Combined hash and list

hashlist.c

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

#define SIZE 256

struct element {
	char *key;
	double value;

	struct element *bucket_next;
	struct element *list_next;
};

struct bucket {
	struct element *first;
	struct element *last;
};

struct bucket hashtable[SIZE];

struct element *list_last;
struct element *list_first;

int hash(char *key) {
	int h = 0;

	if (key) {
		if (key[0]) {
			h ^= key[0];
		}
	}

	return h;
}

void insert(char *key, double value) {
	struct element *e = malloc(sizeof(struct element));
	e->key   = key;
	e->value = value;

	e->bucket_next = 0;
	e->list_next   = 0;

	// Add element to list
	if (! list_first)
		list_first = e;
	if (list_last)
		list_last->list_next = e;
	list_last = e;

	// Add element to hashtable
	int h = hash(key);
	if (! hashtable[h].first) {
		hashtable[h].first = e;
		hashtable[h].last  = e;
	} else {
		hashtable[h].last->bucket_next = e;
		hashtable[h].last = e;
	}
}

void print_all() {
	struct element *p;
	for (p = list_first; p; p = p->list_next) {
		printf("%s => %f\n", p->key, p->value);
	}
}

int find(char *key, double *value) {
	int h = hash(key);

	struct element *e;
	for (e = hashtable[h].first; e; e = e->bucket_next) {
		if (0 == strcmp(key, e->key)) {
			*value = e->value;
			return 1;
		}
	}

	return 0;
}

void check_for(char *key) {
	double value;
        if (find(key, &value)) {
                printf("Found '%s' with value %f\n", key, value);
        } else {
                printf("Did not find value of '%s'\n", key);
        }
}

init() {
	int i;
	for (i=0; i<SIZE; i++) {
		hashtable[i].first = hashtable[i].last = 0;
	}

	list_first = list_last = 0;
}

main() {
	init();

	insert("pi", 3.14159265);
	insert("e", 2.718281828);
	insert("gamma", 0.577215664901);

	print_all();

	check_for("pi");
	check_for("psi");
	check_for("e");
	check_for("f");
	check_for("gamma");
	check_for("beta");
}