Why does the following path initialization throw this?

"boost::filesystem::path: invalid name "c:" in path: "c:/dev/Sandbox/file_system/
textfile1.txt"

How do you set paths that should work on windows and linux without avoiding this issue? Since linux doesn't have drive like C: D: and etc?

try
{
// Is this not an appropriate method to initialize path objects?
    path text_file(current_path().string() + "/textfile1.txt");

     if (exists(text_file))
     { cout << file_size(text_file) << endl; }
}
catch (const filesystem_error& e)
{
    cout << e.what() << endl;
}

I am running this under windows.

Thanks,
Graham