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 */ };
Suppose now that there is a user named "john" who wants to store his lisp program "sillyprog" that contains just the data "(quit)". His file would be encoded as follows:
OFFSET HEX BYTES ASCII COMMENTS ------ --------- ----- -------- 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