel:

std::launder

by Barbara Geller and Ansel Sermersheim

About the video:

Our recent C++ video started a lively conversation. We showed a use case for std::launder which caught several developers off guard. A new compiler setting was enabled which exposed a problem in our existing code. Please watch the full video to find out what we learned.

Take a look and remember to subscribe.

Trip Report: Meeting C++ 2024 -- Sandor Dargo

By Blog Staff | Nov 21, 2024 12:29 AM | Tags: None

SANDOR_DARGO_ROUND.JPGLast week, I got the chance to go to Berlin and participate in the 10th edition of Meeting C++ which is as far as I know the biggest C++ conference in Europe. Considering both the online and onsite participants, there were about 500 of us, eager to learn more mostly but not only about C++.

Trip Report: Meeting C++ 2024

by Sandor Dargo

From the article:

The conference was held in the East side of Berlin, in the Vienna House by Wyndham Andel’s Berlin Hotel offering some cool views of the city from its higher floors, especially from its sky bar. Not that we had a lot of time wandering in Berlin, the schedule was quite packed. Although the program only started around 9-10 AM depending on the day, the first two days the official program didn’t end before 10 PM.

Given the bit cold and cloudy weather, I realized that Berlin in November is really perfect for a conference. People will not be tempted to escape the venue for long walks outside. It just feels better to be inside.

C++ Compile-Time Programming -- Wu Yongwei

By Blog Staff | Nov 14, 2024 11:19 AM | Tags: None

logo.pngProgramming at compile time has been possible in C++ for a long time. Wu Yongwei considers its past, present and future.

Compile-time programming is a key feature of C++. It enables writing high-performance code often unattainable in other languages. This article explores its past, present, and future applications, highlighting the diverse possibilities in C++. We’ll briefly cover template metaprogramming, constexpr, variadic templates, static reflection, and more.

C++ Compile-Time Programming

by Wu Yongwei

From the article:

Compile-time programming is vastly different from run-time programming. The code runs during compilation, but the results can be used at run time.

Some believe compile-time programming is merely a trick, unused in real-world engineering. To them, I ask: do you use the C++ Standard Library? The mainstream implementations rely heavily on various programming techniques, including compile-time programming.

‘I don’t write the standard library’ – this might be a possible response. But consider this: the standard library is just one tool, a standard weapon. Is it enough to use only standard tools? That’s the real question.

The abundance of excellent open-source libraries suggests otherwise. A skilled programmer crafts tools for themselves and their team. If your work feels tedious, perhaps it’s time to build a bulldozer to tackle problems.

Compile-time programming offers a way to build such tools.

if constexpr requires requires { requires } -- Jonathan Müller

By Blog Staff | Nov 11, 2024 11:10 AM | Tags: None

thinkcelllogo.pngProbably the two most useful features added to C++20 are requires and requires. They make it so much easier to control overload resolution, and when combined with if constexpr in C++17, they allow basic reflection-based optimizations in templates. While requires requires has gotten a lot of (negative?!) press for controlling overload resolution, its cousin requires { requires } is a bit overlooked.

if constexpr requires requires { requires }

by Jonathan Müller

From the article:

C++20 added requires, a way to enable or disable a function overload based on some compile-time condition. For example, consider a facility for producing debug output of types for error reporting:
thinkcellconst.png

The two overloads with the requires clause are only enabled for integers or floating point types, respectively, and are not considered otherwise. Additionally, overload resolution is smart: It knows that we want the overload with the most specific requirements, and it will only pick the first function when no other overload matches. This is also where concept comes in: A concept is simply a way to name a group of requirements that affects the search for more specific requirements. The technical term for that is subsumption. Because creating named requirements with concept also comes with additional syntax sugar, you don't need requires—so this blog post is gonna ignore concept. In general, if you would use a concept in only one place, it is too early to introduce it.

C++ programmer's guide to undefined behavior: part 9 of 11

By Andrey Karpov | Nov 11, 2024 10:38 AM | Tags: undefined behavior static inline reserved names odr null pointer dereferencing nrvo

Your attention is invited to the ninth part of an e-book on undefined behavior. This is not a textbook, as it's intended for those who are already familiar with C++ programming. It's a kind of C++ programmer's guide to undefined behavior and to its most secret and exotic corners. The book was written by Dmitry Sviridkin and edited by Andrey Karpov.

C++ programmer's guide to undefined behavior: part 9 of 11

by Dmitry Sviridkin

From the article:

And you could write it only in C++. In C, however, this mess has been forbidden (see 6.5.3.2, note 104). Also, you can't use the dereference operator on invalid and null pointers anywhere in C. Meanwhile, C++ has its own, special way of doing things. These weird examples were built in constexpr context (let me remind you that UB is forbidden there, and the compiler checks for it).