Summary of Select () function usage and question point __ function

1. function prototype and header file-Windows Bottom file is
#include <WinSock2.h>

-Linux bottom file for #include <unistd.h>
#include <sys/time.h>

-prototype int Select (int nfds,fd_set *readsets,fd_set *writesets,fd_set *exceptsets,const struct timeval)

Return value: Number of Ready descriptor, timeout return 0, error return-1

2, the measured code should pay attention to the point is: each time the select end of the descriptor value will change, so each cycle start to clean the Read_fds and Write_fds, and then the Socketid Fdset again.
The server-side code is as follows

#include <stdio.h> #include <string> #include <vector> #ifdef WINDOWS #include <WinSock2.h> # pragma comment (lib, "Ws2_32.lib") #endif #ifdef LINUX #include <unistd.h> #include <stdio.h> #include < stdlib.h> #include <errno.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/ in.h> #endif #pragma warning (disable:4996) #define Default_port 48000 #define MaxLen 4096 void prepareids (int listen_f d,std::vector<int> accept_fd,int &max_fd,fd_set &read_fds,fd_set &write_fds) {FD_ZERO (&read_
	FDS);
	Fd_zero (&write_fds);
	Fd_set (LISTEN_FD, &read_fds);
	MAX_FD = LISTEN_FD;
		for (Auto Itor = Accept_fd.begin (); Itor!= accept_fd.end (); itor++) {Fd_set (*itor, &read_fds);
		Fd_set (*itor, &write_fds);
	MAX_FD = Max (MAX_FD, *itor);
} MAX_FD = 1;
	} void doreadactions (int fd) {char buff[4096];
	memset (buff, 0, sizeof (buff));
	int len = recv (fd, Buff, maxlen, 0); printf ("Receive buffer[%s]\n ", buff);
	} void dowriteactions (int fd) {Char *buff = ' This is the ' message sending from HOST. '
	Send (FD, buff, strlen (buff) +1, 0);
printf ("Host Send Message ok\n");
	int main () {int listen_fd;
	struct sockaddr_in servaddr;
	Fd_set Readfds, Writefds;
	Std::vector<int> Accept_fds;
	int max_fd;
	Timeval timeout;
	Timeout.tv_sec = 3;
	Timeout.tv_usec = 500000;
	Fd_zero (&readfds);
	Fd_zero (&writefds);

	Wsadata InitData;
		if (WSAStartup (Makeword (2, 2), &initdata)) {printf ("Can not init socket");
	return-1; if (LISTEN_FD = socket (af_inet, sock_stream, ipproto_tcp) = =-1) {printf ("Create Socket Error:%s (errno:%d) \ n", s
		Trerror (errno), errno);
	Exit (0);
	} memset (&servaddr, 0, sizeof (SERVADDR));
	servaddr.sin_family = af_inet;
	SERVADDR.SIN_ADDR.S_ADDR = htonl (Inaddr_any);
	Servaddr.sin_port = htons (Default_port); if (Bind (LISTEN_FD, (struct sockaddr*) &servaddr,sizeof (servaddr)) = = 1) {printf (Bind socket Error:%s (errno:%d) \ n ", strError (errno), errno);
		Closesocket (LISTEN_FD);
	Exit (0);
		} if (listen (listen_fd) = = 1) {printf ("Listen socket Error:%s (errno:%d) \ n", Strerror (errno), errno);
		Closesocket (LISTEN_FD);
	Exit (0);
	} accept_fds.clear ();
		while (1) {prepareids (listen_fd, Accept_fds, MAX_FD, Readfds, Writefds);
		printf ("r1:readfds.fd_count[%d],writefds.fd_count[%d]\n", Readfds.fd_count, Writefds.fd_count);
		int RTN = SELECT (MAX_FD, &readfds, &writefds, 0, &timeout);
		printf ("r2:readfds.fd_count[%d],writefds.fd_count[%d]\n", Readfds.fd_count, Writefds.fd_count); if (Fd_isset (LISTEN_FD, &readfds))//If LISTEN_FD has a value, represents a new link, stored in the new Socketid {int new_socket = accept (LISTEN_FD, Stru
			CT sockaddr*) null,null);
			printf ("Receive client accept\n");
				if (new_socket<0) {printf ("Accept socket Error:%s (errno:%d)", Strerror (errno), errno);
			Continue
		} accept_fds.push_back (New_socket); for (Auto Itor = Accept_fds.begin (); Itor!= accept_fds.end (); itor++) {if (Fd_isset (*itor, &readfds)) doreadactions (*itor);			
		if (Fd_isset (*itor, &writefds)) dowriteactions (*itor);
} return 0; }

The client code is as follows:

#include <Winsock2.h>
#include <stdio.h>
#pragma comment (lib, "Ws2_32.lib") 
#pragma message ("Error!!!")
#define DEFAULTPORT 48000

void Main ()
{
	WORD wversionrequested;
	Wsadata Wsadata;
	int err;
	
	wversionrequested = Makeword (2, 2);
	
	Err = WSAStartup (wversionrequested, &wsadata);
	if (Err!= 0) {return
		;
	}
	
	SOCKET Sockclient=socket (af_inet,sock_stream,0);

	Sockaddr_in addrsrv;
	Addrsrv.sin_addr. S_un. S_ADDR=INET_ADDR ("127.0.0.1");
	addrsrv.sin_family=af_inet;
	Addrsrv.sin_port=htons (defaultport);
	Connect (sockclient, (sockaddr*) &addrsrv,sizeof (sockaddr));


	Send (Sockclient, "This are Test", strlen ("This is Test") +1,0);
	Char recvbuf[100];
	memset (recvbuf,0,sizeof (RECVBUF));
	while (recv (sockclient,recvbuf,100,0) >0)
	{
		printf ("%s\n", recvbuf);
	}
	Recv (sockclient,recvbuf,100,0);
	printf ("%s\n", recvbuf);
	Closesocket (sockclient);
	WSACleanup ();
	
}