Hashtable macro in C. TYPE is the variable type, KEY_SIZE is the maximum key string size, TABLE_SIZE is the maximum table size. (must be a prime number)

hashtable.c

#ifndef HASHTABLE_H_
#define HASHTABLE_H_

#include <string.h>

unsigned int djb2(const char *str){
	unsigned long hash = 5381;
	int c;

	while ((c = *str++)) {
		hash = ((hash << 5) + hash) + c;
	}
	
	return hash;
}

#define HASHTABLE(TYPE, KEY_SIZE, TABLE_SIZE) \
typedef struct { \
	char key[KEY_SIZE]; \
	TYPE value; \
} bucket_t_##TYPE; \
 \
bucket_t_##TYPE table_##TYPE[TABLE_SIZE]; \
 \
int table_set_##TYPE(const char *key, TYPE value) { \
	unsigned int i, index; \
	 \
	if (!key) return 0; \
	index = djb2(key) % TABLE_SIZE; \
	 \
	for (i=0; i<TABLE_SIZE; i++) { \
		int pos = index + i; \
		\
		if (pos >= TABLE_SIZE) { \
			pos -= TABLE_SIZE; \
		} \
		 \
		if (!table_##TYPE[pos].key[0]) { \
			strncpy(table_##TYPE[pos].key, key, sizeof(table_##TYPE[pos].key)); \
			table_##TYPE[pos].value = value; \
			return 1; \
		} \
		\
		if (strcmp(table_##TYPE[pos].key, key) == 0) { \
			strncpy(table_##TYPE[pos].key, key, sizeof(table_##TYPE[pos].key)); \
			table_##TYPE[pos].value = value; \
			return 1; \
		} \
	} \
	 \
	return 0; \
} \
 \
int table_get_##TYPE(const char *key, TYPE *value) { \
	unsigned int i, index; \
	 \
	if (!key || !value) return 0; \
	index = djb2(key) % TABLE_SIZE; \
	 \
	for (i=0; i<TABLE_SIZE; i++) { \
		int pos = index + i; \
		 \
		if (pos >= TABLE_SIZE) { \
			pos -= TABLE_SIZE; \
		} \
		 \
		if (!table_##TYPE[pos].key[0]) { \
			return 0; \
		} \
		 \
		if (strcmp(table_##TYPE[pos].key, key) == 0) { \
			*value = table_##TYPE[pos].value; \
			return 1; \
		} \
	} \
	 \
	return 0; \
} \

#endif

/*///////////////////////////////////
	
		Testing:
		
///////////////////////////////////*/

HASHTABLE(int, 32, 211)

typedef char *string;
HASHTABLE(string, 32, 211)

struct Example {
	int a;
	float b;
};

typedef struct Example Example;
HASHTABLE(Example, 16, 211)

#include <stdio.h>

int main() {
	int a, b, c;
	string str1, str2, str3;
	Example x, y, w, z;
	
	x.a = 123;
	x.b = 0.123;
	y.a = 69;
	y.b = 6.9;
	
	table_set_int("1", 1);
	table_set_int("2", 2);
	table_set_int("3", 3);
	
	table_set_string("foo", "bar");
	table_set_string("one", "two");
	table_set_string("->", "<-");
	
	table_set_Example("myStruct", x);
	table_set_Example("myStruct2", y);
	
	table_get_int("1", &a);
	table_get_int("2", &b);
	table_get_int("3", &c);
	
	table_get_string("foo", &str1);
	table_get_string("one", &str2);
	table_get_string("->", &str3);
	
	table_get_Example("myStruct", &w);
	table_get_Example("myStruct", &z);
	
	printf("%i\n", a);
	printf("%i\n", b);
	printf("%i\n", c);
	
	printf("%s\n", str1);
	printf("%s\n", str2);
	printf("%s\n", str3);
	
	printf("%i %f\n", w.a, w.b);
	printf("%i %f\n", z.a, z.b);
	
	return 0;
}