Simon said:
Does anybody have a solution or a hint for Exercise 5 of Chapter
15 of K.N. King's book C Programming: A Modern Approach? I spent
all of yesterday evening staring at it and drooling. The author
sure does have a knack for making me feel like a dumbass, or maybe
it's just that I am.
The following code pads out sentences with extra spaces between
words so that each line takes up the same amount of space on
screen. As is, the code will favour the end of the line when
distributing the extra spaces. The task is to modify it so that
it alternates between distribution of the extra spaces favouring
the end of the line and the beginning of the line.
Here is something I threw together some time ago. I never did the
alternation part, but I did arrange to keep track of when needed.
Doing that will basically require a suitable buffer, rather than
simple stream output with putc.
/* ----- 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. 2003-01-28.
Released to public domain by:
<mailto:
[email protected]>
*/
#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
= '\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 */