An example of an XDR data description

Here is a short XDR data description of a thing called a file, which might be used to transfer files from one machine to another:

   const MAXUSERNAME = 32;     /* max length of a user name */
   const MAXFILELEN = 65535;   /* max length of a file */
   const MAXNAMELEN = 255;     /* max length of a file name */
   

   /* Types of files: */
   

   enum filekind {
   	TEXT = 0,       /* ascii data */
   	DATA = 1,       /* raw data   */
   	EXEC = 2        /* executable */
   };
   

   /* File information, per kind of file: */
   

   union filetype switch (filekind kind) {
   	case TEXT:
   		void;                           /* no extra information */
   	case DATA:
   		string creator<MAXNAMELEN>;     /* data creator */
   	case EXEC:
   		string interpretor<MAXNAMELEN>; /* program interpretor  */
   };
   

   /* A complete file: */
   

   struct file {
   	string filename<MAXNAMELEN>; /* name of file */
   	filetype type;               /* info about file */
   	string owner<MAXUSERNAME>;   /* owner of file */
   	opaque data<MAXFILELEN>;     /* file data */
   };

Offset	Hex bytes	ASCII	Description
0	00 00 00 09	....	Length of filename = 9
4	73 69 6c 6c	sill	Filename characters
8	79 70 72 6f	ypro	... and more characters ...
12	67 00 00 00	g...	... and 3 zero-bytes of fill
16	00 00 00 02	....	Filekind is EXEC = 2
20	00 00 00 04	....	Length of interpretor = 4
24	6c 69 73 70	lisp	Interpretor characters
28	00 00 00 04	....	Length of owner = 4
32	6a 6f 68 6e	john	Owner characters
36	00 00 00 06	....	Length of file data = 6
40	28 71 75 69	(qui	File data bytes ...
44	74 29 00 00	t)..	... and 2 zero-bytes of fill