-
Stay up-to-date with everything C++! Content directly fetched from the subreddit just for you. Join our group for discussions : @programminginc Powered by : @r_channels
An Extensive Benchmark of C and C++ Hash Tables
https://jacksonallan.github.io/c_cpp_hash_tables_benchmark
https://redd.it/1d418aw
@r_cpp
Most stupidly simple bug you encountered?
three days ago in my soydev project I had a function like this
template<typename Fn>
void addCallback(Fn fn){...}
template<typename Fn>
void execute(Fn fn) {
auto res = fn(this,keycode);
....
....
....
if(res == nullptr) return
addCallback(fn);
}
How hard is it to land a C++ job?
I know it’s very vague and that multiple factors play a role in whether you are hired or not but I’m curious on your opinions on how hard it’s to get a c++ remote job for junior developer with no prior experience
https://redd.it/1d3nskf
@r_cpp
Lambda capture case
Hi. I’m trying to figure out one corner case where my testcase is as follows:
Class Hello
{
Public:
Int x, y;
Std::function<bool()> cond;
Hello()
{
Auto lam1 = this () { return x < y; };
Auto lam2 = & () { return lam1(); };
Cond = lam2;
}
Void run()
{
If( cond() )
{
Std::cout << “Sampled” << std::endl;
}
Else
{
Std::cout << “Not sampled” << std::endl;
}
}
};
Int main()
{
Hello h;
h.x = 10;
h.y = 20;
h.run();
h.x = 20;
h.y = 10;
h.run();
Return 0;
}
On running this code, the expected output should be:
Sampled
Not Sampled
But I’m getting garbage values in x and y and the output is not matching the expected output.
Can someone please explain what’s the problem here ?
https://redd.it/1d3lgfl
@r_cpp
HPX 1.10.0 Released! – The STE||AR Group
https://hpx.stellar-group.org/hpx-1-10-0-released/
https://redd.it/1d3im28
@r_cpp
An idea for course generation
Hey everyone.
I made an open-source AI course generator with NextJS and Gemini Pro. I tried both OpenAI and Gemini, and I liked the writing of Gemini better. (I might implement the OpenAI API too)
Cat++ is an experimental AI-powered C++ course generator that explores the future of personalized learning.
Before you tell me the obvious: the code can be inaccurate, it can have bad practices and a lot of mistakes, yes I am aware of that. This is a proof-of-concept project. But with AI improving, this is just a concept what is possible in the future. How it works:
Provide a prompt like
Generate a JSON array representing a C++ curriculum for memory management.
and it will dump out some topics that will be on the sidebar, then you run the content generator with the pre-defined template, and it will give you a course tailored for your specifics.
https://github.com/skillman1337/cat-plus-plus/raw/main/showcase/desktop\_page.png?raw=true
https://github.com/skillman1337/cat-plus-plus/raw/main/showcase/mobile\_page.png?raw=true
I had fun with generating topics in different tones, writing styles, templates etc... the possibilities are endless.
It's fully responsive and it's purely just for fun. I hope AI will improve to the point that we have bigger context length, more accuracy, and I hopefully my application can give some ideas on what is possible with combining some webdev and AI.
Link to the project: https://github.com/skillman1337/cat-plus-plus/
https://redd.it/1d3c0ku
@r_cpp
Memory Arenas talk
Hi everyone, I found this in the C group on Reddit, and thought you may enjoy this talk as much as I did. What's particularly nice is the extensive Q&A at the end.
https://www.rfleury.com/p/enter-the-arena-talk
https://redd.it/1d2ysd9
@r_cpp
Workflow v0.11.4 Released, Easier to Express Selection Semantics by Asynchronous Tasks in Concurrency.
It has been 2 years past since last post. So here let me add some background information here : Workflow is a C++ Parallel Computing and Asynchronous Networking Engine, which we have spent nearly 4 years developing and maintaining.
Using C++ to better express concurrency semantics is the dream of every C++ developer. Workflow uses asynchronous tasks with simple interfaces and efficient internal resource management to combine the calculations and networks.
Recently, it also supports selection semantics for concurrency, which can achieve correct branch processing and perfect resource recycling in concurrent scenarios. Hope you are interested.
Reference: https://github.com/sogou/workflow/releases/tag/v0.11.4
# New Features
* Add WFSelectorTask.
* Support setting DNS message's records. Enable users to make a fully functional DNS server by using WFDnsServer.
* Enable setting specific SSL_CTX for each network task.
* WFMySQLConnection and WFKafkaClient enable setting a specific SSL_CTX.
* JSON parser adds 'json_value_copy()'.
# Improvements
* More compatible with some rediculous HTTP server.
* Simplify Communicator's codes.
# Bug Fixes
* Fix bug when creating a client task with IPv6 address string.
* Fix kafka client bug when a broker is IPv6.
* Fix DNS parser potensial recursive bug.
You may also refer to issues:FAQs for more interesting usages
https://redd.it/1d2p5ox
@r_cpp
Accepting presentation proposals for C++ Boston Meetup
Presentation proposals are open for C++ Boston Group!
We are accepting presentation proposals for future meetups! Do you have something awesome to share? Best practices that you feel others may benefit from? Please submit your proposal below and we will take it into consideration for upcoming meetups!
https://forms.gle/uSXitfPWBzV525NR9
https://redd.it/1d2kcia
@r_cpp
https://github.com/serge-sans-paille/frozen
- ...
Updates - https://x.com/krisjusiak/status/1795433288271552557, https://x.com/krisjusiak/status/1795430660049617219
https://redd.it/1d2j4pv
@r_cpp
Will modules become a cargo/crates for cpp?
In r/rust (OP: https://www.reddit.com/r/rust/comments/1d2d5ub/howmuchworkwouldbeinvolvedtousecargoforc/) somebody asked whether it is naive to think that you can make cargo/crates work for cpp (without destroying crates altogether).
One of the responses was: "Yes, laughably naive. You’ll find that the C++ language specification leaves everything wide open; it doesn’t define packages in any way. Headers just show up somehow, and the language spec doesn’t care how. As a result, every possible way of installing and finding headers and libraries is already in use, and a package manager would have to accommodate all of them. Good luck with that nonsense. Oh, and don’t forget that C++20 modules make the problem even worse."
Since the OP was in r/rust (I am not the OP), I wanted to hear what cpp people thought on this, both whether rust's actual package management system could be transplanted to cpp and/or whether modules remedy the problems some/many people have with cpp in terms of headers or whether they have just made things worse.
https://redd.it/1d2i2j7
@r_cpp
Worst implicit casting in C++
Guy talks about implicit casting in C++ in this video and shows some ways in which he corrects some mistakes https://www.youtube.com/shorts/hVjvo\_cXHrU
https://redd.it/1d2evcv
@r_cpp
Can any body tell me what is happening in this case?
int& value(int& x){
x=19;
return x;
}
int main(){
int y=10;
std::cout<<y<<"\\n";
value(y)=0;
std::cout<<value(y)<<"\\n";
return 0;
}
to my knowledge this code should return
10
0
why is it returning
10
19
(chat gpt is also saying that the answer should be my answer )
compiler(g++)
https://redd.it/1d2aqe5
@r_cpp
Where do I start
I have no idea how to code and really want to start, I just don't know what to do. Any advice? Thanks.
https://redd.it/1d22tk1
@r_cpp
C++ f string equivalent when
Why is there no f string equivalent like in python, or $ in C# in cpp?!?!?!
https://redd.it/1d1uqbt
@r_cpp
New to programming
I have no prior experience with programming languages. People keep telling me I need to learn c first before c++ which sounds like bs. Some also told me to learn python since it's easier than c++ and can make me confident in learning it. My focus is to be a professional level game developer that can earn lots of money from AAA companies (though money ain't the only thing that matters to me) and become a good indie game developer for myself afterwards. Do i need to learn all c++ or only some of it is revelent in game development. I need suggestions for resources both free and paid. Though I would only buy the udemy ones since they're really cheap and don't break the bank like Coursera does.
https://redd.it/1d3xtlh
@r_cpp
The Visual Studio compiler is confused by default function parameters
I was working on adding support for allocators in the boost utf_to_utf conversion functions and I managed to confuse the compiler by omitting the optional function parameters when calling boost::locale::conv::utf_to_utf<char32_t, char, std::allocator<char32_t>>("hello world");
It tries to compile std::basic_string<char, std::char_traits<char>, std::allocator<char32_t>> and fails because that is invalid.
It does however work when you call it with all parameters: boost::locale::conv::utf_to_utf<char32_t, char, std::allocator<char32_t>>("hello world", boost::locale::conv::default_method, std::allocator<char32_t>());
This is the weirdest compiler bug I've seen, how can it be confused by default parameters? Those have existed for longer than I have existed.
This is the modified boost code:
namespace boost { namespace locale { namespace conv {
/// \addtogroup codepage
///
/// @{
/// Convert a Unicode text in range begin,end) to other Unicode encoding
///
/// \throws conversion_error: Conversion failed (e.g. \a how is \c stop and any character cannot be decoded)
template<typename CharOut, typename CharIn, typename TAlloc = std::allocator<CharOut>>
std::basic_string<CharOut, std::char_traits<CharOut>, TAlloc> utf_to_utf(const CharIn* begin, const CharIn* end, method_type how = default_method, const TAlloc& alloc = TAlloc())
{
std::basic_string<CharOut, std::char_traits<CharOut>, TAlloc> result(alloc);
result.reserve(end - begin);
std::back_insert_iterator<std::basic_string<CharOut, std::char_traits<CharOut>, TAlloc>> inserter(result);
while(begin != end) {
const utf::code_point c = utf::utf_traits<CharIn>::decode(begin, end);
if(c == utf::illegal || c == utf::incomplete) {
if(how == stop)
throw conversion_error();
} else
utf::utf_traits<CharOut>::encode(c, inserter);
}
return result;
}
/// Convert a Unicode NULL terminated string \a str other Unicode encoding
///
/// \throws conversion_error: Conversion failed (e.g. \a how is \c stop and any character cannot be decoded)
template<typename CharOut, typename CharIn, typename TAlloc = std::allocator<CharOut>>
std::basic_string<CharOut, std::char_traits<CharOut>, TAlloc> utf_to_utf(const CharIn* str, method_type how = default_method, const TAlloc& alloc = TAlloc())
{
return utf_to_utf<CharOut, CharIn, TAlloc>(str, util::str_end(str), how, alloc);
}
/// Convert a Unicode string \a str other Unicode encoding
///
/// \throws conversion_error: Conversion failed (e.g. \a how is \c stop and any character cannot be decoded)
template<typename CharOut, typename CharIn, typename TAlloc>
std::basic_string<CharOut, std::char_traits<CharOut>, typename std::allocator_traits<TAlloc>::template rebind_alloc<CharOut>> utf_to_utf(const std::basic_string<CharIn, std::char_traits<CharIn>, TAlloc>& str, method_type how = default_method)
{
return utf_to_utf<CharOut, CharIn, typename std::allocator_traits<TAlloc>::template rebind_alloc<CharOut>>(str.c_str(), str.c_str() + str.size(), how, typename std::allocator_traits<TAlloc>::template rebind_alloc<CharOut>(str.get_allocator()));
}
/// @}
}}} // namespace boost::locale::conv
[https://redd.it/1d3npld
@r_cpp
A graphical depiction of the steps in building a C++ executable, basics
https://devblogs.microsoft.com/oldnewthing/20240529-25/?p=109818
https://redd.it/1d3o6gt
@r_cpp
Tools for End to End testing of a command line C++ program
Hey, I'm trying to run some e2e tests that replicate the user's interaction with the command line and compare the console output with the expected output. Therefore, it should actually interact with the terminal and read the outputs.
I guess I could just make some simple code for that, maybe even a bash script would do, but if there are already any tools for it (I haven't found any so far), it'd be great.
https://redd.it/1d3j2yw
@r_cpp
Fast Development Tools/Methods?
What plugins or tools for which IDEs do every day people use for C++? I'm currently coming back to it, and I find it strange I haven't come across some nifty speed increases.
The main thing I wish, was there to be pre-compile annotations like Lombok for Java. Yes, it's a little 'eh' but there's a deLombok feature for release builds. @Getters/@Setters are just nice. @Builders too.
I've seen a lot of headache over "header-only" builds. Seems to be fine for what I'm doing. Im using Qt, so not always avoidable. A nice refactoring tool doesn't seem to be showing up anywhere though? Be nice to just have a combined file type, and let the IDE index changes and auto produce appropriate h/cpp files to avoid linker confusion down the road.
I know C++ might get reflection in the upcoming new feature releases 45 years from now, but a lot of this could be handled like preprocessor commands I'd think.
PS: Yes. I know I'm probably having some legacy C++ devs fuming right now. I just want to have faster development times on personal side projects. Sharing libraries or enterprise level code isnt on the table right now.
https://redd.it/1d3etmi
@r_cpp
C++23: chrono related changes
https://www.sandordargo.com/blog/2024/05/29/cpp23-chrono
https://redd.it/1d38ory
@r_cpp
When avoid metaprogrammation ?
Hi there,
I am still a junior software developer, and I quite often encounter the same question: when/why avoid metaprogrammation ?
Do you have examples where metaprogrammation became absolute bloated and the code unmaintenable ?
This language feature is really powerful and I currently use it at work.
I need to implement a quite similar behavior for 20 different data type (receive data, store it, and send it when needed).
Since this is always the same behavior, I suggested to use metaprogrammation (for some reason, basic OOP is not sufficient). I like the idea of one template class, and avoid writing 20 classes and finally 40 .h/.cpp files.
My project is largely written in c++03, despite we compile it in c++11 and some components in c++17, without using 1/10 of c++ features (large part of the team comes from embedded C).
Thanks for your always interesting answers!
https://redd.it/1d2taq1
@r_cpp
How To Develop Special AI Activation Functions In C++?
https://learncplusplus.org/how-to-develop-special-ai-activation-functions-in-c
https://redd.it/1d2hq6j
@r_cpp
Rapid Development with Runtime Compiled C++ Talk
https://www.enkisoftware.com/devlogpost-20240528-1-Rapid-Development-with-Runtime-Compiled-C++-Talk
https://redd.it/1d2iye9
@r_cpp
[P2996] Static perfect hashing (enum_to_string/string_to_enum)
Just some fun with applying static perfect hashing - https://en.wikipedia.org/wiki/Perfect_hash_function and reflection with run-time performance in mind.
- Static reflection - https://wg21.link/P2996
- Static perfect hashing library - https://github.com/boost-ext/mph
Example
enum class fib {
F0 = 0, F1 = 1, F2 = 1, F3 = 2,
F4 = 3, F5 = 5, F6 = 8, F7 = 13,
F8 = 21, F9 = 34, F10 = 55, F11 = 89,
F12 = 144, F13 = 233, F14 = 377,
F15 = 610, F16 = 987,
};
> enum_to_string
template<class E> requires std::is_enum_v<E>
inline constexpr auto enumerators = []<auto... Ns>(std::index_sequence<Ns...>) {
return std::array{
std::pair{
[:std::meta::enumerators_of(^E)[Ns]:],
std::meta::name_of(std::meta::enumerators_of(^E)[Ns]).data() // null terminated
}...
};
}(std::make_index_sequence<std::size(std::meta::enumerators_of(^E))>{});
template<class E> requires std::is_enum_v<E>
[[nodiscard]] constexpr auto enum_to_string(const E value) {
return mph::lookup<enumerators<E>>(value);
}
template<class E, auto probability = 100u> requires std::is_scoped_enum_v<E>
[[nodiscard]] constexpr auto unsafe$enum_to_string(const E value) {
return mph::lookup<enumerators<E>>.template operator()<probability>(value);
}
---
enum_to_string(fib):
movl %edi, %ecx
andl $1023, %ecx
shll $4, %ecx
leaq mph::v3_0_0::lookup<enumerators<fib>, 1u, 0u>(%rip), %rdx
xorl %eax, %eax
cmpl %edi, (%rcx,%rdx)
cmoveq 8(%rcx,%rdx), %rax
retq
unsafe$enum_to_string(fib):
andl $1023, %edi
shll $4, %edi
leaq mph::v3_0_0::lookup<enumerators<fib>, 1u, 0u>(%rip), %rax
movq 8(%rdi,%rax), %rax
retq
mph::v3_0_0::lookup<enumerators<fib>, 1u, 0u>:
... (size = 2^popcount(mask))
> Full example: https://godbolt.org/z/oxdY7K8nd
---
> string_to_enum
template<class E> requires std::is_enum_v<E>
inline constexpr auto enumerators = []<auto... Ns>(std::index_sequence<Ns...>) {
return std::array{
std::pair{
std::meta::name_of(std::meta::enumerators_of(^E)[Ns]),
[:std::meta::enumerators_of(^E)[Ns]:],
}...
};
}(std::make_index_sequence<std::size(std::meta::enumerators_of(^E))>{});
template<class E> requires std::is_enum_v<E>
[[nodiscard]] constexpr auto string_to_enum(std::string_view str) {
return mph::lookup<enumerators<E>>(str);
}
template<class E, auto probability = 100u> requires std::is_scoped_enum_v<E>
[[nodiscard]] constexpr auto unsafe$string_to_enum(std::string_view str) {
return mph::lookup<enumerators<E>>.template operator()<probability>(str);
}
---
string_to_enum(std::string_view):
shll $3, %esi
bzhil %esi, (%rdi), %ecx
movl $1511168, %eax
pextl %eax, %ecx, %edx
leaq mph::v3_0_0::lookup<enumerators<fib>, 1u, 0u>(%rip), %rsi
xorl %eax, %eax
cmpl (%rsi,%rdx,8), %ecx
cmovel 4(%rsi,%rdx,8), %eax
retq
unsafe$string_to_enum(std::string_view):
shll $3, %esi
bzhil %esi, (%rdi), %eax # using SWAR - might be unsafe without MPH_PAGE_SIZE
movl $1511168, %ecx
pextl %ecx, %eax, %eax
leaq mph::v3_0_0::lookup<enumerators<fib>, 1u, 0u>(%rip), %rcx
movl 4(%rcx,%rax,8), %eax
retq
mph::v3_0_0::lookup<enumerators<fib>, 1u, 0u>:
... (size = 2^popcount(mask))
> Full example: https://godbolt.org/z/4KcxEW9qP
Notes
- `unsafe$...` - assumes only valid inputs - meaning that given input can be found in the predefined set - therefore unsafe as it may cause a collision.
Alternatives
- SIMD (if available) - https://en.wikipedia.org/wiki/Single_instruction,_multiple_data
- https://www.gnu.org/software/gperf (only string to enum)
-
Short video on optimizing software performance
https://www.youtube.com/shorts/Z2-PCLAoMyw?feature=share
https://redd.it/1d2enkb
@r_cpp
SFTP, with private key as a buffer in curl
I want to connect to remote server using sftp and libcurl only providing private key as a buffer. I have implemented successful file transfer application by providing key file path. But ai need to pass private key as a string because of the security reasons. Making a temporary file is also not a solution.
My question is, is this possible? If so how can I do this?
If it is not possible, what are the best alternatives with C+++.
https://redd.it/1d2cmhs
@r_cpp
MSVC 14.3 slower generated executable code than MSVC 9.0
I have migrated a project that uses MSVC 9.0 in 32 bits (Visual Studio 2008) to MSVC 14.3 (Visual Studio 2022).
The old version is in 32 bits, and the new one is in 64 bits.
The new version takes 70% longer in a specific part where a very intensive calculation is performed.
Although the old program uses an old version of OpenCV and the new one uses a new version, the part in question operates on the image using only trivial calculations and also STL, without any calls to library functionality.
We are, of course, talking about the release version with the same optimizations enabled.
Does anyone have any comments to share?
https://redd.it/1d29g74
@r_cpp
What are some good C++ libs for part-of-speech tagging in English?
https://redd.it/1d20em0
@r_cpp
Function Composition and the Pipe Operator in C++23 – With std::expected
https://www.cppstories.com/2024/pipe-operator/
https://redd.it/1d1utzh
@r_cpp
