linux soket编程（tcp）

服务端

linux socket服务端编码一般包括以下六个步骤：

1. 向内核申请一个套接字，调用socket方法。
2. 绑定地址到套接字上，调用bind方法。
3. 在socket套接字上，监听并允许接入呼叫，调用listen方法。
4. 等待/接收呼叫，调用accept方法。
5. 传输数据，调用read/write等方法。
6. 关闭连接，调用close方法。

示例代码如下：

/* timeserv.c - a socket-based time of day server */#include  <stdio.h>#include  <unistd.h>#include  <sys/types.h>#include  <sys/socket.h>#include  <netinet/in.h>#include  <netdb.h>#include  <time.h>#include  <strings.h>#define   PORTNUM  13000   /* our time service phone number */#define   HOSTLEN  256#define   oops(msg)      { perror(msg) ; exit(1) ; }int main(int ac, char *av[]){struct  sockaddr_in   saddr;   /* build our address here */structhostent*hp;   /* this is part of our    */charhostname[HOSTLEN];     /* address          */intsock_id,sock_fd;       /* line id, file desc     */FILE*sock_fp;              /* use socket as stream   */char    *ctime();              /* convert secs to string */time_t  thetime;               /* the time we report     */      /*       * Step 1: ask kernel for a socket       */sock_id = socket( PF_INET, SOCK_STREAM, 0 );    /* get a socket */if ( sock_id == -1 ) oops( "socket" );      /*       * Step 2: bind address to socket.  Address is host,port       */bzero( (void *)&saddr, sizeof(saddr) ); /* clear out struct     */gethostname( hostname, HOSTLEN );       /* where am I ?         */hp = gethostbyname( hostname );         /* get info about host  */                                        /* fill in host part    */bcopy( (void *)hp->h_addr, (void *)&saddr.sin_addr, hp->h_length);saddr.sin_port = htons(PORTNUM);        /* fill in socket port  */saddr.sin_family = AF_INET ;            /* fill in addr family  */if ( bind(sock_id, (struct sockaddr *)&saddr, sizeof(saddr)) != 0 )       oops( "bind" );      /*       * Step 3: allow incoming calls with Qsize=1 on socket       */if ( listen(sock_id, 1) != 0 ) oops( "listen" );      /*       * main loop: accept(), write(), close()       */while ( 1 ){       sock_fd = accept(sock_id, NULL, NULL); /* wait for call */printf("Wow! got a call!\n");       if ( sock_fd == -1 )       oops( "accept" );       /* error getting calls  */       sock_fp = fdopen(sock_fd,"w");  /* we'll write to the   */       if ( sock_fp == NULL )          /* socket as a stream   */       oops( "fdopen" );       /* unless we can't      */       thetime = time(NULL);           /* get time             */       /* and convert to strng */       fprintf( sock_fp, "The time here is .." );       fprintf( sock_fp, "%s", ctime(&thetime) );        fclose( sock_fp );              /* release connection   */}}

客户端

socket客户端一般分为四个步骤：

向内核请求建立socket。调用socket。

与服务器相连。调用connect。

传送数据。调用read，write等方法。

挂断。调用close。

示例代码如下：

/* timeclnt.c - a client for timeserv.c *              usage: timeclnt hostname portnumber */#include       <stdio.h>#include       <sys/types.h>#include       <sys/socket.h>#include       <netinet/in.h>#include       <netdb.h>#define        oops(msg)       { perror(msg); exit(1); }main(int ac, char *av[]){struct sockaddr_in  servadd;        /* the number to call */struct hostent      *hp;            /* used to get number */int    sock_id, sock_fd;            /* the socket and fd  */char   message[BUFSIZ];             /* to receive message */int    messlen;                     /* for message length */     /*      * Step 1: Get a socket      */sock_id = socket( AF_INET, SOCK_STREAM, 0 );    /* get a line   */if ( sock_id == -1 ) oops( "socket" );          /* or fail      */     /*      * Step 2: connect to server      *         need to build address (host,port) of server  first      */bzero( &servadd, sizeof( servadd ) );   /* zero the address     */hp = gethostbyname( av[1] );            /* lookup host's ip #   */if (hp == NULL) oops(av[1]);            /* or die               */bcopy(hp->h_addr, (struct sockaddr *)&servadd.sin_addr, hp->h_length);servadd.sin_port = htons(atoi(av[2]));  /* fill in port number  */servadd.sin_family = AF_INET ;          /* fill in socket type  */       /* now dial     */if ( connect(sock_id,(struct sockaddr *)&servadd, sizeof(servadd)) !=0)       oops( "connect" );     /*      * Step 3: transfer data from server, then hangup      */messlen = read(sock_id, message, BUFSIZ);     /* read stuff   */if ( messlen == - 1 )       oops("read") ;if ( write( 1, message, messlen ) != messlen )  /* and write to */       oops( "write" );                        /* stdout       */close( sock_id );    }