Bug 99430 - std::filesystem::path: UNC device paths with \\?\… not supported properly
Summary: std::filesystem::path: UNC device paths with \\?\… not supported properly
Status: UNCONFIRMED
Alias: None
Product: gcc
Classification: Unclassified
Component: libstdc++ (show other bugs)
Version: 10.2.0
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2021-03-06 16:11 UTC by Moritz Bunkus
Modified: 2021-04-08 09:42 UTC (History)
1 user (show)

See Also:
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Target:
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Known to work:
Known to fail:
Last reconfirmed:


Attachments
test case highlighting the issue (352 bytes, text/x-csrc)
2021-03-06 16:11 UTC, Moritz Bunkus
Details

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Description Moritz Bunkus 2021-03-06 16:11:51 UTC
Created attachment 50317 [details]
test case highlighting the issue

Paths such as \\?\C:\WINDOWS or \\?\UNC\LOCALHOST\c$\WINDOWS don't work properly with std::filesystem::path (e.g. exists() & is_directory() return false).

According to Microsoft's documentation those are valid.[1]

The corresponding variants starting with \\.\ seem to fare better (safe for the root name & absolute issues, but I've filed 99333 for that already).

boost::filesystem works fine with all of these paths.

The attached sample program outputs the following, showing how Boost's & std's implementation differ:

-----------------------------------------
std::filesystem::path for \\?\C:\WINDOWS
  is_aboslute 0
  has_root_path 1
  has_root_name 0
  exists 0
  is_directory 0
boost::filesystem::path for \\?\C:\WINDOWS
  is_aboslute 1
  has_root_path 1
  has_root_name 1
  exists 1
  is_directory 1
std::filesystem::path for \\?\UNC\localhost\c$\WINDOWS
  is_aboslute 0
  has_root_path 1
  has_root_name 0
  exists 0
  is_directory 0
boost::filesystem::path for \\?\UNC\localhost\c$\WINDOWS
  is_aboslute 1
  has_root_path 1
  has_root_name 1
  exists 1
  is_directory 1
std::filesystem::path for \\.\C:\WINDOWS
  is_aboslute 0
  has_root_path 1
  has_root_name 0
  exists 1
  is_directory 1
boost::filesystem::path for \\.\C:\WINDOWS
  is_aboslute 1
  has_root_path 1
  has_root_name 1
  exists 1
  is_directory 1
std::filesystem::path for \\.\UNC\localhost\c$\WINDOWS
  is_aboslute 0
  has_root_path 1
  has_root_name 0
  exists 1
  is_directory 1
boost::filesystem::path for \\.\UNC\localhost\c$\WINDOWS
  is_aboslute 1
  has_root_path 1
  has_root_name 1
  exists 1
  is_directory 1
-----------------------------------------

gcc mingw 10.2.0 from MXE (cross-compiling from Linux to Windows), Boost 1.74.0

[1] https://docs.microsoft.com/en-us/dotnet/standard/io/file-path-formats
Comment 1 Jonathan Wakely 2021-03-07 16:33:28 UTC
They're simply not supported at all.