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本期文章由 不语 HNY {} 赞助
周末有点忙，内容不多，这周争取双更
话说看到了别人的知识星球真有一种这也能卖钱的感觉
c 知识普及还是很远，无论深度还是广度，优质内容还是太少了，这种稍微懂点就敢开知识星球开课了
资讯
标准委员会动态/ide/编译器信息放在这里
编译器信息最新动态推荐关注hellogcc公众号 本周更新 2024-02-28 第243期
文章
浅谈侵入式结构的应用 https://zhuanlan.zhihu.com/p/679066486
总结的的非常好
virtual-function-templates-with-stateful-metaprogramming-in-c -20 virtual-function-templates-with-stateful-metaprogramming-in-c -20
In C /WinRT, you shouldn’t destroy an object while you’re co_awaiting it https://devblogs.microsoft.com/oldnewthing/20240307-00/?p=109490
co_wait对象如果被析构，可能有bug
代码语言：javascript复制struct MyThing : winrt::implements<MyThing, winrt::IInspectable>
{
winrt::IAsyncAction m_pendingAction{ nullptr };
winrt::IAsyncAction DoSomethingAsync() {
auto lifetime = get_strong();
m_pendingAction = LongOperationAsync();
co_await m_pendingAction;
PostProcessing();
}
void Cancel() {
if (m_pendingAction) {
m_pendingAction.Cancel();
m_pendingAction = nullptr;
}
}
};这段代码， 如果DoSomethingAsync的时候另一个线程Cancel了，pendingAction被析构了，co_await就会挂
解决方案，co_await副本，复制一份或者decay_copy auto{}
这种指针问题和co_await关系不大，但是容易忽略，普通函数也可以触发，比如异步调用lambda，然后lambda里reset指针，这种场景，可能需要copy这个对象
Borrow Checker, Lifetimes and Destructor Arguments in C Avanced compile-time validation with stateful https://a10nw01f.github.io/post/advanced_compile_time_validation/metaprogramming
看得我眼睛疼 在线演示 https://godbolt.org/z/71qs619Ge
LLVM's 'RFC: C Buffer Hardening' at Google https://bughunters.google.com/blog/6368559657254912/llvm-s-rfc-c-buffer-hardening-at-google
安全加固 c buffer的 google内部测试加固完性能衰退也就%1 希望llvm合了
RAII all the things? https://biowpn.github.io/bioweapon/2024/03/05/raii-all-the-things.html
用unique_ptr来搞，以前讲过类似的。直接贴代码
代码语言：javascript复制struct fcloser {
void operator()(std::FILE* fp) const noexcept {
std::fclose(fp);
}
};
using file_ptr = std::unique_ptr<std::FILE, fcloser>;
struct mem_unmapper {
size_t length{};
void operator()(void* addr) const noexcept {
::munmap(addr, length);
}
};
using mapped_mem_ptr = std::unique_ptr<void, mem_unmapper>;
[[nodiscard]] inline mapped_mem_ptr make_mapped_mem(void* addr, size_t length, int prot, int flags, int fd, off_t offset) {
void* p = ::mmap(addr, length, prot, flags, fd, offset);
if (p == MAP_FAILED) { // MAP_FAILED is not NULL
return nullptr;
}
return {p, mem_unmapper{length}}; // unique_ptr owns a deleter, which remembers the length
}
// Intentionally non-RAII
class file_descriptor {
int fd_{-1};
public:
file_descriptor(int fd = -1): fd_(fd) {}
file_descriptor(nullptr_t) {}
operator int() const { return fd_; }
explicit operator bool() const { return fd_ != -1; }
friend bool operator==(file_descriptor, file_descriptor) = default; // Since C 20
};
struct fd_closer {
using pointer = file_descriptor; // IMPORTANT
void operator()(pointer fd) const noexcept {
::close(int(fd));
}
};
//using unique_fd = std::unique_ptr<int, fd_closer>; // Ok
using unique_fd = std::unique_ptr<file_descriptor, fd_closer>; // Ok
//using unique_fd = std::unique_ptr<void, fd_closer>; // Ok其他场景自己拼一个defer或者scope_exit
How do I make an expression non-movable? What’s the opposite of std::move? https://devblogs.microsoft.com/oldnewthing/20240306-00/?p=109481
如何实现强制不move？
代码语言：javascript复制template<typename T>
std::remove_reference_t<T> const& no_move(T&& t)
{
return t;
}
std::vector<int> v = no_move(make_vector());Python3.13的JIT是如何实现的 https://zhuanlan.zhihu.com/p/682997904
这个也有点意思
不用指针实现pimpl https://github.com/friendlyanon/pimpl-but-the-p-is-silent
代码很短
代码语言：javascript复制class impl
{
public:
impl();
~impl();
int add(int x) const;
private:
alignas(private_align) unsigned char buffer[private_size];
};
class impl_private
{
public:
explicit impl_private(int y);
int add(int x) const;
private:
int _y;
};
template<typename T>
using impl_t = std::conditional_t<std::is_const_v<std::remove_pointer_t<T>>,
impl_private const,
impl_private>*;
#define IMPL std::launder(reinterpret_cast<impl_t<decltype(this)>>(buffer))
impl::impl()
{
(void)new (buffer) impl_private(1);
}
impl::~impl()
{
IMPL->~impl_private();
}
int impl::add(int x) const
{
return IMPL->add(x);
}核心是用buffer存实现类，然后硬转，看一乐
