new_item()和new_menu()的问题

jsliu

#include <curses.h>
#include <menu.h>
......................(省略，同下)

ITEM *items[4];
MENU *menu;

char *a = "Haha",  *b = "Yeah";

items[0] = new_item(a, b);
items[1] = NULL;

menu = new_menu(items);
............................

#gcc test.c -o a -lcurses
.........: In function 'main':
: undefined reference to 'new_item'
.........: In function 'main':
: undefined reference to 'new_menu'
collect2: ld returned 1 exit status

请问，这是什么错误啊，怎么造成的？
我在/usr/include中有curses.h 和menu.h文件。
请各位朋友指点，谢谢