Solve Exercise 6-01: Enhanced `getword`

This exercise improved my understanding of identifying comments and
quotes by focusing on edge cases.

1 files changed, 170 insertions, 0 deletions

diff --git a/ch6/6-01_getword-enhanced.c b/ch6/6-01_getword-enhanced.c
new file mode 100644
index 0000000..c040d1e
--- /dev/null
+++ b/ch6/6-01_getword-enhanced.c
@@ -0,0 +1,170 @@
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 6-1: Our version of `getword` does not properly handle underscores,
+ * string constants, comments, or preprocessor control lines. Write a better
+ * version.
+ *
+ * Notes: Preprocessor lines and one-line comments should be treated the same by
+ * ignoring everything after the beginning. Underscores need to be treated like
+ * part of the word, otherwise identifiers such as 'if_else' will get added to
+ * the list. Anything inside quotes and multi-line comments needs to be ignored,
+ * with a state variable to help us figure out what's going on.
+ */
+
+
+#define MAXWORD 100
+#define BUFSIZE 1000
+
+struct key {
+	char *word;
+	int count;
+} keytab[] = {
+	"auto",     0,
+	"break",    0,
+	"case",     0,
+	"char",     0,
+	"const",    0,
+	"continue", 0,
+	"default",  0,
+	"else",     0,
+	"enum",     0,
+	"for",      0,
+	"if",       0,
+	"int",      0,
+	"long",     0,
+	"return",   0,
+	"short",    0,
+	"signed",   0,
+	"static",   0,
+	"struct",   0,
+	"switch",   0,
+	"typedef",  0,
+	"unsigned", 0,
+	"void",     0,
+	"volatile", 0,
+	"while",    0
+};
+
+#define NKEYS (sizeof keytab / sizeof(struct key))
+
+char buf[BUFSIZE];
+int bufp = 0;
+enum states {
+	NORMAL,
+	INQUOTE,
+	INCOMMENT
+};
+int state = NORMAL;
+
+int getch(void);
+void ungetch(int);
+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 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;
+	}
+}
+
+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;
+	char *w = word;
+	while (isspace(c = getch())) {
+	}
+	if (c != EOF && c != '#' && c != '"' && c != '/' && c != '*') {
+		*w++ = c;
+	}
+	if (c == '*' && state == INCOMMENT) {
+		if ((c = getch()) == '/') {
+			state == NORMAL;
+			return '/';
+		}
+	}
+	/* Ignore comments */
+	if (c == '/') {
+		c = getch();
+		if (c == '/') {
+			while ((c = getch()) != EOF && c != '\n') {
+			}
+			return '*';
+		}
+		if (c == '*') {
+			state = INCOMMENT;
+			return '*';
+		}
+	}
+	/* Handle quotes */
+	if (c == '"') {
+		state = INQUOTE;
+	}
+	if (state == INQUOTE) {
+		while ((c = getch()) != '"' && c != EOF) {
+		}
+		state = NORMAL;
+	}
+	/* Ignore preprocessor lines */
+	if (c == '#') {
+		while ((c = getch()) != '\n' && c != EOF) {
+		}
+	}
+	/* Add exceptions for underscores */
+	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];
+}