Example of using functions in search.h

search_example.c

// gcc -g -O0 -lm -o /tmp/search_example /tmp/search_example.c
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#include <search.h>

int main(int argc, char* argv[]) {
	// Create a hash table with 255 entries.
	struct hsearch_data* htable = malloc(sizeof(struct hsearch_data*));
	hcreate_r(255, htable);

	// Insert pow(i,i) for i in range(0..255) inclusive into hash table.
	// Key is `i as char`, therefore 255 is maximum for this method of key derivation.
	for (int i = 0; i <= 255; i++) {
		// ENTRY type is defined in search.h
		ENTRY item;
		char* key = malloc(2);
		key[0] = i;
		item.key = key;
		double* data = calloc(1, sizeof(double));
		// Set void* item.data to double* data
		*data = (pow((double)i,(double)i)); item.data = data;
		ENTRY* unused; hsearch_r(item, ENTER, &unused, htable);
	}

	// Pointer to found entry
	ENTRY* found;
	ENTRY search;
	search.key = "\x8";
	hsearch_r(search, FIND, &found, htable);
	printf("found %f\n", *(double*)(found->data));
	search.key = "\xff";
	hsearch_r(search, FIND, &found, htable);
	printf("found %f\n", *(double*)(found->data));

	hdestroy_r(htable);

	return EXIT_SUCCESS;
}