Boost C++ 库

...世界上最受推崇和设计精良的 C++ 库项目之一。 — Herb Sutter 和 Andrei Alexandrescu，《C++ 编码规范

windows::basic_overlapped_handle::is_open - Boost C++ 函数库

windows::basic_overlapped_handle::is_open

确定句柄是否已打开。

bool is_open() const;