linux socket小例

/*
socket select模型，服务端
绝大多数注释自己写的，参考man
*/
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/un.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <netinet/in.h>
#define SERVPORT 3333
#define BACKLOG 10
#define MAX_CONNECTED_NO 10
#define MAXDATASIZE 100
int main()
{
/*
struct sockaddr_in {
//地址族AF_INET（IPv4）AF_INET6（IPv6）AF_LOCAL（UNIX域协议）AF_LINK（链路地址协议）AF_KEY（密钥套接字socket）AF_APPLETALK（ddp）
　　 short int sin_family;
//端口号
　　 unsigned short int sin_port;
*
* struct in_addr {
* unsigned long s_addr;
* }
*
//地址
struct in_addr sin_addr;
unsigned char sin_zero[8];
}
eg:
struct sockaddr_in ina;
bzero(&ina,sizeof(ina));
ina.sin_family=AF_INET;
ina.sin_port=htons(23);
ina.sin_addr.s_addr = inet_addr("132.241.5.10");
AF_INET和PF_INET略有差异
*/
struct sockaddr_in server_sockaddr,client_sockaddr;
int sin_size,recvbytes;
fd_set readfd;
fd_set writefd;
int sockfd,client_fd;
char buf[MAXDATASIZE];
/*
int socket(int domain, int type, int protocol);
domain:PF_INET...
type:SOCK_STREAM,SOCK_STREAM,SOCK_RAW...
protocol:/etc/protocols tcp,udp...
*/
if((sockfd = socket(AF_INET,SOCK_STREAM,0))==-1){
perror("socket");
exit(1);
}
printf("socket success!,sockfd=%d\n",sockfd);
server_sockaddr.sin_family=AF_INET;
server_sockaddr.sin_port=htons(SERVPORT);
server_sockaddr.sin_addr.s_addr=INADDR_ANY;
//set to 0
bzero(&(server_sockaddr.sin_zero),8);
/*
int bind(int sockfd, const struct sockaddr *my_addr,socklen_t addrlen);
sockfd:created by socket
*my_addr:convert from sockaddr_in
addrlen:sizeof(sockaddr)
*/
if(bind(sockfd,(