ch06-searchemp.c

linux编程精髓 源代码

/* ch06-searchemp.c --- Demonstrate bsearch(). */

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

struct employee {
	char lastname[30];
	char firstname[30];
	long 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;
	else if (e1->emp_id == e2->emp_id)
		return 0;
	else
		return 1;
}

/* print_employee --- print an 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 --- demonstrate sorting */

int main(int argc, char **argv)
{
#define NPRES 10
	struct employee presidents[NPRES];
	int i, npres;
	char buf[BUFSIZ];
	struct employee *the_pres;
	struct employee key;
	int id;
	FILE *fp;

	if (argc != 2) {
		fprintf(stderr, "usage: %s datafile\n", argv[0]);
		exit(1);
	}

	if ((fp = fopen(argv[1], "r")) == NULL) {
		fprintf(stderr, "%s: %s: could not open: %s\n", argv[0],
				argv[1], strerror(errno));
		exit(1);
	}

	/* Very simple code to read data: */
	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);
	}
	fclose(fp);

	/* npres is now number of actual lines read. */

	/* First, sort by id */
	qsort(presidents, npres, sizeof(struct employee), emp_id_compare);

	/* Print output */
	printf("Sorted by ID:\n");
	for (i = 0; i < npres; i++) {
		putchar('\t');
		print_employee(& presidents[i]);
	}

	for (;;) {
		printf("Enter ID number: ");
		if (fgets(buf, BUFSIZ, stdin) == NULL)
			break;

		sscanf(buf, "%d\n", & id);
		key.emp_id = id;
		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", id);
	}

	putchar('\n');  /* Print a newline on EOF. */

	exit(0);
}