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#include <stdio.h>
#include <string.h> // strdup, strcmp
#include <stdlib.h> // malloc, free
/* The C Programming Language: 2nd Edition
*
* Exercise 6-6: Implement a simple version of the `#define` processor
* (i.e., no arguments) suitable for use with C programs, based on the
* routines of this section. You may also find getch() and ungetch()
* helpful.
*
* Notes: The routines this exercise is talking about are lookup() and
* install(), which were used in 6-5. It also depends on the 'nlist'
* data structure that those functions used. It's unclear what is meant
* by "#define processor", so I opted for a simple string replacement
* implementation. It only accepts one alpha-numeric name and one alpha-
* numeric replacement, so nowhere *near* correctly supporting #define,
* but it fulfills the requirements. There's room for improvement here,
* for sure.
*/
#define HASHSIZE 101
#define MAXWORD 65
#define BUFSIZE 40
struct nlist {
struct nlist *next;
char *name;
char *defn;
};
static struct nlist *hashtab[HASHSIZE];
enum states {
NORMAL,
INQUOTE,
COMMENT_PART_IN,
COMMENT_PART_OUT,
ONELINE_COMMENT,
INCOMMENT
};
static char buf[BUFSIZE];
static int bufp = 0;
int state = NORMAL;
unsigned hash(char *);
struct nlist *install(char *, char *);
struct nlist *lookup(char *);
int getch(void);
void ungetch(int);
int getword(char *, int);
int main() {
char *word = malloc(sizeof(char) * MAXWORD);
struct nlist *def;
int define_phase = 0;
char *name;
char *desc;
while (getword(word, MAXWORD) != EOF) {
if (state == NORMAL && strcmp(word, "#define") == 0) {
define_phase = 1;
printf("%s", word);
continue;
}
if (define_phase == 1) {
name = strdup(word);
define_phase = 2;
printf("%s", word);
continue;
}
if (define_phase == 2) {
desc = strdup(word);
define_phase = 0;
printf("%s", word);
install(name, desc);
continue;
}
if (state == NORMAL && (def = lookup(word)) != NULL) {
printf("%s", def->defn);
continue;
}
printf("%s", word);
}
}
/* form hash value for string s */
unsigned hash(char *s) {
unsigned hashval;
for (hashval = 0; *s != '\0'; s++) {
hashval = *s + 31 * hashval;
}
return hashval % HASHSIZE;
}
/* Look for s in hashtab */
struct nlist *lookup(char *s) {
struct nlist *np;
for (np = hashtab[hash(s)]; np != NULL; np = np->next) {
if (strcmp(s, np->name) == 0) {
return np;
}
}
return NULL;
}
/* put name and defn in hashtab */
struct nlist *install(char *name, char *defn) {
struct nlist *np;
unsigned hashval;
if ((np = lookup(name)) == NULL) {
np = (struct nlist *) malloc(sizeof(*np));
if (np == NULL || (np->name = strdup(name)) == NULL) {
return NULL;
}
hashval = hash(name);
np->next = hashtab[hashval];
hashtab[hashval] = np;
} else {
free((void *) np->defn);
}
if ((np->defn = strdup(defn)) == NULL) {
return NULL;
}
return np;
}
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 getword(char *word, int lim) {
int c;
char *w = word;
while (isspace(c = getch())) {
if (c == '\n' && state == ONELINE_COMMENT) {
state = NORMAL;
}
putchar(c);
}
if (c != EOF) {
*w++ = c;
} else {
return EOF;
}
switch (c) {
case '/':
switch (state) {
case NORMAL:
state = COMMENT_PART_IN;
break;
case COMMENT_PART_IN:
state = ONELINE_COMMENT;
break;
case COMMENT_PART_OUT:
state = NORMAL;
break;
}
break;
case '*':
switch (state) {
case INCOMMENT:
state = COMMENT_PART_OUT;
break;
case COMMENT_PART_IN:
state = INCOMMENT;
break;
}
break;
case '"':
switch (state) {
case NORMAL:
state = INQUOTE;
break;
case INQUOTE:
state = NORMAL;
break;
}
break;
}
if (!isalnum(c) && c != '#') {
*w = '\0';
return c;
}
for (; --lim > 0; w++) {
if (!isalnum(*w = getch())) {
ungetch(*w);
break;
}
}
*w = '\0';
return word[0];
}
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