郁闷，简章的问题改错。

[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
public static extern int GetShortPathName(
   [MarshalAs(UnmanagedType.LPTStr)]
   string path,
   [MarshalAs(UnmanagedType.LPTStr)]
   StringBuilder shortPath,
   int shortPathLength);
StringBuilder shortPath = new StringBuilder(80);
int result = GetShortPathName(
@"d:\test.jpg", shortPath, shortPath.Capacity);
string s = shortPath.ToString();