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From: jimc@ucla-cs.UUCP
Newsgroups: net.lang
Subject: Re: Comments on this program please...
Message-ID: <7839@ucla-cs.ARPA>
Date: Mon, 2-Dec-85 19:04:18 EST
Article-I.D.: ucla-cs.7839
Posted: Mon Dec  2 19:04:18 1985
Date-Received: Thu, 5-Dec-85 06:47:52 EST
References: <2389@ukma.UUCP>
Reply-To: jimc@ucla-cs.UUCP (Jim Carter)
Organization: UCLA Computer Science Department
Lines: 65

In article <2389@ukma.UUCP> david@ukma.UUCP (David Herron, NPR Lover) writes:
>Everybody I've shown this program to has *groaned* ...
>I think it's *cute*!
>#include <stdio.h>
>main()
>{
>	register int r, o, u, t, e;
>	while ((r = getchar()) != EOF) {
>		if (r == 'R')
>			if ((o = getchar()) == 'O')
>				if ((u = getchar()) == 'U')
>					if ((t = getchar()) == 'T')
>						if ((e = getchar()) == 'E')
>							printf("\nROUTE");
>						else
>							printf("ROUT%c", e);
>					else
>						printf("ROU%c", t);
>				else
>					printf("RO%c", u);
>			else
>				printf("R%c", o);
>		else
>			putchar(r);
>	}
>	putchar('\n');
>}
Yes, indeed, the above program is aesthetically disgusting.  But what is
wrong with it in practice?  1.  It works only for that one pattern (not 
that files are often wiped like that, but let's keep our standards
up).  2.  The multiple if's and library calls can get lengthy on some mach-
ines.  3.  Using printf is expensive when you just want to concatenate
strings on the way out.  Here is a looping version.  Isn't this one just
as cute?

#include <stdio.h>
main(an, av)
  int an;
  char *av[];           /*When the pattern av[1] is found in stdin, a new-
                         *line is put in front of it, the result going to
                         *stdout. */
{
  register char c, *p, *r;
  if (an < 2) {puts("Usage: gorf pattern"); exit(1);}  /*Idiotproof*/
  for (p = av[1]; ; ) {
    c = getchar();
    if (c == *p && c != '\0') {  /*Char does match pattern (last term is
                         *nitpick overkill since \0 unlikely in text).
                         *Note, EOF doesn't match pattern.*/
      if (*++p == '\0') putchar('\n'); /*Found whole pattern, write new-
                         *line before it.  Pattern dumped on next char.*/
    } else {            /*Char. doesn't match pattern*/
      for (r = av[1]; r < p; ) putchar(*r++);  /*Dump portion of pattern,
                             *if any, that was matched*/
      if (c == EOF) break;
      putchar(c);       /*After which, write non-matching char.*/
      p = av[1];        /*Again start looking for pattern*/
    }
  }
}
(Bug: if the pattern is ROUTE and the text is ROUROUTE, the pattern will
be missed.  This is an easy fix.  But if the pattern is TINTINABULATION
and the text is TINTINTINABULATION, even with the above fix the pattern
will be missed.  It could be seen only with long and expensive pattern
checking -- or does someone see a smart way to do it?