Re: [boost] recursive_directory_iterator assertion failure

From: eric ehlers (eric.ehlers_at_[hidden])
Date: 2007-09-04 07:58:31

Hello,

On 9/4/07, eric ehlers <eric.ehlers_at_[hidden]> wrote:
> Hello,
>
> Using boost version 1.34.1 I get an assertion failure when comparing
> recursive_directory_iterator to the end iterator if the corresponding
> path comprises an empty directory.
>
>         // a directory that is not empty - runs OK
>         //boost::filesystem::path boostPath("C:\\test_notempty");
>         // a directory that is empty - crashes
>         boost::filesystem::path boostPath("C:\\test_empty");
>
>         if (boost::filesystem::is_directory(boostPath)) {
>             boost::filesystem::recursive_directory_iterator end_itr;
>             for (boost::filesystem::recursive_directory_iterator
> itr(boostPath); itr != end_itr; ++itr) {
>                 std::cout << itr->path().string() << std::endl;
>             }
>         }
>
> Assertion failed: m_imp.get() && "attempt to dereference end iterator", file c:\
> program files\boost\boost_1_34_1\boost\filesystem\operations.hpp, line 849
>
> This issue has been reported before:
>
> http://lists.boost.org/Archives/boost/2006/10/111230.php
>
> What's the workaround?  I can't seem to find any way to inspect the
> path or its iterator to distinguish an empty directory from a nonempty
> one without crashing the program.

On further analysis it seems that, with an empty directory, comparing
a recursive iterator to the end iterator returns false, while
performing the same comparison with a normal iterator returns true.

    boost::filesystem::path p1("C:\\test_notempty");
    boost::filesystem::path p2("C:\\test_empty");

    // nonempty directory, normal iterator - outputs 0
    cout << (boost::filesystem::directory_iterator(p1)
        == boost::filesystem::directory_iterator()) << endl;
    // empty directory, normal iterator - outputs 1
    cout << (boost::filesystem::directory_iterator(p2)
        == boost::filesystem::directory_iterator()) << endl;
    // nonempty directory, recursive iterator - outputs 0
    cout << (boost::filesystem::recursive_directory_iterator(p1)
        == boost::filesystem::recursive_directory_iterator()) << endl;
    // empty directory, recursive iterator - outputs 0
    cout << (boost::filesystem::recursive_directory_iterator(p2)
        == boost::filesystem::recursive_directory_iterator()) << endl;

So I guess that before using a recursive iterator to iterate over a
directory you must first use a normal iterator to test whether the
directory is empty.

Regards,
Eric