Function find_root_directory_start

src/path.cpp:1022–1078

Returns: starting position of root directory or size if not found

// Returns: starting position of root directory or size if not found
size_type find_root_directory_start(const value_type* path, size_type size, size_type& root_name_size)
{
    root_name_size = 0;
    if (size == 0)
        return 0;

    bool parsing_root_name = false;
    size_type pos = 0;

    // case "//", possibly followed by more characters
    if (fs::detail::is_directory_separator(path[0]))
    {
        if (size >= 2 && fs::detail::is_directory_separator(path[1]))
        {
            if (size == 2)
            {
                // The whole path is just a pair of separators
                root_name_size = 2;
                return 2;
            }
#ifdef BOOST_FILESYSTEM_WINDOWS_API
            // https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file
            // cases "\\?\" and "\\.\"
            else if (size >= 4 && (path[2] == questionmark || path[2] == fs::path::dot) && fs::detail::is_directory_separator(path[3]))
            {
                parsing_root_name = true;
                pos += 4;
            }
#endif
            else if (fs::detail::is_directory_separator(path[2]))
            {
                // The path starts with three directory separators, which is interpreted as a root directory followed by redundant separators
                return 0;
            }
            else
            {
                // case "//net {/}"
                parsing_root_name = true;
                pos += 2;
                goto find_next_separator;
            }
        }
#ifdef BOOST_FILESYSTEM_WINDOWS_API
        // https://stackoverflow.com/questions/23041983/path-prefixes-and
        // case "\??\" (NT path prefix)
        else if (size >= 4 && path[1] == questionmark && path[2] == questionmark && fs::detail::is_directory_separator(path[3]))
        {
            parsing_root_name = true;
            pos += 4;
        }
#endif
        else
        {
            // The path starts with a separator, possibly followed by a non-separator character
            return 0;
        }
    }