c++ - 当 C++ 中需要自动删除时，这种静态用法是否正确？

Question

code snippet来自维基百科。

void WriteToFile(const std::string& message) {
  // |mutex| is to protect access to |file| (which is shared across threads).
  static std::mutex mutex;

  // Lock |mutex| before accessing |file|.
  std::lock_guard<std::mutex> lock(mutex);

  // Try to open file.
  std::ofstream file("example.txt");
  if (!file.is_open()) {
    throw std::runtime_error("unable to open file");
  }

  // Write |message| to |file|.
  file << message << std::endl;

  // |file| will be closed first when leaving scope (regardless of exception)
  // mutex will be unlocked second (from lock destructor) when leaving scope
  // (regardless of exception).
}

此片段用于演示 RAII。当离开 WriteToFile 范围时，互斥量将被解锁。我的问题是，由于 mutex 被声明为 static，它应该存在直到整个程序退出，对吗？那么为什么在离开作用域时会调用互斥析构函数呢？我认为互斥析构函数只在主程序退出后调用一次，正如 C++ 标准所指定的那样。

有人给我解释一下吗？

Answer 1

it should exist until the whole program exit, right?

是的

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So why would the mutex destructor be called when leaving the scope?

互斥析构函数不会被调用。锁守卫析构函数将被调用，它将解锁互斥量。

来自 cppreference

When a lock_guard object is created, it attempts to take ownership ofthe mutex it is given. When control leaves the scope in which thelock_guard object was created, the lock_guard is destructed and themutex is released.

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I think the mutex destructor only be called once after the mainprogram exit

是的