UU编码原理及应用

fprintf (stderr, "uuencode: Couldn't open output file %s\n", argv [2]);
exit (1); }
/* Write the 'begin' line, giving it a mode of 0600 */
fprintf (outfile, "begin 600 %s\n", argv [1]);
In addition, the start of the encoding is marked by the line "start <mode> <filename>", where
<mode> consists of 3 octal digits which are the Unix mode of the file, and
Then convert these bytes to printable characters by adding 0x20 (32). EXCEPTION: if you end up with a zero byte it should be converted to 0x60 (back-quote '`') rather than 0x20 (space ' ').
Lines in the encoded file are always a multiple of 4 + 1 characters long; this sometimes means that 1 or 2 bytes are thrown away at the end of the decoding.
a7a6a5a4a3a2a1a0 b7b6b5b4b3b2b1b0 c7c6c5c4c3c2c1c0
and convert them into 4 bytes with values in the range 0-63 as follows:
0 0 a7a6a5a4a3a2 0 0 a1a0b7b6b5b4 0 0 b3b2b1b0c7c6 0 0 c5c4c3c2c1c0
00000101 00000000 00111110 00101000
Note that the zero byte has been translated to 0x60 instead of 0x20. The body of a uuencoded file therefore only contains the characters 0x21 '!' to 0x60 '`', which are all printable and capable of being transmitted by email. (Note: this of course means that uuencoded files are slightly more than 33% longer than the originals. uuencoding text-only files is redundant and a silly thing to do. Standard and sensible practice is to compress the files first using a standard compression utility and then to uuencode them).
(Note: I can't see any reason why lines shouldn't be an arbitrary length, and don't know whether the proper definition disallows this. I've never seen a uuencoded file where any line apart from the last one wasn't 'M' followed by 60 characters, though)
if (argc != 3) {
fprintf (stderr, "Syntax: uuencode <infile> <outfile>\n"); exit (1); }
/* Try and open the input file (binary) */
infile = fopen (argv [1], "rb"); if (infile == NULL) {
Date: Wed, 09 Apr 1997 13:04:11 +0100 From: jim <j.cameron@> To: webmaster@
Uuencode.txt
===== UUENCODE ======
uuencode is a utility designed to enable arbitrary binary files to be transmitted using text-only media such as email. It does this by encoding the files in such a way that the encoded file contains only printable characters.
do {
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/* Read a line from input file */
Uuencode.txt
linelen = fread (inbuf, 1, MAX_LINELEN, infile);
/* Write the line length byte */
fputc (ENCODE_BYTE (linelen), outfile);
(IMPORTANT Note: this file is the result of an afternoon's hacking by myself. I make no guarantees as to its completeness and accuracy. I have coded my own uuencode and uudecode programs which haven't let me down yet)
typedef unsigned char BYTE;
int main (int argc, char *argv []) {
FILE *infile = NULL; FILE *outfile = NULL; int linelen; int linecnt; BYTE inbuf [MAX_LINELEN]; BYTE *inbytep; chancode.txt To decode, simply perform the inverse of the encoding algorithm.
===== SAMPLE CODE =====
I include here the C source code to a small uuencode and uudecode utility I coded myself. It isn't very sophisticated and probably not very complete, but it does its job, and is very useful for my PC where I don't have access to the standard Unix stuff. It took me about half an hour to write, and another hour or so to iron out the obvious bugs. It works quite happily under DOS (uuencoding needs practically no internal storage). It isn't a great masterpiece of software design and coding, but might be worth a look. Feel free to do whatever you want to it, up to and including throwing it in the bin.
/* Encode the line */
for (linecnt = linelen, inbytep = inbuf; linecnt > 0; linecnt -= 3, inbytep += 3)
So if you read 3 bytes from the file as follows: 14 0F A8 (hex) i.e.
00010100 00001111 10101000
your 4 bytes output should be 25 60 5E 48 ("%`^H"). The intermediate 4 bytes in this case were
The uuencode algorithm hinges around a 3-byte-to-4-byte (8-bit to 6-bit data) encoding to convert all data to printable characters. To perform this encoding read in 3 bytes from the file to be encoded whose binary representation is
<filename> is the original filename of the file encoded.