pthread_exit() 参数的不正确使用

    #include<stdio.h>
    #include<pthread.h>
    #include<unistd.h>
    #include<stdlib.h>
    struct foo{
        int a,b,c,d;
    };

    void printfoo(const char *s,const struct foo *fp)
    {
        printf("s is %s\n",s);
        printf("structure at 0x%x\n",(unsigned)fp);
        printf("foo.a=%d\n",fp->a);
        printf("foo.b=%d\n",fp->b);
        printf("foo.c=%d\n",fp->c);
        printf("foo.d=%d\n",fp->d);
    }
    void *thr_fn1(void *arg)
    {
        struct foo foo={1,2,3,4};
        printfoo("thread 1:\n",&foo);
        pthread_exit((void *)&foo);//线程返回值存在foo，栈中，该函数结束释放
    }
    void * thr_fn2(void *arg)
    {
 
        printf("thread 2:ID is %d\n",pthread_self());
 
        pthread_exit((void *)0);
    }
    int main(void)
    {
        
        int err;
        pthread_t tid1,tid2;
        struct foo *fp;
        err=pthread_create(&tid1,NULL,thr_fn1,NULL);
        if(err!=0){
            printf("create thread 1 is failed\n",strerror(err));
            exit(1);
        }
        err=pthread_join(tid1,(void *)&fp);//fp存储被等待线程的返回值
        if(err!=0)
                printf("can't join thread1\n");
        sleep(1);
        err=pthread_create(&tid2,NULL,thr_fn2,NULL);
        if(err!=0)
        {
            printf("create thread 2 is failed\n");
             exit(1);
        }
        sleep(1);
        printfoo("parent :\n",&fp);//fp的内容是thr_fn1中的&foo，已被释放，此处打印的是野指针的内容。
        exit(0);
    }