select（NULL，NULL，NULL和＆timeout）只是等待给定的时间吗？(Does select(NULL, NULL, NULL, &timeout) just wait the giv

select（NULL，NULL，NULL和＆timeout）只是等待给定的时间吗？(Does select(NULL, NULL, NULL, &timeout) just wait the given time?)

给定代码中出现了以下行：

select(0, (fd_set *) NULL, (fd_set *) NULL, (fd_set *) NULL, &timeout);

http://linux.die.net/man/2/select

如果不对相应的事件类别观察文件描述符，则可以将三个文件描述符集合中的每一个指定为NULL。

所以我可以看到将NULL传递给它是有效的。 在这种情况下，它只能导致积极等待。

它是否正确？ 我有点不确定..

the following line has come to my eyes in given code:

select(0, (fd_set *) NULL, (fd_set *) NULL, (fd_set *) NULL, &timeout);

http://linux.die.net/man/2/select

Each of the three file descriptor sets may be specified as NULL if no file descriptors are to be watched for the corresponding class of events.

So I can see that it is valid to pass NULL into it. In that case it can only lead to do active waiting.

Is this correct? I am a bit unsure..

最满意答案

有些代码调用select（），其中所有三个组都为空，nfds为零，非NULL超时作为一种相当便携的方式以亚秒级精度进行休眠。

从这里开始 。

Some code calls select() with all three sets empty, nfds zero, and a non-NULL timeout as a fairly portable way to sleep with subsecond precision.

Taken from here.