pthread.h 编译问题？

PIAZZJ

这是APUE 上的一个关于pthread的程序.可是我编译时gcc提示
phtread_create 未定义，可是pthread.h加了的吗！？也有 /usr/include/pthread.h 这个头文件！请路过的朋友能看看呀！3q!

#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

pthread_t ntid;
static void printids(char *);
static void *thr_fn(void *);

int
main(void)
{
  int err;
  err = pthread_create (&ntid, NULL,thr_fn, NULL);
  if (err != 0)
    printf ("ptherd_create error \n");
  printids ("main thread: ");
  sleep (1);
  exit (0);
}

void printids(char *s)
{
  pid_t         pid;
  pthread_t     tid;
  pid = getpid ();
  tid = pthread_self ();
  printf ("%s pid %u  tid %u  (0x%x)\n",
          s, (unsigned int)pid, (unsigned int)tid, (unsigned int)tid);
}

void *thr_fn(void *arg)
{
  printids ("new thread: ");
  return ((void *)0);
}

x11

-lpthread