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Providing a stable memory address to an external API

By Meeting C艹 | Mar 20, 2024 02:07 AM | Tags: performance meetingcpp intermediate experimental community C艹20 advanced

A post on how to provide a pointer to a Qt Model/View or other APIs storing pointers to their data without using shared_ptr or unique_ptr for the actual object.

Providing a stable memory address

by Jens Weller

From the article:

Some APIs allow you to store a pointer to your data element. This is used to access additional information from your types to display them in Model/View Architecture.

A while ago I showed how you can implement a tree with shared_ptr and enable_shared_from_this and then display this in QTreeView. And when working on my current project I knew this problem would come around again. Maybe not for a tree and a tree view, but I'll clearly need to have some way to have ui panels display and edit my data classes and store a stable memory adress as a pointer in Qt models. Back in 2015 the Qt5 example still used a pointer allocated with raw new for this, in Qt6 the example uses unique_ptr. Using shared_ptr for this back in 2015 was a good decision, and the code works very well. For the moment I don't see that my current project would need to make use of enable_shared_from_this, so using unique_ptr would be a good option...

 

 

Releasing the keynotes of Meeting C艹 2023

By Meeting C艹 | Dec 30, 2023 03:38 AM | Tags: performance meetingcpp intermediate community C艹20 C艹17 C艹14 basics advanced

Highlighting the current video releases for Meeting C艹 2023: the keynotes

With this year Meeting C艹 had a unique set of keynotes, covering 6 impossible problems for software devs with the opening keynote by Kevlin Henney, followed by great wisdom about how open communities thrive by Lydia Pintscher. The closing keynote by Ivan Čukić was an impressive medley composing various idioms with Prog(ressive) C艹.

All these keynotes are worth watching, a great contribution to our knowledge base as a community. Thanks to Kevlin Henney, Lydia Pintscher and Ivan Čukić for preparing these great presentations!

Merging intervals in next-gen C艹--Marco Arena

By Marco Arena | Mar 8, 2023 04:36 AM | Tags: thatsarotate ranges experimental C艹20 advanced

Revisiting a classical programming puzzle in next generation C艹:

Merging intervals in next-gen C艹

by Marco Arena

From the article:

A few weeks ago, I set this problem at Coding Gym: given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input...

About conditional breakpoints

By Meeting C艹 | Aug 18, 2022 07:11 AM | Tags: performance intermediate debugging debug basics advanced

A post on conditional breakpoints, including two surveys about their usage.

About conditional brealkpoits

by Jens Weller

From the article:

A few weeks ago someone asked me for advice on finding a specific bug in a larger C艹 code base...

I don't remember much of the details, but one of the challenges was that at least some of the code based used public members, and in order to find the bug a change in these members is what they wanted to understand. Adding out put statements into a setter function wasn't possible, as the code did not have those. My suggestion was using a conditional breakpoint. And it also made me curious, if and how they're used with in our community.

Talks and Speaker for Meeting C艹 2022 released

By Meeting C艹 | Aug 11, 2022 02:19 AM | Tags: meetingcpp intermediate conference community C艹20 C艹17 basics advanced

Since yesterday its possible to have a first look at the program of Meeting C艹 2022

A first view on the talks and speakers of Meeting C艹 2022

by Jens Weller

From the article:

I'm excited to release this update for Meeting C艹 2022: the talks and speakers for this years conference!

As you can see in the talk listing, this is still an ongoing process, getting the speaker pictures from the new speakers for this year will still take a while. Creating the schedule will also take a few weeks, as of now Tracks A and B are planned on site, with Tracks C and D being part of the online part.

Pass-by-value vs Pass-by-reference--James Mitchell

By Adrien Hamelin | Jul 22, 2022 01:21 PM | Tags: advanced

Complex world.

Pass-by-value vs Pass-by-reference

by James Mitchell

From the article:

Let’s dig into the age old question, should you pass-by-value or pass-by-reference in C艹? (or by pointer in C)

This blog post is mostly a re-post of a reddit comment that I made on r/cpp about pass-by-value and pass-by-reference, with some minor improvements, to make it easier to reference and save.

The answer isn’t as easy as it might seem, it depends on the Application Binary Interface (ABI) and your use-cases, there isn’t a one size fits all answer, this is even more the case for anything which is built to be cross platform.

First it’s probably good to break the problem down into two parts (focusing solely on performance, ignoring readability and maintainability which should often be more important)

  • The language construct costs (copying, moving, etc)
  • Compiler implications (aliasing, pointer provenance, etc)
  • The ABI (the stack, registers, etc)...

Assignment for optional--Barry Revzin

By Adrien Hamelin | Jun 7, 2022 01:19 PM | Tags: advanced

Highly non trivial.

Assignment for optional<T>

by Barry Revzin

From the article:

Let’s talk about assignment for optional<T>. I realize this is a fraught topic, but I want to try to build up proper intuition about how assignment has to work, especially since the debate around this topic has been fairly underwhelming. This post will almost exclusively discuss copy assignment (i.e. the one that takes an optional<T> const&), since everything just follows from that...

Zero-cost exceptions aren’t actually zero cost--Raymond Chen

By Adrien Hamelin | Mar 21, 2022 12:19 PM | Tags: advanced

The devil is in the details.

Zero-cost exceptions aren’t actually zero cost

by Raymond Chen

From the article:

There are two common models for exception handling in C艹. One is by updating some program state whenever there is a change to the list of things that need to be done when an exception occurs, say, because a new exception handler is in scope or has exited scope, or to add or remove a destructor from the list of things to execute during unwinding. Another model is to use metadata to describe what to do if an exception occurs. There is no explicit management of the state changes at runtime; instead, the exception machinery infers the state by looking at the program counter and consulting the metadata...