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From: em@dce.ie (Eamonn McManus)
Newsgroups: comp.text.tex
Subject: Re: Two problems with my directory format
Message-ID: <loranawduh@dce.ie>
Date: 12 Feb 91 22:04:58 GMT
References: <59099@eerie.acsu.Buffalo.EDU>
Organization: Datacode Communications Ltd, Dublin, Ireland
Lines: 39

xiaofei@acsu.buffalo.edu (Xiaofei Wang) writes:
>Another thing is one has to enter the directory entry
>alphabetically manually. [I looked the phone.tex and my impression is
>it does not have ``auto ordering'' feature.]

Since TeX does not have primitives to compare two strings except for
equality, it is difficult to use it to do ordering.  Besides, doing it by
hand means that you can deal with peculiarities of your national language,
or put names with the forename first even though they are sorted by the
surname.

Of course, it's *possible* to write macros to compare strings (naively) and
to sort entries (e.g., by building a binary tree as the entries are read);
it's just not the sort of thing that's best done in TeX.

Here are some macros I wrote some time ago to compare strings
alphabetically.  \compare{string1}{string2} expands to 0, -1, or 1,
according as string1 is the same as, less than, or greater than string2,
respectively.  Both strings should consist entirely of plain characters
(not control sequences).

I took care that the comparison is done entirely in TeX's `mouth', so this
macro can be used in \ifnum and the like.

,
Eamonn

% compare.tex - macro to compare two strings
% By \'Eamonn McManus.  This file is not copyrighted.

\def\compare#1#2{\compcont#1\ \\#2\ \\}
\def\compcont#1#2\\#3#4\\{%
     \csname comp%
       \if #1#3\if #1\ same\else cont\fi
       \else \ifnum `#1<`#3less\else greater\fi \fi
     \endcsname #2\\#4\\}
\def\compsame#1\\#2\\{0}
\def\compless#1\\#2\\{-1}
\def\compgreater#1\\#2\\{1}