C++ - TopAnswers

TopAnswers C++

टेक्-मराठी

define an object with different subclasses in an if-statement

Trevor Trevor

0 You need to mark your `print` method `virtual`:

Anonymous 11738

golf coding fizz buzz 1

AryanXdProYT AryanXdProYT

Embed OpenCV SVM as preinitialized static variable 10

Somebody Somebody

3 Unfortunately, OpenCV does not have a setter for the decision function and the support vectors, which does not allow me to inject my own loader.

Somebody

Does std::get_time require leading zeros for numbers? 5

GreenDragon GreenDragon

4 It's indeed an old bug in gcc - [Facet time_get not reading dates according to the IEEE 1003 standard](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45896).

GreenDragon

How to suppress command line warning in Visual Studio?

Anonymous 1317 Anonymous 1317

1 It seems you can't suppress D-warnings by design, but I can't find this in the Microsoft documentation. It is said by various people on the internet, for example https://stackoverflow.com/questions/14640690/how-to-suppress-d9025-warning-in-microsoft-c-build-tools

Anonymous 1317

Is There a Cross-Platform Implementation of std::experimental::is_detected?

Jonathan Mee Jonathan Mee

2 A possible implementation of `std::experimental::is_detected` is available here: https://en.cppreference.com/w/cpp/experimental/is_detected#Possible_implementation

Jonathan Mee

Derived method is hiding the base one, how to access the base method? 3

GreenDragon GreenDragon

2 Using syntax `[OBJECT].[BASE_CLASS]::[METHOD]`

Pax

Using modules from Visual Studio 2019 Developer Command Prompt 4

GreenDragon GreenDragon

2 As described [here](https://devblogs.microsoft.com/cppblog/c-modules-conformance-improvements-with-msvc-in-visual-studio-2019-16-5/), you need to compile with two options:

JHBonarius

Why Were Range Access Functions Provided in C++?

Jonathan Mee Jonathan Mee

2 The [stated motivation](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4017.htm) for the inclusion of these functions in the standard was to:

Jonathan Mee

Should I Prefer Declaring a Variable as a const char* or a const char[]? 3

Jonathan Mee Jonathan Mee

2 The simple answer is that when declaring a variable you should prefer a `const char[]`.

Jonathan Mee

chat

transcript

Jack Douglas replying to Anonymous 5566

good question - we don't really have a home for it I'm afraid!

Anonymous 5566

Hi. I posted a Vulkan question on SO yesterday. That's completely unrelated to you, but I suddenly came to think of Codidact, and that I made an account long ago. Now I wonder, if I was to ask that question here, on which subsite would I post it? My Vulkan question is not constrained to a particular language, so where would it go?

AryanXdProYT

i need help , can you tell me the best code for fizz buzz program for golf coding

Jonathan Mee

@GreenDragon that's definitely a good article. I work at EA and someone linked it there earlier and I really enjoyed the read.

GreenDragon

[Don’t blindly prefer emplace_back to push_back](https://quuxplusone.github.io/blog/2021/03/03/push-back-emplace-back/)

निरंजन replying to Jack Douglas

[Thanks.](https://topanswers.xyz/c?q=1399)

Jack Douglas replying to निरंजन

https://topanswers.xyz/c

निरंजन

Okay, I will open a question when the community is formed :)

Jack Douglas

and C is a big topic so could eventually build it's own momentum

Jack Douglas replying to निरंजन

it's a start!

निरंजन

I have a question, but of course only one question might not be sufficient for a community :)

Jack Douglas replying to निरंजन

No I think we need a C community for that — and I think we should have one if there is any prospect of getting questions

निरंजन

Are `C` questions allowed here?

GreenDragon

[A Concurrency Cost Hierarchy](https://travisdowns.github.io/blog/2020/07/06/concurrency-costs.html) - excellent article

Jack Douglas

there are no technical obstacles, it's just a question of UI and a few minor quandries

Jack Douglas

we are working on making it easy to add these to posts

GreenDragon

cool

Jack Douglas

::: tio Hcq9CoAgEADg/Z7isqWGoFmluTdollNC8A87p@jZLfrmj0pZTqLeR58oNOtQ@3xxdSZuAD4xRuPTNOMN@LnYSkm5MWqNYnchZDxyDXYQ6g/VcasJVwVP7y8
§§§ text/x-c++src cpp-gcc
#include <iostream>

int main() {
    std::cout << "Hello World!";
    return 0;
}
§§§
``` none
Hello World!
```
:::

Jack Douglas

I've added most of those, and I'll chew over the rest :)

GreenDragon

I guess it is `boost`, `multithreading`, `ranges`, `qt` , `network-programming or just networking` ... so it should be or specific widespread library or specific area maybe `stl`/ `C++20` / `templates`. I'm also not fun about `string` or `arrays` tags. 
Maybe special tag `homework`.

Jack Douglas replying to GreenDragon

true, but if there are tags you are sure we will need later, please mention them and we'll add them in advance

GreenDragon

It's not important so far there are few questions.

GreenDragon

not yet. I used only several tags on SO to subscribe to RSS for new questions.

Jack Douglas replying to GreenDragon

have you thought about what tags will be for in this community? SE goes a bit mad with tagging, and I think it's best to add only 'useful' tags, i.e. things that people will likely want to filter a search on

Jack Douglas

::: quote 1 44044 1027 219,219,219 131,133,133
GreenDragon *— 8 hours ago* *in [The Tavern](/meta?room=1#c44044)*  
>Default control for tag is too narrow - ![tA1.jpg](/image?hash=9d0770c69cf7e51c06b17150e19fcdcfff5cde1a2c298e3b85c4f3cd753aa2a6)
:::

GreenDragon

me neither =)

Jack Douglas replying to GreenDragon

that does sound more likely to work but I'm no C++ expert :)

GreenDragon

Well after a bit re-thinking, really this can be adopted to wide question about specific concept itself, so it will be valid. 
"Message passing between threads" (as common question) and "How Golang-channels can be implemented in C++" (and in the answers will be good to provide link for some OS libraries for illustration).  But ... sometimes it's not always obvious and initial version of Q may be like "Channels in C++ how?" or something like that.

GreenDragon

Yup, I am not talking about stuff like GUI (there are enough awesome lists on Github),  only about rarely cases that could be interesting people with experience in other programming languages.

Jack Douglas replying to GreenDragon

generally we want questions that lend themselves to one or two good answers, just like on SE — "what library that implements this concept" is generally unlikely to be that kind of question in general, but it may depend on the particular concept…

GreenDragon

Are questions about libraries appropriate here? For example some time ago I was re-writing some application from Go where used channels. Therefore I wanted to find a library that implement this very useful concept. Quick search on Github gave me some options but other hosting service like Gitlab or less popular (like sourcehut that in alpha stage now) haven't good search mechanism (maybe yet but still). 

And of course some comments about use cases would be useful as well.

Jack Douglas replying to GreenDragon

thanks, it is good to know that!

GreenDragon

Definitely - big stuff like concepts, coroutines, modules, ... and many many small things.

Jack Douglas replying to GreenDragon

is it a major update to the language then?

GreenDragon

And C++20 also beget many totally new questions ;-)

Jonathan Mee

Not that I'm a C++20 whiz, but I enjoy the opportunity to study and learn.

Jonathan Mee

The exciting thing is that C++20 is bringing changes to a lot of the common answers. Rather than blindly importing we're really able to improve in a lot of cases.

Jack Douglas

We are also free to import selected content from SO if you think that would be good to do in parallel

Jonathan Mee

By helpful I mean, helpful to flesh out the backlog of available content on the site.

Jonathan Mee

I believe that would be helpful. I'd be happy to assist in answering them where I'm able.

Hosch250

I'm not enough of a C++ user to write Q/A posts, but I've had enough exposure to do a set of Q's, I think.

Hosch250

For example, I could ask how to write a safe copy constructor, or how to correctly open, read/write, and close a file.

Hosch250

Would it be appropriate to ask "basic" questions that I could find the answers to elsewhere on the web?

Jonathan Mee

<3

Jack Douglas

it does look like we are free to use it — I've switched it over

Jack Douglas replying to Adám

I thought it required attribution — not sure which Wikipedia page I got that impression from now…

Adám

Any reason not to use [the official C++ logo](https://github.com/isocpp/logos) for this chat room (and the site)?

Skillmon replying to Jack Douglas

I saw that one, that's why I got here. As an aside, the notification for this message was missing the link to the room when I got it. Not sure how to reproduce, when I changed the room (there was another notification) this one got the link.

Jack Douglas replying to Skillmon

::: quote 218 19302 ba1d6fd8881a87067fe28d71a5ddc594f0146228d32fe77a6399565d3b928bd8 219,219,219 131,133,133
Jack Douglas *— an hour ago* *in [I'd like a new community on TopAnswers. How do I go about making that happen?](/meta?room=218#c19302)*  
>OK @Jonathan, let's give it a go: https://topanswers.xyz/cplusplus — thanks for the vote of confidence and for your enthusiasm — we'll continue to try and encourage others to participate, but if there is reasonably regular activity in there I think it's likely that we'll gradually get people joining. Perhaps even a few from reddit :)
:::

Skillmon

Something new!