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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: K&R, 2nd edition, Brian's concerns with ``char c = EOF''
Date: Wed, 15 Dec 2021 00:31:35 -0800
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Xref: csiph.com comp.lang.c:163841

Dave Dunfield <dave.dunfield@gmail.com> writes:

> [...]

For future reference here is a short C program that does
base64 encoding.


/***  b64e.c - base64 encode stdin to stdout.             */
/***  NOTE:  This program assumes characters are 8 bits.  */

#include <stdio.h>

static char A[] = {
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
};

int
main( void ){
    int c;
    unsigned long  b = 0,  n = 0,  k = 0;
    char out[ 73 ];

    while(  c = getchar(),  c != EOF  ){
        b = (b<<8) + c,  n += 8;
        do {
            if(  k > 71  )  out[k] = 0,  puts( out ),  k = 0;
            n -= 6;
            out[ k++ ] = A[ b >>n &63 ];
        } while(  n > 5  );
    }

    if(  n > 0  )  out[ k++ ] = A[ b <<(6-n) &63 ];

    if(  k > 0  )  out[k] = 0,  puts( out ),  k = 0;
    else           puts( "====" );

    return  0;
}