select read write

转载：http://blog.csdn.net/beginning1126/article/details/8057498

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1. 服务器 当有新连接来的时候,通过在select上轮循写的fd(文件描述符)发送一句欢迎词。然后每次受到客户端的数据后,把接受到的数据返回给客户端。演示了在select上轮循写的操作。对于监视读操作,只有当数据来的时候,读操作的fd才会返回.而对于写的操作fd,则是轮询。

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/*
the example is writed by minrongf,date: 20090214
#filename: selectsvr.c
* */
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/time.h>
typedef int SOCKET;
#define MAXBUFSIZE 1024
#define NLISTEN 1024
#define isvalidsock(s) ( ( s ) > 0 )
void set_address( char *hname, char *sname,struct sockaddr_in *sap, char *protocol )
{
struct servent *sp;
struct hostent *hp;
char *endptr;
short port;
bzero( sap, sizeof( *sap ) );
sap->sin_family = AF_INET;
if ( hname != NULL )
{
if ( !inet_aton( hname, &sap->sin_addr ) )
{
hp = gethostbyname( hname );
if ( hp == NULL )
error( 1, 0, "unknown host: %s/n", hname );
sap->sin_addr = *( struct in_addr * )hp->h_addr;
}
}
else
sap->sin_addr.s_addr = htonl( INADDR_ANY );
port = strtol( sname, &endptr, 0 );
if ( *endptr == '/0' )
sap->sin_port = htons( port );
else
{
sp = getservbyname( sname, protocol );
if ( sp == NULL )
error( 1, 0, "unknown service: %s/n", sname );
sap->sin_port = sp->s_port;
}
}
SOCKET tcp_server( char *hname, char *sname )
{
struct sockaddr_in local;
SOCKET s;
const int on = 1;
set_address( hname, sname, &local, "tcp" );
s = socket( AF_INET, SOCK_STREAM, 0 );
if ( !isvalidsock( s ) )
error( 1, errno, "socket call failed" );
if ( setsockopt( s, SOL_SOCKET, SO_REUSEADDR,
( char * )&on, sizeof( on ) ) )
error( 1, errno, "setsockopt failed" );
if ( bind( s, ( struct sockaddr * ) &local,
sizeof( local ) ) )
error( 1, errno, "bind failed" );
if ( listen( s, NLISTEN ) )
error( 1, errno, "listen failed" );
return s;
}
int main(int argc,char**argv)
{
int i,maxi,maxfd,listenfd,connfd,sockfd;
int nready,client[FD_SETSIZE];
fd_set rset,alllset,wset,wsetsave;
char buf[MAXBUFSIZE];
socklen_t clilen;
struct sockaddr_in servaddr,cliaddr;
int rval;
struct timeval to;
int n = 0;
listenfd = tcp_server(NULL,"5000");
FD_ZERO(&alllset);
FD_ZERO(&wsetsave);
FD_SET(listenfd,&alllset);
maxfd = listenfd;
for(i = 0; i < FD_SETSIZE;i++)
client[i] = -1;
maxi = -1;
while(1)
{
FD_ZERO(&rset);
rset = alllset;
wset = wsetsave;
printf("server waiting...,maxfd:%d/n",maxfd);
nready = select(maxfd+1,&rset,&wset,NULL,NULL);
if(FD_ISSET(listenfd,&rset))
{
clilen = sizeof(cliaddr);
connfd = accept(listenfd,(struct sockaddr*)&cliaddr,&clilen);
for(i = 0; i< FD_SETSIZE; i++)
{
if(client[i] < 0)
{
client[i] = connfd;
break;
}
}
if(i == FD_SETSIZE)
{
printf("too many clients /n");
exit(1);
}
FD_SET(connfd,&alllset);
FD_SET(connfd,&wsetsave);
printf("addinng client on fd %d/n",connfd);
if(connfd > maxfd)
maxfd = connfd;
if( i > maxi)
maxi = i;
if(--nready <= 0)
continue;
}
for(i = 0; i <= maxi; i++)
{
if((sockfd = client[i]) < 0 )
continue;
if(FD_ISSET(sockfd,&rset))
{
bzero(buf,100);
if((n = recv(sockfd,buf,MAXBUFSIZE,0)) <= 0)
{
close(sockfd);
FD_CLR(sockfd,&alllset);
client[i] = -1;
printf("recv error,client:%d exit/n",sockfd);
}
else
{
sleep(2);
printf("serving client read on fd %d,recv datalen: %d,data:%s /n",sockfd,n,buf);
write(sockfd,buf,n);
}
if(--nready <= 0 )
break;
}
else if(FD_ISSET(sockfd,&wset))
{
char buf1[100] = {""};
sprintf(buf1,"Welcome the selectsvr .../n");
if((n = send(sockfd,buf1,strlen(buf1),0)) <= 0)
{
close(sockfd);
FD_CLR(sockfd,&wsetsave);
printf("send error,client:%d exit/n",sockfd);
}
else
{
FD_CLR(sockfd,&wsetsave);
printf("serving client write on fd %d,data:%s/n",sockfd,buf1);
}
sleep(5);
}
}
}
}

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通过: gcc selectsvr.c -o selectsvr 编译得到执行文件selectsvr

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2. 客户端

[cpp] view plaincopy

/*
the example is writed by minrongf,date: 20090214
#filename:selectcli.c
* */
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/time.h>
typedef int SOCKET;
#define MAXBUFSIZE 1024
#define NLISTEN 1024
#define isvalidsock(s) ( ( s ) > 0 )
void set_address( char *hname, char *sname,struct sockaddr_in *sap, char *protocol )
{
struct servent *sp;
struct hostent *hp;
char *endptr;
short port;
bzero( sap, sizeof( *sap ) );
sap->sin_family = AF_INET;
if ( hname != NULL )
{
if ( !inet_aton( hname, &sap->sin_addr ) )
{
hp = gethostbyname( hname );
if ( hp == NULL )
error( 1, 0, "unknown host: %s/n", hname );
sap->sin_addr = *( struct in_addr * )hp->h_addr;
}
}
else
sap->sin_addr.s_addr = htonl( INADDR_ANY );
port = strtol( sname, &endptr, 0 );
if ( *endptr == '/0' )
sap->sin_port = htons( port );
else
{
sp = getservbyname( sname, protocol );
if ( sp == NULL )
error( 1, 0, "unknown service: %s/n", sname );
sap->sin_port = sp->s_port;
}
}
/* tcp_client - set up for a TCP client */
SOCKET tcp_client( char *hname, char *sname )
{
struct sockaddr_in peer;
SOCKET s;
set_address( hname, sname, &peer, "tcp" );
s = socket( AF_INET, SOCK_STREAM, 0 );
if ( !isvalidsock( s ) )
error( 1, errno, "socket call failed" );
if ( connect( s, ( struct sockaddr * )&peer,
sizeof( peer ) ) )
error( 1, errno, "connect failed" );
return s;
}
int main(int argc,char**argv)
{
SOCKET s;
s = tcp_client(NULL,"5000");
char buf[100] = {""};
recv(s,buf,100,0);
printf("%s/n",buf);
printf("please input data(quit exit):");
while(fgets(buf,100,stdin) != NULL)
{
if(strcmp(buf,"quit") == 0)
break;
send(s,buf,strlen(buf),0);
recv(s,buf,100,0);
printf("echo data:%s/n",buf);
printf("please input data(quit exit):");
}
}

通过: gcc selectcli.c -o selectcli 得到客户端执行程序.

在上面的测试例子中,程序只是简单演示了如何使用select来轮询可读、可写操作的。

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