t.c

#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define	NELEM(x)	(sizeof(x) / sizeof(*(x)))

// MUST be sorted
const char *haystack[] = {
	"bar",
	"foo",
	"oni",
};

int
strcmp_wrap(const void * a, const void *b)
{
	const char *x = *((const char **)a);
	const char *y = *((const char **)b);
	return (strcmp(x, y));
}

int
main(int argc, char **argv)
{
	if (argc != 2)
		errx(EXIT_FAILURE, "usage %s KEY", argv[0]);

	const char *needle = argv[1];
	const char *found = bsearch(&needle, haystack, NELEM(haystack),
		    sizeof(*haystack), strcmp_wrap);

	if (found)
		(void)printf("I CAN HAZ %s.\n", needle);
	else
		(void)printf("I CAN NOT HAZ %s.\n", needle);

	return (found ? EXIT_SUCCESS : EXIT_FAILURE);
}