Method decrement_v4

src/path.cpp:1339–1397

}

BOOST_FILESYSTEM_DECL void path_algorithms::decrement_v4(path_detail::path_iterator& it)
{
    const size_type size = it.m_path_ptr->m_pathname.size();
    BOOST_ASSERT_MSG(it.m_pos > 0, "path::iterator decrement past begin()");
    BOOST_ASSERT_MSG(it.m_pos <= size, "path::iterator decrement after the referenced path was modified");

    size_type root_name_size = 0;
    size_type root_dir_pos = find_root_directory_start(it.m_path_ptr->m_pathname.c_str(), size, root_name_size);

    if (root_dir_pos < size && it.m_pos == root_dir_pos)
    {
        // Was pointing at root directory, decrement to root name
    set_to_root_name:
        it.m_pos = 0u;
        const path::value_type* p = it.m_path_ptr->m_pathname.c_str();
        it.m_element.m_pathname.assign(p, p + root_name_size);
        return;
    }

    // if at end and there was a trailing '/', return ""
    if (it.m_pos == size &&
        size > 1 &&
        detail::is_directory_separator(it.m_path_ptr->m_pathname[it.m_pos - 1]) &&
        !is_root_separator(it.m_path_ptr->m_pathname, root_dir_pos, it.m_pos - 1))
    {
        --it.m_pos;
        it.m_element.m_pathname.clear();
        return;
    }

    // skip separators unless root directory
    size_type end_pos = it.m_pos;
    while (end_pos > root_name_size)
    {
        --end_pos;

        if (end_pos == root_dir_pos)
        {
            // Decremented to the root directory
            it.m_pos = end_pos;
            it.m_element.m_pathname = path::separator; // generic format; see docs
            return;
        }

        if (!detail::is_directory_separator(it.m_path_ptr->m_pathname[end_pos]))
        {
            ++end_pos;
            break;
        }
    }

    if (end_pos <= root_name_size)
        goto set_to_root_name;

    size_type filename_size = find_filename_size(it.m_path_ptr->m_pathname, root_name_size, end_pos);
    it.m_pos = end_pos - filename_size;
    const path::value_type* p = it.m_path_ptr->m_pathname.c_str();
    it.m_element.m_pathname.assign(p + it.m_pos, p + end_pos);