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To: cs551@merlot.usc.edu
Subject: Re: CS551_Final2_index files
Date: Thu, 20 Nov 2008 08:09:01 -0800
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  > *So name_index should be sorted alphabetically. How will sha1_index be
  > sorted ? Will it be in the decreasing order of ascii values of SHA1* ?

It's up to you.  You need to be a little more careful if you
store SHA1 in binary.  If you use a comma or a tab as a
delimeter between fields, it is possible that the SHA1 value
may contain this character.  So, when you read the sha1_index
file, you should read 20 bytes first and then start looking
for the delimeter (if you use one).  Or you can just have
everything in binary.

  > *Can u give an example.*

If you convert the 20-byte SHA1 to all lowercase ASCII (40
characters long), you can just use strcmp():

    int result=strcmp(str1, str2);

    if (result == 0) {
        /* str1 is the same as str2 */
    } else if (result > 0) {
        /* str1 is "bigger" than str2 */
    } else {
        /* str1 is "smaller" than str2 */
    }

If you are keeping the SHA1 value binary, you can use memcmp()
in a very similar way as above.
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>