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From: eric@snark.UUCP (Eric S. Raymond)
Newsgroups: misc.misc,comp.lang.c
Subject: Printing binary (was: Re: Why college?)
Message-ID: <235@snark.UUCP>
Date: Mon, 19-Oct-87 12:34:46 EDT
Article-I.D.: snark.235
Posted: Mon Oct 19 12:34:46 1987
Date-Received: Wed, 21-Oct-87 00:33:22 EDT
References: <35@ateng.UUCP> <3194@sol.ARPA> <2783@xanth.UUCP>
Organization: Benevolent Space Xist Retirement Home
Lines: 39
Summary: Here's a neat hack
Xref: mnetor misc.misc:1950 comp.lang.c:5034

In article <148@artsvax.UUCP>, mike@artsvax.UUCP (Michael Czeiszperger) writes:
> The variable five is certainly stored in binary, even though it represents
> an integer.  A more plausible interpretation in a test situation would be
> to print each of the binary bits out in ascii, so that the output for an 
> integer 5 (assuming a large machine where an integer is 4 bytes) would be:
> 
> 00000000000000000000000000000101

I thought about the standard ways to do this, (essentially, crack the sucker
into powers-of-two internally via repeated integer-divide and modulo
operations) went *ugh*, and then had a flash that gave me an amusing
alternate solution. Here it is: (warning! this is untested and off-the-cuff)

#include "stdio.h"

void bprint(n, fp)
/* print n in binary to given fp */
int	n;
FILE	*fp;
{
    static char *nybbles =
    {
	"0000", "0001", "0010", "0011",	"0100", "0101", "0110", "0111",
	"1000", "1001", "1010", "1011",	"1100", "1101", "1110", "1111",
    };
    static char hexdigits = "0123456789abcdef";

    char foobuf[BUFSIZ], *cp;	/* BUFSIZ from stdio.h */

    (void) sprintf(cp = foobuf, "%x", n);
    while (*cp)
	(void) fputs(nybbles[strchr(hexdigits, *cp++) - hexdigits], fp);
}

Le voila! Let the C libraries do the work whenever you can, I always say...
-- 
      Eric S. Raymond
      UUCP:  {{seismo,ihnp4,rutgers}!cbmvax,sdcrdcf!burdvax,vu-vlsi}!snark!eric
      Post:  22 South Warren Avenue, Malvern, PA 19355    Phone: (215)-296-5718