Mike S wrote:[color=blue]
>
> I noticed a very slight logic error in the solution to K&R Exercise
> 1-22 on the the CLC-Wiki, located at
>
>
http://www.clc-wiki.net/wiki/KR2_Exercise_1-22
>
> The exercise reads as follows:
>
> "Write a program to 'fold' long input lines into two or more shorter
> lines after the last non-blank character that occurs before the n-th
> column of input. Make sure your program does something intelligent with
> very long lines, and if there are no blanks or tabs before the
> specified column."
>
> And this is the solution provided on the clc-wiki, due to Rick Dearman
> (note that I changed FOLDLENGTH to 25, in order to better show the
> algorithm's effect):
>[/color]
.... snip ...
Good for you. However, another approach to the problem is embedded
in the following, which I first published quite a while ago. Note
that a negative linelength parameter causes ragged right operation,
which is exactly the effect needed by the above exercize.
/* ----- justify.c -----
Filter text file, right justifying by inserting
spaces between words. Words are anything separated
by blanks, tabs, newlines, formfeeds, bell, etc.
The single (optional) parameter is the output line
length, and defaults to 65. Execution without any
input redirections causes a help message.
This is a quick and dirty utility.
Released to public domain by:
<mailto:cbfalconer@worldnet.att.net>
*/
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#define RHDEFAULT 65
#define RHMIN 20
static int rhcol; /* right hand column limit */
static int ragged; /* No rh justification, 0 init */
/* ------------------- */
/* This is very likely to be non-portable */
/* DOES NOT check fp open for reading */
/* NULL fp is considered a keyboard here! */
static int akeyboard(FILE *fp)
{
#ifndef __TURBOC__
# ifdef __STDC__
/* This dirty operation allows gcc -ansi -pedantic */
extern int fileno(FILE *fp);
extern int isatty(int fn);
# endif
#endif
return ((fp != NULL) && isatty(fileno(fp)));
} /* akeyboard */
/* ------------------- */
static void help(char *phrase1, char *phrase2)
{
if (phrase1) fprintf(stderr, "%s", phrase1);
if (phrase2) fprintf(stderr, "%s", phrase2);
fprintf(stderr, "\n"
"Usage: justify [rightmargin] <infile >outfile\n"
" The default rightmargin is 65\n"
" and values less than 20 are rejected\n"
"\n"
"A large value of rightmargin will effectively\n"
"convert all paragraphs into single lines\n"
"\n"
"A negative rightmargin causes ragged right\n"
"\n"
"A blank line delimits paragraphs\n");
} /* help */
/* ------------------- */
static int initialize(int argc, char *argv[])
{
long rightcol;
char *err;
if (akeyboard(stdin) || (argc > 2)) {
help(NULL, NULL);
return 0;
}
rhcol = RHDEFAULT;
if (2 == argc) {
rightcol = strtol(argv[1], &err, 10);
if (rightcol < 0) {
rightcol = -rightcol;
ragged = 1;
}
if ((err == argv[1]) || (rightcol < RHMIN)) {
help("Bad argument: ", argv[1]);
return 0;
}
else rhcol = rightcol;
}
return 1;
} /* initialize */
/* ------------------- */
static void cleanup(void)
{
} /* cleanup */
/* ------------------- */
/* ================================== */
/* Routines for text input and output */
/* ================================== */
static void skipblanks(FILE *f)
{
int ch;
while ( (' ' == (ch = getc(f))) || ('\t' == ch) ||
('\v' == ch) || ('\f' == ch) || ('\a' == ch) )
continue;
ungetc(ch, f);
} /* skipblanks */
/* ------------------- */
/* The file is assumed to hold no control chars */
/* other than \n \t \v \a and \f. A blank line */
/* marks a paragraph ending word */
static int nextword(FILE *f, char *buffer, int max)
{
int i, ch;
skipblanks(f);
if (EOF == (ch = getc(f))) return 0;
/* Detect paragraph endings as \n\n */
if ('\n' == ch) {
skipblanks(f); ch = getc(f);
if ('\n' == ch) { /* paragraph ending */
buffer[0] = buffer[1] = ch; /* wd = "\n\n" */
buffer[2] = '\0';
/* now we have to absorb any more blank lines */
do {
skipblanks(f); ch = getc(f);
} while ('\n' == ch);
ungetc(ch, f);
return 1;
}
}
/* now ch holds the first non-blank. Use all printable */
if (EOF == ch) return 0;
if (!isgraph(ch)) {
fprintf(stderr, "'%c', 0x%x WARN: Invalid character\n",
ch, (unsigned)ch);
}
i = 0;
do {
buffer[i++] = ch;
if (i >= max) { /* truncate over long words */
i--;
break; /* leaving ch for next word */
}
ch = getc(f);
} while (isgraph(ch));
ungetc(ch, f); /* save for next word, may be \n */
buffer[i] = '\0'; /* terminate string */
return 1;
} /* nextword */
/* ------------------- */
static void justify(char *ln, int wdgaps, int xtra, FILE *out)
{
int insert, i;
static int oddln = 0; /* for rt left blank insertion */
char ch;
#ifdef DEBUG
fprintf(out, "%2d %2d ", wdgaps, xtra);
#endif
insert = 0; oddln = !oddln;
if (wdgaps)
while (xtra > wdgaps) {
insert++; xtra -= wdgaps;
}
while ((ch = *ln++)) {
putc(ch, out);
if (' ' == ch) {
if (xtra) {
xtra--;
putc(' ', out);
}
for (i = insert; i; i--) putc(' ', out);
}
}
putc('\n', out);
} /* justify */
/* ------------------- */
static int filter(FILE *in, FILE *out)
{
char *buf;
char *ln;
int wdcount, lnlgh, wdlgh;
char *eop = "\n\n"; /* end of paragraph */
int done, endpar;
if (!(buf = malloc(rhcol+1))) exit(EXIT_FAILURE);
if (!(ln = malloc(rhcol+1))) exit(EXIT_FAILURE);
done = !nextword(in, buf, rhcol + 1);
endpar = !strcmp(buf, eop);
while (!endpar && !done) {
/* form paragraph */
wdlgh = strlen(buf);
wdcount = 0;
*ln = '\0'; lnlgh = 0;
while ((((lnlgh + wdlgh) < rhcol) || !lnlgh)
&& !done && !endpar) {
/* form a line */
if (lnlgh) ln[lnlgh++] = ' ';
strcpy(ln + lnlgh, buf);
lnlgh += wdlgh;
wdcount++;
done = !nextword(in, buf, rhcol + 1);
endpar = !strcmp(buf, eop);
wdlgh = strlen(buf);
}
/* dump the line, wdcount words */
if (endpar || done) lnlgh = rhcol;
if (ragged) fprintf(out, "%s\n", ln);
else justify(ln, wdcount-1, rhcol-lnlgh, out);
if (endpar) {
fputc('\n', out);
done = !nextword(in, buf, rhcol + 1);
endpar = !strcmp(buf, eop);
}
}
return 0;
} /* filter */
/* ------------------- */
int main(int argc, char *argv[])
{
if (!initialize(argc, argv)) return EXIT_FAILURE;
else {
(void)filter(stdin, stdout);
cleanup();
}
return 0;
} /* main */
--
"A man who is right every time is not likely to do very much."
-- Francis Crick, co-discover of DNA
"There is nothing more amazing than stupidity in action."
-- Thomas Matthews
