c - 套接字编程

Question

我有一个简单的服务器和一个客户端。我在我机器的某个端口上运行服务器，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它无法连接到服务器。请查看以下文件:

服务器.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;
}

客户端.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，确保将相同的端口号传递给服务器和客户端。如果端口号不同，服务器和客户端之间的通信将不会发生。

这是本地机器的代码。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;
}

希望对你有帮助