The use of select Learning to select, the following code found no obstruction. Select one return. Please experts advise. There is a parameter, in the end should be described at best, or the number of descriptors. [code]#include "Stdio.h>; #include "Sys/time.h>; #include "Sys/types.h>; #include "Unistd.h>; #include "Fcntl.h>; Int Main (void) ( Fd_set rfds; Struct timeval tv; Int retval; Int czw, ling; Czw=open ( "/home/czw/czw" O_RDONLY|O_NONBLOCK); LEAVES OF 13 SPECIES OF LAURACEAE Watch stdin (fd 0) to see when it has input. */ FD_ZERO (&rfds); FD_SET (czw, &rfds); LEAVES OF 13 SPECIES OF LAURACEAE Wail up to five seconds. */ Tv.tv_sec = 100; Tv.tv_usec = 0 Retval = select (czw+1, &rfds, NULL, NULL, &tv); LEAVES OF 13 SPECIES OF LAURACEAE Don 't rely on the value of tv now! */ Printf ( "retval = %d\n" retval); If (retval) Printf ( "Data is available now.\n"); LEAVES OF 13 SPECIES OF LAURACEAE FD_ISSET (0, &rfds) will be true. */ Else Printf ( "No data within five seconds.\n"); }[/code] The use of select 1. Czw not 0 (STDIN) 2. 1 fd which is the largest increase in value, you can use a greater scale, white waste of time [ Closed window ]