Unix系统编程11-7的3处不解，求解释
下面是代码，有几处不明白的地方
红色的地方为表面不明白的地方
1
根据C语言先申明后引用的原则
strcut foo *fp[NASH];
foo是从哪里来的呢？
2
fp->f_next = fh[idx];
fh[idx] = fp->f_next;
这样2句同样的效果吗？还是另有所指向
3
fp->f_next = fh[idx];
fp->f_next等于结构体数组指针idx处，但是我有点不明白,idx之前的地址呢？ 指向不确定的位置吗？
#define NHASH 29
#define HASH(fp) (((unsigned long)fp)%NHASH)
struct foo *fh[NHASH];
pthread_mutex_t hashlock = PTHREAD_MUTEX_INITIALIZER;
struct foo
{
int f_count; /*protected by hashlock*/
pthread_mutex_t f_lock;
struct foo *f_next; /*protected by hashlock*/
int f_id;
/*...more stuff here...*/
};
/* allocate the object*/
struct foo
foo_alloc(void)
{
struct foo *fp;
int idx;
if ((fp = malloc(sizeof(struct foo))) != NULL)
{
fp->f_count = 1;
if (pthread_mutex_init(&fp->f_lock, NULL) != 0)
{
free(fp);
return NULL;
}
idx = HASH(fp);
pthread_mutex_lock(&hashlock);
fp->f_next = fh[idx];
fh[idx] = fp->f_next;
pthread_mutex_lock(&fp->f_lock);
pthread_mutex_unlock(&hashlock);
/* ...continue initialization...*/
}
return fp;
}
