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      int select(int n,fd_set * readfds,fd_set * writefds,fd_set * exceptfds,struct timeval * timeout);²ÎÊýn´ú±íÎļþÃèÊö´Ê¼Ó1£»²ÎÊýreadfds¡¢writefds ºÍexceptfds ³ÆÎªÃèÊö´Ê×飬ÊÇÓÃÀ´»Ø´«¸ÃÃèÊö´ÊµÄ¶Á£¬Ð´»òÀýÍâµÄ×´¿ö¡£ÏÂÃæµÄºêÌṩÁË´¦ÀíÕâÈýÖÖÃèÊö´Ê×éµÄ·½Ê½:
FD_CLR(inr fd,fd_set* set)£»ÓÃÀ´Çå³ýÃèÊö´Ê×ésetÖÐÏà¹Øfd µÄλ
FD_ISSET(int fd,fd_set *set)£»ÓÃÀ´²âÊÔÃèÊö´Ê×ésetÖÐÏà¹Øfd µÄλÊÇ·ñÎªÕæ
FD_SET£¨int fd,fd_set*set£©£»ÓÃÀ´ÉèÖÃÃèÊö´Ê×ésetÖÐÏà¹ØfdµÄλ
FD_ZERO£¨fd_set *set£©£»ÓÃÀ´Çå³ýÃèÊö´Ê×ésetµÄÈ«²¿Î»
      ²ÎÊýtimeoutΪ½á¹¹timeval£¬ÓÃÀ´ÉèÖÃselect()µÄµÈ´ýʱ¼ä£¬Æä½á¹¹¶¨ÒåÈçÏ£º
struct timeval
{
       time_t tv_sec;
       time_t tv_usec;
};
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       selectº¯ÊýÖ´Ðнá¹û£ºÖ´Ðгɹ¦Ôò·µ»ØÎļþÃèÊö´Ê״̬ÒѸıäµÄ¸öÊý£¬Èç¹û·µ»Ø0´ú±íÔÚÃèÊö´Ê״̬¸Ä±äǰÒѳ¬¹ýtimeoutʱ¼ä£¬Ã»Óзµ»Ø£»µ±ÓдíÎó·¢ÉúʱÔò·µ»Ø-1£¬´íÎóÔ­Òò´æÓÚerrno£¬´Ëʱ²ÎÊýreadfds£¬writefds£¬exceptfdsºÍtimeoutµÄÖµ±ä³É²»¿ÉÔ¤²â¡£´íÎó
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EINVAL ²ÎÊýn Ϊ¸ºÖµ¡£
ENOMEM ºËÐÄÄÚ´æ²»×ã
       ³£¼ûµÄ³ÌÐòƬ¶ÎÈçÏ£º
fs_set readset£»
FD_ZERO(&readset);
FD_SET(fd,&readset);
select(fd+1,&readset,NULL,NULL,NULL);
if(FD_ISSET(fd,readset){……}
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#include<sys/time.h>
#include<sys/types.h>
#include<unistd.h>
#include<string.h>
#include<std


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