GCC 5.4.0于2016年6月发布；在采用C ++ 17标准之前的一年多。它及其libstdc ++版本对C ++ 17的支持非常有限。您可以在此处中看到GCC添加C ++ 17语言功能的时间，以及libstdc ++添加时的时间C ++ 17标准库功能此处。

GCC 5.4.0 was released in June of 2016; over a year before the C++17 standard was adopted. It and its version of libstdc++ have very limited C++17 support. You can see when GCC added C++17 language features here and when libstdc++ added C++17 standard library features here.

在GCC 5.4发布时，文件系统库尚未在 std :: filesystem 中实现>名称空间。它以及任何其他< experimental /...& gt;该版本中包含的标头位于 std :: experimental 命名空间中。

At the time of GCC 5.4's release, the filesystem library was not yet implemented in the std::filesystem namespace. It, along with any other <experimental/...> headers that are included in that version, are in the std::experimental namespace.