6-1.c

/*
 * Exercise 6-1. Our version of getword does not properly handle underscores,
 * string constants, comments, or preprocessor control lines. Write a better
 * version.
 *
 * By Faisal Saadatmand
 */

#include <ctype.h>
#include <stdio.h>
#include <string.h>

#define MAXWORD  100
#define BUFSIZE  100
#define NKEYS (int) (sizeof keytab / sizeof keytab[0])

/* types */
struct key {
	char *word;
	int count;
};

/* functions */
int binsearch(char *, struct key[], int);
int getword(char *, int);

/* globals */
int buf[BUFSIZE];         /* buffer from ungetch */
int bufp = 0;             /* next free position in buf */

struct key keytab[] = {
	{ "auto", 0 },
	
	{ "case", 0 },
	{ "char", 0 },
	{ "const", 0 },
	{ "continue", 0 },
	{ "default", 0 },
	{ "do", 0 },
	{ "double", 0 },
	{ "else", 0 },
	{ "enum", 0 },
	{ "extern", 0 },
	{ "float", 0 },
	{ "goto", 0 },
	{ "if", 0 },
	{ "int", 0 },
	{ "long", 0 },
	{ "register", 0 },
	{ "return", 0 },
	{ "short", 0 },
	{ "signed", 0 },
	{ "sizeof", 0 },
	{ "static", 0 },
	{ "struct", 0 },
	{ "switch", 0 },
	{ "typeof", 0 },
	{ "union", 0 },
	{ "unsigned", 0 },
	{ "void", 0 },
	{ "volatile", 0 },
	{ "while", 0 },
};

/* binsearch: find word in tab[0]...tab[n-1] */
int binsearch(char *word, struct key tab[], int n)
{
	int cond;
	int low, high, mid;

	low = 0;
	high = n - 1;
	while (low <= high) {
		mid = (low + high) / 2;
		if ((cond = strcmp(word, tab[mid].word)) < 0)
			high = mid - 1;
		else if (cond > 0)
			low = mid + 1;
		else
			return mid;
	}
	return -1;
}

/* getword: get next word or character from input */
int getword(char *word, int lim)
{
	int c, getch(void);
	void ungetch(int);
	char *w = word;

	while (isspace(c = getch()))
		;
	if (c != EOF)
		*w++ = c;
	if (isalpha(c) || c == '_' || c == '#') {
		for ( ; --lim > 0; ++w)
			if (!isalnum(*w = getch()) && *w != '_') {
				ungetch(*w);
				break;
			}
	} else if (c == '\'') /* skip character constants */
		while ((c = getch()) != '\'')
			;
	else if (c == '\"')  { /* skip string constants */
		while ((c = getch()) != '\"')
			if (c == '\\')
				getch();
	} else if (c == '/' && (c = getch()) == '*') /* skip comments */
		while ((c = getch()) != EOF)
			if (c == '*' && (c = getch()) == '/')
				break;
	*w ='\0';
	return c;
}

/* get a (possibly pushed back) character */
int getch(void)
{
	return (bufp > 0) ? buf[--bufp] : getchar();
}

/* push character back on input */
void ungetch(int c)
{
	if (bufp >= BUFSIZE)
		printf("ungetch: too many characters\n");
	else
		buf[bufp++] = c;
}

/* count C keywords */
int main(void)
{
	int n;
	char word[MAXWORD];

	while (getword(word, MAXWORD) != EOF)
		if (isalpha(word[0]))
			if ((n = binsearch(word, keytab, NKEYS)) >= 0)
				++keytab[n].count;
	for (n = 0; n < NKEYS; ++n)
		if (keytab[n].count > 0)
			printf("%4d %s\n", keytab[n].count, keytab[n].word);
	return 0;
}