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The Difference Between Undefined Behavior and Ill-formed C++ Programs -- Raymond Chen

By Blog Staff | Aug 30, 2024 01:48 PM | Tags: None

The C++ language has two large categories of “don’t do that” known as undefined behavior and ill-formed program. What’s the difference?

The Difference Between Undefined Behavior and Ill-formed C++ Programs

by Raymond Chen

From the article:

The C++ language has two large categories of “don’t do that” known as undefined behavior and ill-formed program. What’s the difference?

Undefined behavior (commonly abbreviated UB) is a runtime concept. If a program does something which the language specified as “a program isn’t allowed to do that”, then the behavior at runtime is undefined: The program is permitted by the standard to do anything it wants. Furthermore, the effect of undefined behavior can go backward in time and invalidate operations that occurred prior to the undefined behavior. It can do things like execute dead code. However, if your program avoids the code paths which trigger undefined behavior, then you are safe.

CppCon 2024 C++ Exceptions for Smaller Firmware -- Khalil Estell

By Blog Staff | Aug 29, 2024 03:14 PM | Tags: None

Registration is now open for CppCon 2024! The conference starts on September 15 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting some upcoming talks that you will be able to attend this year. Here’s another CppCon future talk we hope you will enjoy – and register today for CppCon 2024!

C++ Exceptions for Smaller Firmware

Tuesday, September 17 10:30 - 12:00 MDT

by Khalil Estell

Summary of the talk:

For years, developers have overlooked a powerful tool for reducing binary size: C++ exceptions. Join me on a deep dive into the world of exceptions and discover how they can be harnessed to create more space efficient firmware. We’ll explore the requirements and best practices of embedded development, and show what is required to use exceptions in that environment. By the end of this talk, you’ll have a thorough understanding of how exceptions are handled, what their space costs are, and how exceptions compare to functional errors as values.

Khalil is a ISO C++ Committee Member and has extensive experience writing production firmware.

CppCon 2024 An Ode to Concepts -- Nina Ranns

By Blog Staff | Aug 28, 2024 01:51 PM | Tags: None

An Ode to Concepts

Friday, September 20 09:00 - 10:00 MDT

by Nina Ranns

Summary of the talk:

Concepts are a long awaited C++ feature. They allow constraining a template in a much more elegant way than various enable_if tricks. In this lecture we cover the basics of concepts syntax, how to write a concept and how to apply a concept in your code. Then we look at one woman's experience of implementing a heavily constrained type before and after introduction of concepts.

Nina Ranns has been a member of the C++ standard committee since 2013, focusing mostly on the core part of the language, and committee secretary since 2018. Throughout her career she has worked for Siemens, Motorola, Datasift, and Symantec on everything from parts of the UMTS network to cloud based antivirus products. Currently an independent consultant with contracts for EDG, QT, and most recently Bloomberg, where she is eagerly extending her library knowledge and helping create new polymorphic-allocator friendly library types.

Once More About the Rule of 5 -- Sandor Dargo

By Blog Staff | Aug 27, 2024 01:40 PM | Tags: None

In a recent talk at C++OnSea, Arne Mertz highlighted common misuses of guidelines, including the Rule of Five. This discussion prompted me to reflect on a recurring pattern I've observed in C++ classes that explicitly default constructors and destructors, leading to unexpected behaviors with move semantics.

Once More About the Rule of 5

by Sandor Dargo

From the article:

Let’s first repeat what the rule of 5 says.

The Rule of Five tells us that if we need to define any of a copy constructor, copy assignment operator, move constructor, move assignment operator or destructor then we usually need to define all five.

Fair enough.

Have you ever seen classes where the default constructor and destructor are explicitly defaulted? Like this?

class SomeClass {
public:
    SomeClass() = default;
    ~SomeClass() = default;

    void foo();
private:
    int m_num{42};
};

First of all, that’s not the best idea. You can simply remove them. But let’s assume that you cannot remove the user-provided destructor for some reason. Maybe it’s not defaulted and it does something.

What does the famous Hinnant table tell us?

Reminder: CppCon 2024 Regular registration ends Friday, Late registration opens Saturday

By Blog Staff | Aug 26, 2024 09:14 AM | Tags: None

The opening keynote of CppCon 2024 is just 20 days away! The program has over 100 great talks and panels, and the five keynotes have been announced:

Monday, Herb Sutter. "Peering forward: C++'s next decade" (Sched)
Tuesday, Khalil Estell. "C++ Exceptions for smaller firmware" (Sched)
Wednesday, Amanda Rousseau. "Embracing an adversarial mindset for C++ security" (Sched)
Thursday, David Gross. "When nanoseconds matter: Ultrafast trading systems in C++" (Sched)
Friday, Daveed Vandevoorde. "Gazing Beyond Reflection for C++26"

If you're interested in savings, the Regular price for on-line and on-site tickets is available until this Friday, August 30. After that tickets will still be available right up to the conference, but at the late registration ticket price.

To register for CppCon 2024 at the Regular rate, click this link this week.

For details of on-line and on-site tickets, see the Registration page which includes information about student registration discounts, group rates, the CppCon Academy (extra pre- and post-conference classes by world-renowned instructors including online classes for those who can't be there in person), the community dinner, the "Meet the Presenters" banquet, and much more!

CppCon 2024 Back to Basics: Functional Programming in C++ -- Jonathan Müller

By Blog Staff | Aug 23, 2024 12:48 PM | Tags: None

Back to Basics: Functional Programming in C++

Thursday, September 19 09:00 - 10:00 MDT

by Jonathan Müller

Summary of the talk:

Functional programming is a declarative way of writing programs by composing functions.
In many situations, this can lead to code that is easier to write and understand and less error-prone.
However, it requires a shift to a more functional mindset.
This talk gives an introduction to functional programming in C++ using the modern standard library.
We will cover algorithms using `std::ranges`, composable error handling with `std::optional` and `std::expected`, algebraic data types, and separating IO from computation.
In the end, we'll even cover the M-word.

Jonathan is a Software Engineer at think-cell. There, he is responsible for maintaining think-cell's core libraries, which include a custom range library, a fast and convenient JSON parser, and many other utilities and data structures to write elegant C++ code. Before working at think-cell, he wrote many useful open-source C++ libraries. He is also a member of the C++ standardization committee, where he serves as the assistant chair for std::ranges, and a frequent conference speaker.

C++ programmer's guide to undefined behavior: part 4 of 11

By Andrey Karpov | Aug 23, 2024 07:45 AM | Tags: undefined behavior ub tuples lifetime extension lifetime lambda function

Your attention is invited to the fourth 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 4 of 11

by Dmitry Sviridkin

From the article:

In the C++98, the committee made a terrible decision that seemed reasonable at the time. They created a specialization for std::vector<bool>. Normally, sizeof(bool) == sizeof(char), but one bit is enough for bool. However, 99.99% of all possible platforms can't address memory one bit at a time. Let's pack bits in vector<bool> and store CHAR_BIT (usually 8) boolean values in one byte (char) for more efficient memory utilization. As a result, one needs to work with std::vector<bool> in a very special way...

CppCon 2024 Building Safe and Reliable Surgical Robotics with C++ -- Milad Khaledyan

By Blog Staff | Aug 22, 2024 12:45 PM | Tags: None

Building Safe and Reliable Surgical Robotics with C++

Wednesday, September 18 15:15 - 16:15 MDT

by Milad Khaledyan

Summary of the talk:

This talk examines the use of C++ in building distributed robotic surgical systems, emphasizing safety, performance, and reliability. While C++ offers strong performance benefits, it also presents challenges in meeting industry standards and regulations in the medical technology field. We discuss the architectural decisions and strategies employed to meet international safety standards for medical devices, and present techniques for writing efficient, safe and reliable software. Our experience in building a surgical robotic system serves as a case study, highlighting the challenges and solutions in this highly regulated domain.

Milad Khaledyan is a Staff Robotics Software Engineer at Johnson & Johnson MedTech, based in Santa Clara, CA, USA. With extensive experience across various companies, he specializes in software development for robotics in medical devices, as well as autonomous robots in manufacturing settings. Milad earned his doctoral degree in Mechanical Engineering, specializing in Robotics and Control, from Louisiana State University in 2018.

What's so hard about constexpr allocation? -- Barry Revzin

By Blog Staff | Aug 21, 2024 05:21 PM | Tags: None

Before C++20, constant evaluation couldn't handle allocations, causing any such attempts to fail. This changed with C++20, which introduced the ability to allocate memory during constant evaluation, although with strict limitations requiring deallocation during the same evaluation period. Despite these advancements, certain operations, such as declaring a constexpr std::vector, remain impossible, with the goal of this blog post being to explore why these limitations persist.

What's so hard about constexpr allocation?

by Barry Revzin

From the article:

Before C++20, we couldn’t have any allocation during constant evaluation at all. Any attempt to do so would fail the evaluation — it would no longer be constant.

In C++20, as a result of P0784R7, that changed. Finally we could do allocation during constant evaluation. However, this evaluation was extremely limited. Specifically, any allocation that happens must be deallocated during that constant evaluation.

This opened the door to a wide range of operations that weren’t possible before. We can now have local std::strings and std::vector<T>s! Those just work!

But we still cannot just declare a constexpr std::vector:
#include <vector> 
constexpr std::vector<int> v = {1, 2, 3}; // error 
And we cannot even declare a local constexpr std::vector in a consteval function:
#include <vector> 
consteval auto f() -> int { constexpr std::vector<int> v = {4, 5, 6}; // still error 
return v.size(); 
} 
This limitation still remains in C++23 and could very well still remain in C++26. The goal of this blog post is to explain why we haven’t just solved this problem already.

CppCon 2024 Leveraging C++20/23 Features for Low Level Ineractions -- Jeffrey Erickson

By Blog Staff | Aug 21, 2024 12:41 PM | Tags: None

Leveraging C++20/23 Features for Low Level Ineractions

Tuesday, September 17 14:00 - 15:00 MDT

by Jeffrey Erickson

Summary of the talk:

Low level interactions are a core part of embedded implementations. All too often, C++ developers rely on C constructs and interactions due to prior biases around language support. Herein we present effective leveraging of C++20 and C++23 constructs in an embedded driver code base. From using an existing C driver more effectively with modern C++ smart pointers to leveraging constexprs for bit and byte manipulation in the standard library, we will go over how you can stay on the cutting edge of the C++ language evolution in the embedded space.

Jeffrey E Erickson works in HW/SW Codesign Architecture at Altera, an Intel company. He holds a BS in Electrical and Computer Engineering from the University of Virginia and a doctorate from Rutgers University and UMDNJ. For 15 years he has worked in embedded systems development including FPGA-processor integration, secure firmware development, and systems modeling. He holds 3 patents in image processing and signal integrity.