?嵌套类 ?nested
int x,y; // 全局变量
class enclose // 外围类
{
public:
struct inner // 嵌套类
{
void f(int i)
{
x = i; // 错误：不能不带实例地写入非静态的 enclose::x
int a = sizeof x; // C++11 前错误，C++11 中 OK：sizeof 的操作数不求值，
// 可以这样使用非静态的 enclose::x 。
s = i; // OK：可以赋值给静态 enclose::s
::x = i; // OK：可以赋值给全局 x
y = i; // OK：可以赋值给全局 y
}
void g(enclose* p, int i)
{
p->x = i; // OK：赋值给 enclose::x
}
};
private:
int x;
static int s;
};
?bind
// （ _1 与 _2 来自 std::placeholders ，并表示将来会传递给 f1 的参数）
auto f1 = std::bind(f, _2, 42, _1, std::cref(n), n);
?lambda ?λ
int& (*fpi)(int*) = [](int* a) -> int& { return *a; };
?继承 ?构造函数
using Base::Base;
浏览器中设定cpp帮助文档 ?manpage
- Chrome-设置-搜索引擎-管理搜索引擎和网站搜素-网站搜索-新增
- Edge-设置-搜:地址栏和搜索-管理搜索引擎-添加
cc
cc
https://zh.cppreference.com/mwiki/index.php?title=Special:%E6%90%9C%E7%B4%A2&search=%s
vscode c/cpp format settings
- F1->Preferences: Open User Settings(json)
- Ctrl+,->search formatting->C/C++ /Formatting->C_Cpp:Clang_format_style->{ BasedOnStyle: WebKit, IndentWidth: 2, TabWidth: 2}
- Editor:Format On Paste
vscode Keyboard Shortcuts
File->Preferences->Keyboard Shortcuts->cursorLineEnd->Ctrl+;
log
- 同步日志:实时性好,便于记录异常崩溃日志;但写io阻塞当前业务
- 异步日志:业务线程生成日志信息,打印线程消费;
并发实战
基于atomic_flag的自旋锁
class spinlock_mutex
{
std::atomic_flag flag;
public:
spinlock_mutex():
flag(ATOMIC_FLAG_INIT)
{}
void lock()
{
while(flag.test_and_set(std::memory_order_acquire));
}
void unlock()
{
flag.clear(std::memory_order_release);
}
};
可上锁和等待的线程安全队列
template<typename T>
class threadsafe_queue
{
private:
struct node
{
std::shared_ptr<T> data;
std::unique_ptr<node> next;
};
std::mutex head_mutex;
std::unique_ptr<node> head;
std::mutex tail_mutex;
node* tail;
std::condition_variable data_cond;
public:
threadsafe_queue():
head(new node),tail(head.get())
{}
threadsafe_queue(const threadsafe_queue& other)=delete;
threadsafe_queue& operator=(const threadsafe_queue& other)=delete;
std::shared_ptr<T> try_pop();
bool try_pop(T& value);
std::shared_ptr<T> wait_and_pop();
void wait_and_pop(T& value);
void push(T new_value);
bool empty();
};
template<typename T>
void threadsafe_queue<T>::push(T new_value)
{
std::shared_ptr<T> new_data(
std::make_shared<T>(std::move(new_value)));
std::unique_ptr<node> p(new node);
{
std::lock_guard<std::mutex> tail_lock(tail_mutex);
tail->data=new_data;
node* const new_tail=p.get();
tail->next=std::move(p);
tail=new_tail;
}
data_cond.notify_one();
}
template<typename T>
class threadsafe_queue
{
private:
node* get_tail()
{
std::lock_guard<std::mutex> tail_lock(tail_mutex);
return tail;
}
std::unique_ptr<node> pop_head() // 1
{
std::unique_ptr<node> old_head=std::move(head);
head=std::move(old_head->next);
return old_head;
}
std::unique_lock<std::mutex> wait_for_data() // 2
{
std::unique_lock<std::mutex> head_lock(head_mutex);
data_cond.wait(head_lock,[&]{return head.get()!=get_tail();});
return std::move(head_lock); // 3
}
std::unique_ptr<node> wait_pop_head()
{
std::unique_lock<std::mutex> head_lock(wait_for_data()); // 4
return pop_head();
}
std::unique_ptr<node> wait_pop_head(T& value)
{
std::unique_lock<std::mutex> head_lock(wait_for_data()); // 5
value=std::move(*head->data);
return pop_head();
}
public:
std::shared_ptr<T> wait_and_pop()
{
std::unique_ptr<node> const old_head=wait_pop_head();
return old_head->data;
}
void wait_and_pop(T& value)
{
std::unique_ptr<node> const old_head=wait_pop_head(value);
}
};
template<typename T>
class threadsafe_queue
{
private:
std::unique_ptr<node> try_pop_head()
{
std::lock_guard<std::mutex> head_lock(head_mutex);
if(head.get()==get_tail())
{
return std::unique_ptr<node>();
}
return pop_head();
}
std::unique_ptr<node> try_pop_head(T& value)
{
std::lock_guard<std::mutex> head_lock(head_mutex);
if(head.get()==get_tail())
{
return std::unique_ptr<node>();
}
value=std::move(*head->data);
return pop_head();
}
public:
std::shared_ptr<T> try_pop()
{
std::unique_ptr<node> old_head=try_pop_head();
return old_head?old_head->data:std::shared_ptr<T>();
}
bool try_pop(T& value)
{
std::unique_ptr<node> const old_head=try_pop_head(value);
return old_head;
}
bool empty()
{
std::lock_guard<std::mutex> head_lock(head_mutex);
return (head.get()==get_tail());
}
};