Socket 下TCP通信学习笔记

由于公司需要开发底层套接字通信，所以把大一的C重新拾回来学习，但是就学校的那点皮毛远远达不到公司项目的要求，一切重来，学习Linux下的C编程。
以Linux下TCP socket通信为实例。
在Socket通信中，服务器端分为socket初始化、绑定、监听、接受连接、发送接收数据五个过程，客户端分为socket初始化、连接服务器socket、发送接收数据三个过程。如图所示。

作为初学者，socket套接字学习的关键点在于那几个函数的学习和理解。
代码先上，解析在注释中：
说明：本代码已经加入多线程问题，请查阅时注意。Linux下GCC编译通过。

server.c：

/* 
 * server.c 
 * 
 *  Created on: 2011-3-13 
 *      Author: n2 
 */  
  
#include <pthread.h>  
#include <stdio.h>  
#include <stdlib.h>  
#include <string.h>  
#include <unistd.h>  
#include <sys/types.h>   
#include <sys/socket.h>  
#include <netinet/in.h>  
  
#define PORTL 8742  
  
pthread_t th1,th2;  
//声明读写函数  
void *recv_info(int newsockfd);  
void *send_info(int newsockfd);  
//输出错误提示  
void error(const char *msg)  
{  
    perror(msg);  
    exit(1);  
}  
  
int main(int argc, char *argv[])  
{  
     int sockfd, newsockfd;  
     unsigned int clilen;  
     struct sockaddr_in serv_addr, cli_addr;//socket通信中Internet地址变量定义  
  
     sockfd = socket(AF_INET, SOCK_STREAM, 0);//初始化socket  
     if (sockfd < 0)  
        error("ERROR opening socket");  
     bzero((char *) &serv_addr, sizeof(serv_addr));//地址变量进行清零  
  
     serv_addr.sin_family = AF_INET;  
     serv_addr.sin_addr.s_addr = INADDR_ANY;  
     serv_addr.sin_port = htons(PORTL);//地址变量添加协议簇、监听地址、端口  
     if (bind(sockfd, (struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)//绑定socket  
              error("ERROR on binding");  
     listen(sockfd,10);  
  
     clilen = sizeof(cli_addr);  
       
     while(1){  
         newsockfd = accept(sockfd,(struct sockaddr *) &cli_addr,&clilen);//阻塞等待连接  
  
         //连接成功，创建读写线程  
         memset(&th1, 0, sizeof(th1));  
         memset(&th2, 0, sizeof(th2));  
         int thr1 = pthread_create(&th1,NULL,recv_info,newsockfd);  
         if(thr1!=0)  
             printf("recv Creation failed!/n");  
         int thr2 = pthread_create(&th2,NULL,send_info,newsockfd);  
         if(thr2!=0)  
             printf("send Creation failed!/n");  
     }  
     //等待线程结束  
    pthread_join(th1,NULL);  
    pthread_join(th2,NULL);  
  
    close(sockfd);  
    return 0;  
}  
  
//读取来自于客户端的数据并显示  
void *recv_info(int newsockfd)  
{  
        int n;  
        char buffer[512];  
  
        if (newsockfd < 0)  
            pthread_exit((void *)1);  
        else  
        {  
            while(1)  
            {  
                bzero(buffer,512);  
                n = recv(newsockfd,buffer,sizeof(buffer),0);  
                printf("From client: %s/n",buffer);  
                if (n < 0)  
                    pthread_exit(NULL);  
                else  
                    //当读取数据为'0'时关闭读取线程  
                    if(buffer[0]=='0')  
                        pthread_exit(NULL);  
            }  
        }  
}  
//向客户端发送数据  
void *send_info(int newsockfd)  
{  
        int n;  
        char buffer[256];  
        bzero(buffer,256);  
        while(1)  
        {  
            if(newsockfd<0)  
                error("ERROR on accept");  
            gets(buffer);  
            n =send(newsockfd,buffer,sizeof(buffer),0);  
            if (n < 0)  
                error("ERROR writing to socket");  
            if(buffer[0]=='0')  
                //当发送数据为'0'时关闭发送线程  
                pthread_exit((NULL);  
        }  
}  

client.c

/* 
 * client.c 
 * 
 *  Created on: 2011-3-13 
 *      Author: n2 
 */  
 
#include   <pthread.h>  
#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>  
#include   <unistd.h>  
 
#define PORTL 8742  
pthread_t th1,th2;  
  
void *send_info(int saiCId);  
void *read_info(int saiCId);  
  
int main()  
{  
    struct sockaddr_in saiClient;  
    int saiCId , connectId ;  
  
    char * host_name="192.168.1.233";//服务器端IP地址  
    struct hostent *server_host_name;  
    server_host_name = gethostbyname(host_name);  
  
  
    saiClient.sin_family = AF_INET;  
    saiClient.sin_port = htons(PORTL);  
    saiClient.sin_addr.s_addr= ((struct in_addr *)(server_host_name->h_addr))->s_addr;//转义字符串格式的IP地址  
  
    saiCId = socket(AF_INET,SOCK_STREAM,0);  
  
     memset(&th1, 0, sizeof(th1));  
     memset(&th2, 0, sizeof(th2));  
  
  
     connectId = connect(saiCId,(struct sockaddr *)(&saiClient),sizeof(struct sockaddr_in));  
     if(connectId<0)  
         printf("connect failed!");  
  
     int thr1 = pthread_create(&th1,NULL,send_info,saiCId);  
     if(thr1!=0)  
         printf(" Send Thread Creation failed!/n");  
  
     int thr2 = pthread_create(&th2,NULL,read_info,saiCId);  
     if(thr2!=0)  
         printf(" Send Thread Creation failed!/n");  
  
    pthread_join(th1,NULL);  
    pthread_join(th2,NULL);  
  
    close(saiCId);  
}  
  
void *send_info(int saiCId)  
{  
    int n;  
    char buffer[256];  
    while (1)  
    {  
        bzero(buffer, 256);  
        gets(buffer);  
  
        n = send(saiCId, buffer, sizeof(buffer), 0);  
        if (n < 0)  
            error("ERROR writing to socket");  
        if (buffer[0] == '0')  
            return NULL;  
    }  
}  
  
void *read_info(int saiCId)  
{  
        int n;  
        char buffer[512];  
  
        if (saiCId < 0)  
            pthread_exit((void *)1);  
        while(1)  
        {  
                bzero(buffer,512);  
                n = recv(saiCId,buffer,sizeof(buffer),0);  
                printf("From server:  %s/n", buffer);  
                if (n < 0)  
                    pthread_exit((void *)1);  
                else  
                    if(buffer[0]=='0')  
                        return NULL;  
        }  
  
}