key_t ftok(const char *path,int id);

在下面的代码段中？

key_t key;
int shmid;

key = ftok("/home/beej/somefile3",'R');
shmid = shmget(key,1024,0644 | IPC_CREAT);

从我所了解的,访问给定的共享内存所需要的是shmid,而不是密钥.还是我错了？如果我们需要的是shmid,那么每次不只是创建一个随机密钥的要点是什么？

编辑

@ Beej’s Guide to Unix IPC可以看：

What about this key nonsense? How do
we create one? Well,since the type
key_t is actually just a long,you can
use any number you want. But what if
you hard-code the number and some
other unrelated program hardcodes the
same number but wants another queue?
The solution is to use the ftok()
function which generates a key from
two arguments.

阅读这个,这给我的印象是,需要附加到共享内存块是一个关键.但这不是真的吗？