它将返回。广州，而是从MSDN（解释的FileSystemInfo.Extension物业）目前尚不清楚为什么：

It will return .gz, but the explanation from MSDN (FileSystemInfo.Extension Property) isn't clear why:

的的扩展属性返回FileSystemInfo扩展，包括句例如，对于一个文件c（）：\NewFile.txt，此属性返回.TXT

于是我抬起头，反射器扩展属性代码：

So I looked up the code of the Extension property with reflector:

public string Extension
{
    get
    {
        int length = this.FullPath.Length;
        int startIndex = length;
        while (--startIndex >= 0)
        {
            char ch = this.FullPath[startIndex];
            if (ch == '.')
            {
                return this.FullPath.Substring(startIndex, length - startIndex);
            }
            if (((ch == Path.DirectorySeparatorChar) || (ch == Path.AltDirectorySeparatorChar)) || (ch == Path.VolumeSeparatorChar))
            {
                break;
            }
        }
        return string.Empty;
    }
}

这是从文件路径的末尾，直到检查每一个字符它找到一个点，那么子从点到文件路径的末尾返回。

It's check every char from the end of the filepath till it finds a dot, then a substring is returned from the dot to the end of the filepath.