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struct timeval
{
time_t tv_sec;
time_t tv_usec;
};
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FD_ZERO(&readset);
FD_SET(fd,&readset);
select(fd+1,&readset,NULL,NULL,NULL);
if(FD_ISSET(fd,readset){……}
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#include<unistd.h>
#include<string.h>
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