socket客户端

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创建一个套接字socket()系统调用。yiibai
套接字连接的服务器地址使用connect()系统调用。
发送和接收数据。做到这一点的方法有许多，但最简单的方法是使用read() 和write() 系统调用。

现在要把上面这些步骤的形式写成源代码。把这个代码写client.c文件并用gcc编译器编译。

运行该程序，并通过服务器的主机名和端口号连接到服务器，必须已经运行在另一个UNIX窗口。

#include <stdio.h>#include <sys/types.h> #include <sys/socket.h>#include <netinet/in.h>int main(int argc, char *argv[]){    int sockfd, portno, n;    struct sockaddr_in serv_addr;    struct hostent *server;    char buffer[256];    if (argc < 3) {        fprintf(stderr,"usage %s hostname port\n", argv[0]);        exit(0);    }    portno = atoi(argv[2]);    /* Create a socket point */    sockfd = socket(AF_INET, SOCK_STREAM, 0);    if (sockfd < 0)     {        perror("ERROR opening socket");        exit(1);    }    server = gethostbyname(argv[1]);    if (server == NULL) {        fprintf(stderr,"ERROR, no such host\n");        exit(0);    }    bzero((char *) &serv_addr, sizeof(serv_addr));    serv_addr.sin_family = AF_INET;    bcopy((char *)server->h_addr,            (char *)&serv_addr.sin_addr.s_addr,                server->h_length);    serv_addr.sin_port = htons(portno);    /* Now connect to the server */    if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0)     {         perror("ERROR connecting");         exit(1);    }    /* Now ask for a message from the user, this message    * will be read by server    */    printf("Please enter the message: ");    bzero(buffer,256);    fgets(buffer,255,stdin);    /* Send message to the server - by yiibai.com */    n = write(sockfd,buffer,strlen(buffer));    if (n < 0)     {         perror("ERROR writing to socket");         exit(1);    }    /* Now read server response */    bzero(buffer,256);    n = read(sockfd,buffer,255);    if (n < 0)     {         perror("ERROR reading from socket");         exit(1);    }    printf("%s\n",buffer);    return 0;}

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