解决.net5调用DLL用StringBuilder接收时乱码的问题

比如如下调用

 [DllImport("CDLLDemo.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
 private static extern IntPtr ParseBaliseMsg5([MarshalAs(UnmanagedType.LPStr)]StringBuilder msg, string rmsg, [MarshalAs(UnmanagedType.LPStr)]StringBuilder t);
改成

[DllImport("CDLLDemo.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
 private static extern IntPtr ParseBaliseMsg5([MarshalAs(UnmanagedType.LPStr)]StringBuilder msg, string rmsg, ref IntPtr t);
调用

  IntPtr sb5= Marshal.StringToHGlobalAnsi("str");

  var r5 = ParseBaliseMsg5(sb5E_para, "", ref sb5);
            var str= Marshal.PtrToStringAnsi(r5);
这样获取出来的str就不再是乱码了