#include <stdio.h>
#include <errno.h>
#include <stdlib.h> 

struct  employee {
	char lastname[30];
	char firstname[30];
	int emp_id;
	time_t start_date;
};

/* emp_id_compare --- compare by ID */ 
int emp_id_compare(const void *e1p, const void *e2p) {
	const struct employee *e1, *e2;
	
	e1 = (const struct employee *) e1p;
	e2 = (const struct employee *) e2p;
	
	if (e1->emp_id < e2->emp_id) return -1;
	if (e1->emp_id > e2->emp_id) return 1;
	else return 0;
}

/* print_employee() --- print employee-structure */ 
void print_employee(const struct employee *emp) {
	printf("%s %s\t%d\t%s", emp->lastname, emp->firstname, emp->emp_id, ctime(emp->start_date));
}

/* main --- demonstarte sorting and bsearching */ 
int main(int argc, char **argv) {
#define NPRES 10
	char *myname = argv[0];
	struct employee presidents[NPRES];
	int i, npres;
	char buf[BUFSIZ];
	struct employee *the_pres; /* pointer-variable for found-item */  
	struct employee key; /* structure for search-criteria 	*/
	int id; /* what we want to search for */ 
	FILE *fp; /* we need a file for president-data, because we use stdin to prompt for the DI */ 
	
	/* check for arguments */ 
	if (argc != 2) {
		fprintf(stderr, "usage: %s filename\n", myname);
		exit(1);
	}
	
	/* Open the file */ 
	if ((fp = fopen(argv[1], "r")) == NULL) {
		fprintf(stderr, "%s: %s: could not open: %s", myname, argv[1], strerror(errno));
		exit(1);
	}
	
	/* read data from file */ 
	for (npres = 0; (npres < NPRES) && fgets(buf, BUFSIZ, fp) != NULL; npres++) {
		sscanf(buf, "%s %s %ld %ld", presidents[npres].lastname, presidents[npres].firstname,
			presidents[npres].emp_id, presidents[npres].start_date);
	}
	
	/* close the file */ 
	fclose(fp);
	
	/* npres is now the number of president-items read */ 
	
	/* Sort presidents by id */ 
	qsort(presidents, npres, sizeof(struct employee), emp_id_compare);
	
	/* print sorted array */ 
	printf("Sorted by ID:\n");
	for (i = 0; i<npres; i++) {
		putchar('\t');
		print_employee(&presidents[i]);
	}
	
	/* infinite searching loop */ 
	for (;;) {
		printf("Enter ID: ");
		if (fgets(buf, BUFSIZ, stdin) == NULL) break; /* read from stdin and exit on EOF */ 
		sscanf(buf, "%d\n", &id);
		
		key.emp_id = id; /* set search-criteria */ 
		
		/* set the_pres pointer to the pointer returned by bsearch() */  
		the_pres = (struct employee *) bsearch(&key, presidents, npres, sizeof(struct employee), emp_id_compare);
		
		if (the_pres != NULL) {
			printf("Found: ");
			print_employee(the_pres);
		}
		else {
			printf("Employee with ID %d not found!\n", key.emp_id);
		}
	}
	putchar('\n'); /* A final new line on EOF */
	exit(0);   
}