Why does this server not outputting anything?

Question

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

int main()
{

int sock, newsock;
    struct sockaddr server_name = {AF_UNIX, "Fred"};
    socklen_t len=sizeof(struct sockaddr)+5;

    if( (sock=socket(AF_UNIX,SOCK_STREAM,0)) ==-1)
    {
        printf("error creating socket");
        return -1;
    }

    if( bind(sock,&server_name,len) != 0 ) //binding
    {

        printf("socket bind error ");
        return -1;
    }


   if(listen(sock,10)!=0)  //set sock to listen
   {
        printf("error listening");
        return -1;
   }

    printf("Waiting for connections....");

   while(1)
   {
        newsock=accept(sock, (struct sockaddr*)NULL, NULL);

        char temp[1000]="gggggg\n";
        write(newsock,temp,strlen(temp));

        write(newsock,temp,strlen(temp));
        close(newsock);

        sleep(1);

   }

return 0;
}

"Waiting for connections..." doesn't appear on my screen. What's the problem? I tried print function everywhere. Nothing shows up..What is the problem? I don't see that I closed stdout..Can anyone help? Thank you.

Answer 1

The standard output is line buffered by default. Your program outputs something without the new line and then enters the loop. You need to add a new line like this:

printf("Waiting for connections....\n");

For similar reasons, the error messages should be output to standard error, because it's not buffered.

fprintf(stderr, "error creating socket\n");

Answer 2

Firstly, you should add '\n' add the end of log:"Waiting for connections....\n", then the log cann't be buffered, and be outputted.

Secondly, your program is error, the correct program is like this:

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

int main()
{

    int sock, newsock;
    struct sockaddr_un server_name;
    socklen_t len= sizeof(server_name);
    unlink("Fred");
    if( (sock=socket(AF_UNIX,SOCK_STREAM,0)) ==-1)
    {
        printf("error creating socket\n");
        return -1;
    }

    server_name.sun_family = AF_UNIX;
    strcpy(server_name.sun_path, "Fred");

    if( bind(sock,(struct sockaddr*)&server_name,len) != 0 ) //binding
    {

        printf("socket bind error \n");
        return -1;
    }


   if(listen(sock,10)!=0)  //set sock to listen
   {
        printf("error listening\n");
        return -1;
   }

   printf("Waiting for connections....\n");

   while(1)
   {
        newsock=accept(sock, (struct sockaddr*)NULL, NULL);

        char temp[1000]="gggggg\n";
        write(newsock,temp,strlen(temp));

        write(newsock,temp,strlen(temp));
        close(newsock);

        sleep(1);

   }

return 0;
}