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linux—selectÏê½â
selectϵͳµ÷ÓÃʱÓÃÀ´ÈÃÎÒÃǵijÌÐò¼àÊÓ¶à¸öÎļþ¾ä±úµÄ״̬±ä»¯µÄ¡£³ÌÐò»áÍ£ÔÚselectÕâÀïµÈ´ý£¬Ö±µ½±»¼àÊÓµÄÎļþ¾ä±úÓÐÒ»¸ö»ò¶à¸ö·¢ÉúÁË״̬¸Ä±ä¡£
¹ØÓÚÎļþ¾ä±ú£¬Æäʵ¾ÍÊÇÒ»¸öÕûÊý£¬Í¨¹ýsocketº¯ÊýµÄÉùÃ÷¾ÍÃ÷°×ÁË£º
int socket(int domain, int type, int protocol);
ÎÒÃÇ×îÊìϤµÄ¾ä±úÊÇ0¡¢1¡¢2Èý¸ö£¬0ÊDZê×¼ÊäÈ룬1ÊDZê×¼Êä³ö£¬2ÊDZê×¼´íÎóÊä³ö¡£0¡¢1¡¢2ÊÇÕûÊý±íʾµÄ£¬¶ÔÓ¦µÄFILE *½á¹¹µÄ±íʾ¾ÍÊÇstdin¡¢stdout¡¢stderr¡£
¼ÌÐøÉÏÃæµÄselect£¬¾ÍÊÇÓÃÀ´¼àÊÓij¸ö»òijЩ¾ä±úµÄ״̬±ä»¯µÄ¡£selectº¯ÊýÔ­ÐÍÈçÏ£º
int select (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
º¯ÊýµÄ×îºóÒ»¸ö²ÎÊýtimeoutÊÇÒ»¸ö³¬Ê±Ê±¼äÖµ¡£ÆäÀàÐÍÊÇstruct timeval *£¬¼´Ò»¸östruct timeval½á¹¹µÄ±äÁ¿µÄÖ¸Õ룬ËùÒÔÎÒÃÇÔÚ³ÌÐòÀïÒªÉùÃ÷Ò»¸östruct timeval tv;È»ºó°Ñ±äÁ¿tvµÄµØÖ·&tv´«µÝ¸øselectº¯Êý¡£struct timeval½á¹¹ÈçÏ£º
struct timeval
{
       long tv_sec;  //seconds
       long tv_usec; //microseconds
}£»
µÚ2¡¢3¡¢4Èý¸ö²ÎÊýÊÇÒ»ÑùµÄÀàÐÍ;fd_set *,¼´ÎÒÃÇÔÚ³ÌÐòÀïÒªÉêÇ뼸¸öfd_setÀàÐ͵ıäÁ¿£¬±ÈÈçrdfds£¬wtfds£¬exfds£¬È»ºó°ÑÕâ¸ö±äÁ¿µÄµØÖ·&rdfds,&wtfds,&exfds´«µÝ¸øselectº¯Êý¡£ÕâÈý¸ö²ÎÊý¶¼ÊÇÒ»¸ö¾ä±úµÄ¼¯ºÏ£¬µÚÒ»¸ördfdsÊÇÓÃÀ´±£´æÕâÑùµÄ¾ä±úµÄ:µ±¾ä±úµÄ״̬±ä³É¿É¶Áʱϵͳ¾Í¸æËßselectº¯Êý·µ»Ø£¬Í¬ÀíµÚ¶þ¸öº¯ÊýÊÇÖ¸ÏòÓоä±ú״̬±ä³É¿Éдʱϵͳ¾Í»á¸æËßselectº¯Êý·µ»Ø£¬Í¬ÀíµÚÈý¸ö²ÎÊýexfdsÊÇÌØÊâÇé¿ö£¬¼´¾ä±úÉÏÓÐÌØÊâÇé¿ö·¢Éúʱϵͳ»á¸æËßselectº¯Êý·µ»Ø¡£ÌØÊâÇé¿ö±ÈÈç¶Ô·½Í¨¹ýÒ»¸ösocket¾ä±ú·¢À´Á˽ô¼±Êý¾Ý¡£Èç¹ûÎÒÃdzÌÐòÀïÖ»Ïë¼ì²âij¸ösocketÊÇ·ñÓÐÊý¾Ý¿É¶Á£¬ÎÒÃÇ¿ÉÒÔÕâÑù£º
fd_set  rdfds;
struct timeval tv;
int ret;
FD_ZERO(&rdfds);
FD_SET(socket, &rdfds);
tv.tv_sec = 1;
tv.tv_uses = 500;
ret = select (socket + 1, %rdfds, NULL, NULL, &tv);
if(ret < 0) perror (“select”);
else if (ret = = 0) printf(“time out”);
else {
       printf(“ret = %d\n”,ret);
       if(FD_ISSET(socket, &rdfds)){
   


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