Exercise 6.01

Page 136

Our version of getword does not properly handle underscores, string constants, comments, or preprocessor control lines. Write a better version.

/* What exactly is 'proper' handling here? In this particular context, none of those
 * things are useful. I assume I am meant to be modifying `getword` to be applicable in
 * a broader context. My intepretation is that underscores should be allowed in words,
 * and that words should be ignored if in comments, strings, or preprocessor control
 * lines. */

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

#define MAXWORD 100
#define NKEYS (sizeof keytab / sizeof(struct key))

struct key {
	char *word;
	;
	int count;
} keytab[] = { { "auto", 0 },	  { "break", 0 },    { "case", 0 },
	       { "char", 0 },	  { "const", 0 },    { "continue", 0 },
	       { "default", 0 },  { "do", 0 },	     { "double", 0 },
	       { "else", 0 },	  { "enum", 0 },     { "extern", 0 },
	       { "float", 0 },	  { "for", 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 },   { "typedef", 0 },
	       { "union", 0 },	  { "unsigned", 0 }, { "void", 0 },
	       { "volatile", 0 }, { "while", 0 } };

int getword(char *, int);
int binsearch(char *, struct key *, int);

int main()
{
	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;
}

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;
}

int getword(char *word, int lim)
{
	int c, getch(void);
	void ungetch(int);
	char *w = word;

	while (isspace(c = getch()))
		;

	/* Skip comments, strings, preprocessor statements */
	char *term = "";
	if (c == '/') {
		c = getch();
		if (c == '/') {
			term = "\n";
		} else if (c == '*') {
			term = "*/";
		} else {
			ungetch(c);
			c = '/';
		}
	} else if (c == '#') {
		term = "\n";
	} else if (c == '"') {
		term = "\"";
	}
	for (int i = 0; term[i] != '\0' && (c = getch()) != EOF;) {
		if (c == term[i]) {
			i++;
		}
	}

	if (c != EOF) {
		*w++ = c;
	}

	if (!isalpha(c) && c != '_') {
		*w = '\0';
		return c;
	}

	for (; --lim > 0; w++) {
		if (!isalnum(*w = getch()) && *w != '_') {
			ungetch(*w);
			break;
		}
	}
	*w = '\0';

	return word[0];
}

#define BUFSIZE 100
char buf[BUFSIZE];
int bufp = 0;

int getch(void)
{
	return (bufp > 0) ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
	if (bufp >= BUFSIZE) {
		printf("ungetch: too many characters\n");
	} else {
		buf[bufp++] = c;
	}
}