Perfect Forwarding Forwards Objects Not Braced Things Trying To Become Objects -- Raymond Chen

By Blog Staff | Aug 25, 2023 02:43 PM | Tags: None

In C++, perfect forwarding is the act of passing a function’s parameters to another function while preserving its reference category. It is commonly used by wrapper methods that want to pass their parameters through to another function, often a constructor.

Perfect Forwarding Forwards Objects, Not Braced Things That Are Trying To Become Objects

By Raymond Chen

From the article:

In C++, perfect forwarding is the act of passing a function’s parameters to another function while preserving its reference category. It is commonly used by wrapper methods that want to pass their parameters through to another function, often a constructor.

template<typename T, typename... Args>
std::unique_ptr<T> make_unique(Args&&... args)
{
    return std::unique_ptr<T>(
        new T(std::forward<Args>(args)...));
}

The make_unique function takes its parameters, forwards them to the T constructor, and then puts the pointer to the newly-constructed T inside a unique_ptr. Those parameters are forwarded perfectly into the constructor: If the original parameters were rvalue reference, then the constructor receives rvalue reference. If the original parameters were lvalue references, then the constructor receives lvalue reference.

But the catch is that it can forward only objects. It can’t forward “braced things that are trying to become objects”.

C++ exceptions and memory allocation failure -- Wu Yongwei

By Wu Yongwei | Aug 24, 2023 10:45 AM | Tags: None

C++ exceptions are habitually disabled in many software projects. A related issue is that these projects also encourage the use of new (nothrow) for fear of exceptions. Is it good practice or bad practice? Also, how likely are we to really encounter out-of-memory errors? I will investigate on this topic and discuss strategies to deal with memory issues.

C++ Exceptions and Memory Allocation Failure

By Wu Yongwei

From the article:

In fact, every time we initialize or modify a string, vector, or map, we may be allocating memory on the heap. If we think that new will end in an exception (and therefore choose to use new (nothrow)), exceptions may also occur when using these mechanisms. In a program that has disabled exceptions, the result will inevitably be a program crash.

Ignoring abnormal scenarios like allocating more memory than the physical memory size at a time (which would likely be a logic error in the program), can a reasonable program still experience memory allocation failures?

C++23: static operator() and static operator[] -- Sandor Dargo

By Blog Staff | Aug 23, 2023 02:03 PM | Tags: None

In this article, we are going to review two new features of C++23. Now the language allows the call operator (operator()) and the subscription operator (operator[]) to be static.

C++23: static operator() and static operator[]

By Sandor Dargo

From the article:

static operator()

As we saw earlier in our big C++ algorithms tutorial, function objects are extensively used in the standard library to customise the behaviour of several functions. With the introduction of ranges in C++20 (and of earlier non-standard libraries), the usage of function objects became even more widespread.

Many function objects are extremely simple. Let’s take an implementation of isEven.

auto isEven = [](int i) {return i % 2 == 0;};

2023-08 Mailing Available

By Administrator | Aug 23, 2023 09:54 AM | Tags: None

The 2023-08 mailing of new standards papers is now available.

C++23: Syntactic Sugar with Deducing This -- Rainer Grimm

By Blog Staff | Aug 21, 2023 01:57 PM | Tags: None

The Curiously Recurring Template Pattern (CRTP) is a heavily used idiom in C++. It is similarly resistant to understanding as the classic design pattern visitor I presented in my last post: “C++23: Deducing This“.  Thanks to deducing this, we can remove the C and R from the abbreviation.

C++23: Syntactic Sugar with Deducing This

By Rainer Grimm

From the article:

CRTP

The acronym CRTP stands for the C++ idiom Curiously Recurring Template Pattern and denotes a technique in C++ in which a class Derived is derived from a class template Base. The critical point is that Base has Derived as a template argument.

template <typename T>
class Base{
    ...
};

class Derived : public Base<Derived>{
    ...
};

CRTP is typically used to implement static polymorphism. Unlike dynamic polymorphism, static polymorphism happens at compile time and does not require an expensive run-time pointer indirection.

Introduction to Programming with C++ For Engineers, Book Review -- Bartlomiej Filipek

By Bjarne Stroustrup | Aug 18, 2023 01:52 PM | Tags: None

Lots of practical examples, general programming, software development techniques, OOP, parallel algorithms, plus C++ to combine it all into working applications. This is a short introduction to the book “Introduction to Programming with C++” by Prof. Boguslaw Cyganek, an excellent book for students who start their journey with system coding.

Introduction to Programming with C++ For Engineers, Book Review

By Bartlomiej Filipek

From the review:

“I have been highly impressed by Introduction to Programming with C++ for Engineers and can’t recommend it enough. With its content designed keeping in mind the author’s own students, the book assumes no prior programming experience, making it an excellent choice for anyone who wishes to learn C++ as their first programming language. […]
The book extends its reach beyond just the programming language, shedding light on aspects such as microprocessor operations, software development processes, UML, and more. Furthermore, the appendices cover essential tools like CMake and Git, making this book a comprehensive guide for anyone delving into C++ programming. The detailed content, careful attention to detail, and clarity in explaining concepts have garnered much praise for the book. This makes it an invaluable resource for those aspiring to learn and understand modern C++ programming."

Let's Enumerate the UB -- Shafik Yaghmour

By Blog Staff | Aug 16, 2023 01:46 PM | Tags: None

Some time ago I started working on P1705 Enumerating Core Undefined Behavior, I have collected a large set of undefined behavior (UB) during that time. There is going to be a lot of work involved in getting the annex into shape and editing it into the standard. While this work is ongoing, I will take some time to write blog posts to explore the set of undefined behaviors.

Let's Enumerate the UB

By Shafik Yaghmour

From the article:

In these posts I will cover: why we have each undefined behavior, some consequences of running afoul of each UB and tools we can use to catch UB. My plan is to enumerate them in the order they appear in the standard.

IFNDR (What is that?)

Before we go on, let’s talk about a term we find in the standard, ill-formed no diagnostic required; also known as IFNDR. This is like undefined behavior in that the standard places no requirements on a program that contains IFNDR constructs, see [intro.compliance.general]p2.2 which says (emphasis mine):

If a program contains a violation of a rule for which no diagnostic is required, this document places no requirement on implementations with respect to that program.

compared to the defintion of undefined behavior which says:

behavior for which this document imposes no requirements

The main difference is that IFNDR is a static property of your code (it is a propety of the program).

C++23: Deducing This -- Rainer Grimm

By Blog Staff | Aug 14, 2023 01:39 PM | Tags: None

Anyone who thinks a small C++ standard follows a significant C++ standard is wrong. C++23 provides powerful extensions to C++20. These extensions include the core language, particularly the standard library. Today, I present a small but very impactful feature of the core language: deducing this.

C++23: Deducing This

By Rainer Grimm

From the article:

Deducing this, sometimes also called explicit object parameter, allows it to make the implicit this pointer of a member function explicit. Like Python, the explicit object parameter must be the first function parameter and is called in C++, by convention, Self and self.

struct Test {

    void implicitParameter();               // implicit this pointer
    void explictParameter(this Self& self); // explicit this pointer
};

Deducing this enables new programming techniques in C++23: deduplication of function overloading based on the object’s lvalue/rvalue value category and constness. Additionally, you can reference a lambda and invoke it recursively. Furthermore, deducing this simplifies the implementation of CRTP

How To Address 7 Major C++ Pain Points with CLion -- Anastasia Kazakiova

By Blog Staff | Aug 10, 2023 01:32 PM | Tags: None

In the 2023 Annual C++ Developer Survey conducted by the C++ Foundation, the community identified a number of major pain points when working with C++.

How To Address 7 Major C++ Pain Points with CLion

By Anastasia Kazakiova

From the article:

As we’ll discuss in this article, CLion can help C++ developers with most of these in various ways:

• Managing third-party libraries
• Improving build times
• Setting up a CI-pipeline
• Managing a CMake project
• Checking code for thread, memory and type safety issues on-the-fly
• Setting up a development environment from scratch
• Modernize your code

RFC - fat pointer class, evolution of YOMM2 -- Reddit Q&A

By Blog Staff | Aug 9, 2023 01:24 PM | Tags: None

Question from reddit poster: I am preparing to release a new feature, a fat pointer class (virtual_ptr), that makes method dispatch even more efficient. Dispatching a method with one virtual argument via a virtual_ptr takes only three instructions and two independent memory reads. As an interesting side-effect, it is now possible to use YOMM2 with non polymorphic classes hierarchies.

RFC - fat pointer class, evolution of YOMM2

From the discussion:

I am preparing to release a new feature, a fat pointer class (virtual_ptr), that makes method dispatch even more efficient. Dispatching a method with one virtual argument via a virtual_ptr takes only three instructions and two independent memory reads. As an interesting side-effect, it is now possible to use YOMM2 with non polymorphic classes hierarchies.

Once I increase the semantic minor version number, I will mostly be stuck with the API. So, if you are interested and in the mood, please review the documentation.

Beyond this, I have been mulling a major version bump. There are a few stuff that are deprecated, and I would like to get rid of them.

Also, I wonder if it would be a good time to switch to C++20. The internals would be a lot simpler and cleaner if I could use concepts.

I have a few major developments on the radar:I have a few major developments on the radar:

• dispatch on std::any and std::variant
• "fat" versions of std::any and std::variant (in the manner of virtual_ptr)
• going headers only
• related to the former: tunable runtime
• quasi static initialization of method tables

I wonder if it would be better to wait until these items are completed before switching to C++20 and putting the C++17 code in bugfix only mode.