本期文章由 HMY lhmouse赞助
资讯
标准委员会动态/ide/编译器信息放在这里
最近陆陆续续又有很多c 26 St Louis参会报告出来，这里列一下
https://mpusz.github.io/mp-units/latest/blog/2024/07/02/report-from-the-st-louis-2024-iso-c-committee-meeting/
https://quuxplusone.github.io/blog/2024/06/30/st-louis-trip-report/
https://herbsutter.com/2024/07/02/trip-report-summer-iso-c-standards-meeting-st-louis-mo-usa/
https://www.reddit.com/r/cpp/comments/1dwc7f2/202406_st_louis_iso_c_committee_trip_report/
另外上周也介绍了mick的报告
另外Ykiko也写了一个 St. Louis WG21 会议回顾
知乎原文 https://zhuanlan.zhihu.com/p/706509748
文章
Can you change state in a const function in C ? Why? How?
https://bytesandlogs.me/can-you-change-state-in-const-function-in-cpp/
const_cast
Cooperative Interruption of a Thread in C 20
https://www.modernescpp.com/index.php/cooperative-interruption-of-a-thread-in-c20/
介绍stop_token，其实就是塞了个状态回调，规范化了一下 直接看代码
代码语言：javascript复制#include <chrono>
#include <iostream>
#include <thread>
#include <vector>
usingnamespace::std::literals;
auto func =[](std::stop_token stoken){// (1)
int counter{0};
auto thread_id = std::this_thread::get_id();
std::stop_callback callBack(stoken, [&counter, thread_id] { // (2)
std::cout << "Thread id: " << thread_id
<< "; counter: " << counter << 'n';
});
while(counter <10){
std::this_thread::sleep_for(0.2s);
counter;
}
};
int main() {
std::vector<std::jthread> vecThreads(10);
for(auto& thr: vecThreads) thr = std::jthread(func);
std::this_thread::sleep_for(1s);// (3)
for(auto& thr: vecThreads) thr.request_stop();// (4)
}A 16-byte std::function implementation
https://www.reddit.com/r/cpp/comments/1dwkgue/a_16byte_stdfunction_implementation/
直接贴代码吧
代码语言：javascript复制template<typename T>
struct sfunc;
template<typename R, typename ...Args>
struct sfunc<R(Args...)> {
struct lambda_handler_result {
void* funcs[3];
};
enum class tag {
free,
copy,
call
};
lambda_handler_result (*lambda_handler)(void*, void**) {nullptr};
void* lambda {nullptr};
template<typename F>
sfunc(F f) { *this = f;}
sfunc() {}
sfunc(const sfunc& f) { *this = f; }
sfunc(sfunc&& f) { *this = f; }
sfunc& operator = (sfunc&& f) {
if(&f == this){
return *this;
}
lambda_handler = f.lambda_handler;
lambda = f.lambda;
f.lambda_handler = nullptr;
f.lambda = nullptr;
return *this;
}
void free_lambda() {
if(lambda_handler) {
auto ff {lambda_handler(lambda, nullptr).funcs[(int)tag::free]};
if(ff){
((void(*)(void*))ff)(lambda);
}
}
lambda = nullptr;
}
sfunc& operator = (const sfunc& f) {
if(&f == this) {
return *this;
}
free_lambda();
lambda_handler = f.lambda_handler;
if(f.lambda) {
auto ff {lambda_handler(lambda, nullptr).funcs[(int)tag::copy]};
if(ff) {
((void(*)(void*, void**))ff)(f.lambda, &lambda);
} else {
lambda = f.lambda;
}
}
return *this;
}
template<typename ...>
struct is_function_pointer;
template<typename T>
struct is_function_pointer<T> {
static constexpr bool value {false};
};
template<typename T, typename ...Ts>
struct is_function_pointer<T(*)(Ts...)> {
static constexpr bool value {true};
};
template<typename F>
auto operator = (F f) {
if constexpr(is_function_pointer<F>::value == true) {
free_lambda();
lambda = (void*)f;
lambda_handler = [](void* l, void**) {
return lambda_handler_result{{nullptr, nullptr, (void*) [](void* l, Args... args) {
auto& f {*(F)l};
return f(forward<Args>(args)...);
}}};
};
} else {
free_lambda();
lambda = {new F{f}};
lambda_handler = [](void* d, void** v) {
return lambda_handler_result{{(void*)[](void*d){ delete (F*)d;},
(void*)[](void*d, void** v){ *v = new F{*((F*)d)};},
(void*)[](void* l, Args... args)
{
auto& f {*(F*)l};
return f(forward<Args>(args)...);
}}};
};
}
}
inline R operator()(Args... args) {
return ((R(*)(void*, Args...))lambda_handler(nullptr, nullptr).funcs[(int)tag::call])(lambda, forward<Args>(args)...);
}
~sfunc() { free_lambda(); }
};没SSO
A Type for Overload Set
https://biowpn.github.io/bioweapon/2024/07/02/a-type-for-overload-set.html
函数没有类型，直接赋值是不可以的
代码语言：javascript复制void f(int);
void f(int, int);
// `f` is an overload set with 2 members
auto g = f;// error! cannot deduce the type of `g`
// This is because:
using FF =decltype(f);// error! overload set has not type
std::invocable<int>auto g = f;// error! cannot deduce the type of `g`
// bind invoke也不行，他们要接受对象而lambda有类型，即使这个类型看不到，那么就可以封装一层
代码语言：javascript复制#include <cassert>
#include <utility>
int g(int x) { return x 1; }
int g(int x, int y) { assert(false); }
class MyClass {
public:
int f(int x) { return x 1; }
int f(int x, int y) { assert(false); }
};
#define OVERLOAD(...) [&](auto &&... args) -> decltype(auto) {
return __VA_ARGS__(std::forward<decltype(args)>(args)...);
}
int main(int argc, char *argv[]) {
assert(OVERLOAD(g)(5) == 6);
MyClass obj;
assert(OVERLOAD(obj.f)(5) == 6);
return 0;
}godbolt https://godbolt.org/z/zrcsaG9xE
P3312就是这盘饺子 https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p3312r0.pdf
Compile-time JSON deserialization in C https://medium.com/@abdulgh/compile-time-json-deserialization-in-c-1e3d41a73628
没看懂
Beating NumPy's matrix multiplication in 150 lines of C code https://salykova.github.io/matmul-cpu
代码在这 https://github.com/salykova/matmul.c
感觉不是很靠谱，影响因素太多了
视频
C Weekly - Ep 435 - Easy GPU Programming With AdaptiveCpp (68x Faster!)
https://www.youtube.com/watch?v=ImM7f5IQOaw&ab_channel=C++WeeklyWithJasonTurner
介绍opensycl的 https://github.com/AdaptiveCpp/AdaptiveCpp
自己看吧，我不是业内，不了解
Björn Fahller: Cache friendly data functional ranges = ❤️
https://www.youtube.com/watch?v=3Rk-zSzloL4&ab_channel=SwedenCpp
https://github.com/rollbear/columnist 他这个SOA库还挺有意思的
