C - 套接字编程 - 我的服务器无法绑定到地址

Question

I'm writing a simple UDP echo server and for some reason the server doesn't continue executing after the bind() function. here's the code:

/*Required Headers*/


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

#define MAXLINE 100

void HandleClient(int comm_fd);
void Die (const char * msg)
{
   perror(msg);
   exit(1);
}

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

    char str[100];
    int listen_fd, comm_fd,n;
    socklen_t len;
    struct sockaddr_in servaddr, cliaddr;

    if (argc != 2) {
        fprintf(stderr, "USAGE: ./HelloITServer <port>\n");
        exit(1);
    }

    if ((listen_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        Die("Falied to create socket");
    };

    printf ("%d" ,listen_fd);
    memset( &servaddr,0, sizeof(servaddr));

    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htons(INADDR_ANY);
    servaddr.sin_port = htons(atoi(argv[1]));

    if (bind(listen_fd, (struct sockaddr *) &servaddr, sizeof(servaddr))<0)
    { 
       Die("Failed to bind socket to address");
    }
    else {
        printf ("\n binded successfully");
    }

//    if (listen(listen_fd, 10) < 0)
//    {
//          Die("Failed to listen on server socket");
//    }


    while(1) 
    {

//        if ((comm_fd = accept(listen_fd, (struct sockaddr*) NULL, NULL)) < 0) {
//              Die("Failed to accept client connection");
//          }

//        HandleClient (comm_fd);
        memset (&cliaddr,0,sizeof(cliaddr));
        len = sizeof (cliaddr);
        n = recvfrom (listen_fd,str,MAXLINE,0, (struct sockaddr *) &cliaddr,&len);

        sendto (listen_fd, str, n, 0,(struct sockaddr *) &cliaddr, len);
    }
}


void HandleClient(int comm_fd)
{

  char str[MAXLINE];
  int received;

  memset(str, 0, MAXLINE);
  received  =  read(comm_fd,str,MAXLINE);
  if (received < 0) {
      Die("Failed to receive from client");
   }
  while(received > 0)
  {

     printf("Echoing back - %s",str);

     if ( write(comm_fd, str, received) != received){
         Die("Failed to send bytes to client");
     }
    memset(str, 0, MAXLINE);
    received =   read(comm_fd,str,MAXLINE);
    if (received < 0) {
      Die("Failed to receive from client");
   }


 }       
}

it just doesn't print out the statement after executing it neither do it execute the die () function ! the client code

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include<string.h>
#include <stdlib.h>


int main(int argc,char *argv[])
{
    int sockfd,n;
    char sendline[100];
    char recvline[101];
    struct sockaddr_in servaddr;

    if (argc != 3)
    {
        fprintf(stderr, "USAGE: ./HelloClient <server_ip> <port>\n");
        exit(1);
    }

    sockfd=socket(AF_INET,SOCK_DGRAM,0);
    bzero(&servaddr,sizeof servaddr);

    servaddr.sin_family=AF_INET;
    servaddr.sin_port= htons(atoi(argv[2]));

    inet_pton(AF_INET,argv[1],&(servaddr.sin_addr));

    //connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));

//    while(1)
//    {
//        bzero( sendline, 100);
//        bzero( recvline, 100);
//        fgets(sendline,100,stdin); /*stdin = 0 , for standard input */
// 
//        write(sockfd,sendline,strlen(sendline)+1);
//        read(sockfd,recvline,100);
//        printf("%s",recvline);
//    }
    while (1) {
        bzero( sendline, 100);
        bzero( recvline, 100);
        fgets(sendline, 100, stdin);
        sendto(sockfd, sendline, strlen (sendline), 0, (const struct sockaddr *) &servaddr, (socklen_t) sizeof (servaddr));
        n = recvfrom (sockfd, recvline, 100, 0, NULL, NULL);
        printf("%d",n);
        recvline[n]=0;
        printf ("%s",recvline);
    }
}

Answer 1

Change this:

printf ("\n binded successfully");

to this:

printf ("\n binded successfully\n");

(ie, add an \\n to the end). This will cause an fflush to be performed on standard output, so that the "success" output will actually be printed to the screen, and you can see that you've entered the while-loop and are waiting for a connection.

(Alternatively, you could add an explicit fflush(stdout) after the above statement, to flush standard output yourself. But it's good practice to send the newline, and you don't seem to have a reason for not doing so.)