linux C tcp/ip协议的基本过程

*****************************服务器端*********************************************
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define portnumber 3333

int main(int argc, char *argv[])
{
    int sockfd,new_fd;
    struct sockaddr_in server_addr;
    struct sockaddr_in client_addr;
    int sin_size;
    int nbytes;
    char buffer[1024];


    
    if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1) // AF_INET:IPV4;SOCK_STREAM:TCP
    {
        fprintf(stderr,"Socket error:%s\n\a",strerror(errno));
        exit(1);
    }

    
    bzero(&server_addr,sizeof(struct sockaddr_in)); // 初始化,置0
    server_addr.sin_family=AF_INET;                 // Internet
    server_addr.sin_addr.s_addr=htonl(INADDR_ANY);  // (将本机器上的long数据转化为网络上的long数据)和任
                                     何主机通信  //INADDR_ANY 表示可以接收任意IP地址的数据，即绑定到所有的IP
    //server_addr.sin_addr.s_addr=inet_addr("192.168.1.1");  //用于绑定到一个固定IP,inet_addr用于把数字加格
                                     式的ip转化为整形ip
    server_addr.sin_port=htons(portnumber);         // (将本机器上的short数据转化为网络上的short数据)端口号

    //解决问题C Bind error:Address already in use
    int opt = 1;
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) != 0){
        perror("Server setsockopt failed");
        return 1;
    }

    
    if(bind(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1)
    {
        fprintf(stderr,"Bind error:%s\n\a",strerror(errno));
        exit(1);
    }

    
    if(listen(sockfd,5)==-1)
    {
        fprintf(stderr,"Listen error:%s\n\a",strerror(errno));
        exit(1);
    }

    while(1)
    {
        
        sin_size=sizeof(struct sockaddr_in);
        if((new_fd=accept(sockfd,(struct sockaddr *)(&client_addr),&sin_size))==-1)
        {
            fprintf(stderr,"Accept error:%s\n\a",strerror(errno));
            exit(1);
        }
        fprintf(stderr,"Server get connection from %d\n",inet_ntoa(client_addr.sin_addr)); // 将网络地址转换成.字符串

        if((nbytes=read(new_fd,buffer,1024))==-1)
        {
            fprintf(stderr,"Read Error:%s\n",strerror(errno));
            exit(1);
        }
        buffer[nbytes]='\0';
        printf("Server received %s\n",buffer);

        
        close(new_fd);
        
    }

    
    close(sockfd);
    exit(0);
}


*********************客户端*****************************************
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define portnumber 3333

int main(int argc, char *argv[])
{
    int sockfd;
    char buffer[1024];
    struct sockaddr_in server_addr;
    struct hostent *host;

       
    if(argc!=2)
    {
        fprintf(stderr,"Usage:%s hostname \a\n",argv[0]);
        exit(1);
    }

    if((host=gethostbyname(argv[1]))==NULL)
    {
        fprintf(stderr,"Gethostname error\n");
        exit(1);
    }

   
    if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1) // AF_INET:Internet;SOCK_STREAM:TCP
    {
        fprintf(stderr,"Socket Error:%s\a\n",strerror(errno));
        exit(1);
    }

   
    bzero(&server_addr,sizeof(server_addr)); // 初始化,置0
    server_addr.sin_family=AF_INET;          // IPV4
    server_addr.sin_port=htons(portnumber);  // (将本机器上的short数据转化为网络上的short数据)端口号
    server_addr.sin_addr=*((struct in_addr *)host->h_addr); // IP地址
   
   
    if(connect(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1)
    {
        fprintf(stderr,"Connect Error:%s\a\n",strerror(errno));
        exit(1);
    }

   
    printf("Please input char:\n");
   
   
    fgets(buffer,1024,stdin);
    write(sockfd,buffer,strlen(buffer));

   
    close(sockfd);
    exit(0);
}