[原]System.IO.Path.Combine 路径合并

// System.IO.Path
/// <summary>Combines two path strings.</summary>
/// <returns>A string containing the combined paths. If one of the specified paths is a zero-length string, this method returns the other path. If <paramref name="path2" /> contains an absolute path, this method returns <paramref name="path2" />.</returns>
/// <param name="path1">The first path. </param>
/// <param name="path2">The second path. </param>
/// <exception cref="T:System.ArgumentException">
///   <paramref name="path1" /> or <paramref name="path2" /> contain one or more of the invalid characters defined in <see cref="M:System.IO.Path.GetInvalidPathChars" />. </exception>
/// <exception cref="T:System.ArgumentNullException">
///   <paramref name="path1" /> or <paramref name="path2" /> is null. </exception>
/// <filterpriority>1</filterpriority>
public static string Combine(string path1, string path2)
{
    if (path1 == null || path2 == null)
    {
        throw new ArgumentNullException((path1 == null) ? "path1" : "path2");
    }
    Path.CheckInvalidPathChars(path1);
    Path.CheckInvalidPathChars(path2);
    if (path2.Length == 0)
    {
        return path1;
    }
    if (path1.Length == 0)
    {
        return path2;
    }
    if (Path.IsPathRooted(path2))
    {
        return path2;
    }
    char c = path1[path1.Length - 1];
    // if (c != ‘\\‘ && c != ‘/‘ && c != ‘:‘)
    if (c != Path.DirectorySeparatorChar && c != Path.AltDirectorySeparatorChar && c != Path.VolumeSeparatorChar)
    {
        // return path1 + ‘\\‘ + path2;
        return path1 + Path.DirectorySeparatorChar + path2;
    }
    return path1 + path2;
}