套接字编程

Question

我有一个简单的服务器和客户端。我在我的机器的某个端口运行服务器，当我尝试将我的客户端连接到服务器时，它说网络无法访问。有人可以建议我为什么无法连接到服务器。请看看下面的文件：

server.c

#include <stdlib.h> 
#include <sys/types.h> 
#include <sys/socket.h> 
#include <errno.h> 
#include <stdio.h> 
#include <string.h> 
#include <unistd.h> 
#include <netinet/in.h> 

void error(const char *msg) 
{ 
    perror(msg); 
    exit(1); 
} 

int main(int argc, char *argv[]){ 

    int sockfd, newsockfd, portno; 
    struct sockaddr_in serv_addr; 
    char sendmessage[50]; 

    if(argc != 2){ 
     fprintf(stderr, "ERROR, Port number not provided or Command line argument is not 2\n"); 
     exit(1); 
    } 

    //creating a socket for the server 
    sockfd = socket(AF_INET, SOCK_STREAM, 0); 
    if(sockfd < 0){ 
     error("ERROR opening socket"); 
    } 

    portno = atoi(argv[1]); 

    //describing the attributes for socket address 
    serv_addr.sin_family = AF_INET; 
    serv_addr.sin_addr.s_addr = INADDR_ANY; 
    serv_addr.sin_port = htons(portno); 

    if(bind(sockfd, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) < 0){ 
     error("Error on binding the socket"); 
     exit(1); 
    } 

    //allowing only 1 client to connect to the server at a time 
    if(listen(sockfd, 1) < 0){ 
     error("Error in listening to the socket"); 
    } 

    printf("Server is running...... \nWaiting for the connection from the client on port: %d\n", portno); 

    while(1){ 
     //accepts the connection from the client 
     newsockfd = accept(sockfd, (struct sockaddr*)NULL, NULL); 

     if(newsockfd < 0){ 
      error("Error on accepting"); 
     } 

     strcpy(sendmessage, "Welcome to The Server"); 
     write(newsockfd, sendmessage, strlen(sendmessage)); 
    } 
    return 0; 
} 

client.c

#include <stdlib.h> 
#include <unistd.h> 
#include <stdio.h> 
#include <string.h> 
#include <errno.h> 
#include <sys/socket.h> 
#include <sys/types.h> 
#include <netinet/in.h> 

void error(const char *msg) 
{ 
    perror(msg); 
    exit(0); 
} 

int main(int argc, char* argv[]){ 

    int sockfd; 
    char recvmessage[100]; 
    char sendmessage[100]; 
    int portno; 
    struct hostent *server; 

    struct sockaddr_in serv_addr; 

    if(argc != 3){ 
     fprintf(stderr, "Error, either IP address or port number not provided.\n"); 
     exit(1); 
    } 

    portno = atoi(argv[2]); 

    sockfd = socket(AF_INET, SOCK_STREAM, 0); 

    if(socket < 0){ 
     error("Error with creating a socket"); 
    } 

    //check whether the host exist or not 
    server = gethostbyname(argv[1]); 

    if(server == NULL){ 
     fprintf(stderr, "ERROR, the host is not defined\n"); 
     exit(0); 
    } 

    //creating the socket 
    serv_addr.sin_family = AF_INET; 
    serv_addr.sin_port = htons(portno); 
    serv_addr.sin_addr.s_addr = inet_addr(argv[1]); 

    //connecting the client to the socket 
    if(connect(sockfd, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) < 0){ 
     error("Could not connect to the server......"); 
     exit(1); 
    } 

    printf("Connection Successful to the Server\n"); 
    return 0; 
} 

Answer 1

首先确保你通过相同的端口号到两个服务器&客户端。如果端口号不同，则不会发生服务器和客户端之间的通信。

这里是本地机器的代码。您可以稍微更改代码并传递IP地址。

Server.c

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <unistd.h> 
#include <arpa/inet.h> 
#include <sys/types.h> 
#include <netinet/in.h> 
#include <sys/socket.h> 

#define PORTNUM 2348 

#define bufferLength 500 


int main(int argc, char *argv[]) 
{ 

    char buffer[bufferLength]; 

    struct sockaddr_in dest; /* socket info about the machine connecting to us */ 
    struct sockaddr_in serv; /* socket info about our server */ 
    int mysocket;   /* socket used to listen for incoming connections */ 
    socklen_t socksize = sizeof(struct sockaddr_in); 

    memset(&serv, 0, sizeof(serv));   /* zero the struct before filling the fields */ 
    serv.sin_family = AF_INET;    /* set the type of connection to TCP/IP */ 
    serv.sin_addr.s_addr = htonl(INADDR_ANY); /* set our address to any interface */ 
    serv.sin_port = htons(PORTNUM);   /* set the server port number */  

    mysocket = socket(AF_INET, SOCK_STREAM, 0); 

    /* bind serv information to mysocket */ 
    bind(mysocket, (struct sockaddr *)&serv, sizeof(struct sockaddr)); 

    /* start listening, allowing a queue of up to 1 pending connection */ 
    listen(mysocket, 1); 


    int consocket; 

    int cpid; 

    while(1) 
    { 

      consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize); 

      perror("consocket\n"); 

      if((cpid = fork()) == 0) 
      { 
      printf("inside child process\n\n\n"); 

      close(mysocket); 

      close(consocket); 

      int recivedBytes = recv(consocket, buffer, bufferLength, 0); 

      buffer[recivedBytes] = '\0'; 

      printf("recieved data %s \n", buffer); 

      return 0; 
      } 
      else 
      close(consocket); 

    } 

    close(mysocket); 

    return EXIT_SUCCESS; 
} 

Client.c

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <unistd.h> 
#include <arpa/inet.h> 
#include <sys/types.h> 
#include <netinet/in.h> 
#include <sys/socket.h> 
#define MAXRCVLEN 500 

#define PORTNUM 2348 


int main(int argc, char *argv[]) 
{ 
    char buffer[] = "My name is khan"; /* +1 so we can add null terminator */ 
    int len, mysocket; 
    struct sockaddr_in dest; 


    mysocket = socket(AF_INET, SOCK_STREAM, 0); 

    memset(&dest, 0, sizeof(dest));    /* zero the struct */ 
    dest.sin_family = AF_INET; 
    dest.sin_addr.s_addr = inet_addr("127.0.0.1"); /* set destination IP number */ 
    dest.sin_port = htons(PORTNUM);    /* set destination port number */ 

    connect(mysocket, (struct sockaddr *)&dest, sizeof(struct sockaddr)); 

    len = send(mysocket, buffer, strlen(buffer), 0); 
    perror("len\n"); 

    /* We have to null terminate the received data ourselves */ 
    buffer[len] = '\0'; 

    printf("sent %s (%d bytes).\n", buffer, len); 

    close(mysocket); 
    return EXIT_SUCCESS; 
} 

希望这有助于