[boost] [Filesystem] Querying a card reader can throw on Windows

From: Angus Leeming (angus.leeming_at_[hidden])
Date: 2006-03-31 10:21:40

Hi, Beman.

If I understand correctly, the idiom to check whether a directory exists
using Boost.Filesystem is

    if (fs::exists(path) && fs::is_directory(path))

Under normal conditions the code above shouldn't throw, right?

One of our users reports that this code does, however, throw when it is
used on Windows to query a card reader that has a drive letter J: assigned
to it.

Below is a diagnostic program that attempts to query a
nonexistent "J:\foo". Executing it, our user finds:

   1. If no drive is associated with J:
      then the program outputs nothing.

   2. If an empty drive is associated with J:

        Exception caught:
        boost::filesystem::is_directory: "J:\foo":
            The device is not ready.  
        Assertion failed: false file ekkehart.cpp, line 40

   3. If the drive contains a disk the program
      outputs nothing.

He goes on to say:

   The problem described disappears if I do one
   of the following:

   1. Reassign another letter to the smart cars slot
      (such that J: is not assigned to any drive)

   2. Reassign J: to a used slot (in my case the compact
      flash slot) and insert a card.

   3. Remove the card reader.

   Conclusion: You should have either no drive assigned
   to J: or a drive with an inserted medium.

This is with the current release of Boost, 1.33.1.

Is this a known problem (is there a workaround) or have we stumbled upon a
bug?

Kind regards,
Angus

/*
   Compiled with
   g++ -fno-exceptions -Iboost -o ekkehart ekkehart.cpp \
      -Lbuild/boost/libs/filesystem/src/.libs -lboost_filesystem
 */

#include <boost/filesystem/operations.hpp>
#include <boost/filesystem/path.hpp>
#include <cassert>
#include <cstdlib>
#include <exception>
#include <iostream>

namespace fs = boost::filesystem;

int main()
{
   fs::path const path("J:/foo", fs::no_check);
   if (fs::exists(path) && fs::is_directory(path))
     std::cout << path.native_directory_string()
               << "is a directory" << std::endl;
   return 0;
}

namespace boost {

void throw_exception(std::exception const & e)
{
        std::cerr << "Exception caught:\n"
                  << e.what() << std::endl;
        assert(false);
}

void assertion_failed(char const * expr, char const * function,
                      char const * file, long line)
{
        std::cerr << "Assertion triggered in " << function
                  << " by failing check \"" << expr << "\""
                  << " in file " << file << ":" << line << std::endl;
        ::abort();
}

} // namespace boost