LINUX C网络编程学习笔记一个简单的TCP程序设计

TCP程序设计

下面的一幅图是取自《UNIX网络编程卷一》，这个简单的C/S程序的框架，应该可以一下很容易看懂。 

下面是我写的一个例子：

服务端： 

/*          tcp_server.c

*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <errno.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];
//创建sockfd描述符，AF_INET代表IPv4，SOCK_STREAM代表TCP    
    if ((sockfd = socket(AF_INET,SOCK_STREAM,0)) == -1)
    {
        fprintf(stderr,"socket error %s",strerror(errno));
        exit(1);
    }
//服务器填充sockaddr结构
    bzero(&server_addr,sizeof(struct sockaddr_in));//初始化，置0。
    server_addr.sin_family = AF_INET;
//将本机器上的long数据转化为网络上的long数据
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
//将本机的short数据转化为网络上的short数据
    server_addr.sin_port = htons(portnumber);
//捆绑sockfd描述符到IP地址
    if (bind(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr)) == -1)
    {
        fprintf(stderr,"bind error %s\n\a",strerror(errno));
        exit(1);
    }
//设置允许的最大客户端连接数
    if (listen(sockfd,5) == -1)
    {
        fprintf(stderr,"listen error %s\n\a",strerror(errno));
        exit(1);
    }
    while(1)
    {
//服务器阻塞知道客户程序建立连接
        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 %s\n\a",inet_ntoa(client_addr.sin_addr));
        if ((nbytes = read(new_fd,buffer,1024)) == -1)
        {
            fprintf(stderr,"read error %s \a\n",strerror(errno));
            exit(1);
        }
        buffer[nbytes] = '\0';
        printf("server received %s\n",buffer);
        close(new_fd);
    }
    exit(0);

} 

客户端：

/*

          tcp_client.c

*/


#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.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\a");
        exit(1);
    }
//客户端开始建立sockfd描述符
    if ((sockfd = socket(AF_INET,SOCK_STREAM,0)) == -1)
    {
        fprintf(stderr,"scoket 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;
    server_addr.sin_port = htons(portnumber);//将本机的short数据转化为网络的short数据
    server_addr.sin_addr = *((struct in_addr *)host->h_addr);
//客户程序发起连接请求
    if (connect(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr)) == -1)
    {
        fprintf(stderr,"connect error %s\a\n",strerror(errno));
        exit(1);
    }
//连接成功
    printf("Please input char:\n");
//发送数据
    fgets(buffer,1024,stdin);
    write(sockfd,buffer,strlen(buffer));
//结束通讯    
    close(sockfd);
    exit(0)}