title: error " undefined reference to " at compile time
body: <p>when I compile this file it keeps giving me </p>
  
  <pre><code>Undefined reference to size
  Undefined reference to file
  </code></pre>
  
  <p>I compiled it twice in the second time it give me both error, when the first time it give me only the second error.</p>
  
  <p>can I know exactly what is the problem and how I can solve it?  </p>
  
  <p>ps: i use <code>gcc -o ser server.c</code> to compile  </p>
  
  <p>Sorry I had problem with my Net</p>
  
  <pre class="lang-c prettyprint-override"><code> #include&lt;stdio.h&gt;
   #include&lt;errno.h&gt;
   #include&lt;arpa/inet.h&gt;
   #include&lt;string.h&gt;
   #include&lt;netinet/in.h&gt;
   #include&lt;sys/types.h&gt;
   #include&lt;sys/socket.h&gt;
   #include&lt;stdlib.h&gt;
   #include&lt;fcntl.h&gt;
  
  #define Max_len 1049
  void error (char * str)
  {
  perror(str);
  exit(0);
  }
  </code></pre>
  
  <p>this the complete code</p>
  
  <pre><code>int main (int argc, char ** arg)
   {
        //------------------------- define data type
   int listenfd,connfd,clilen,portno,fil_fd;
   char buff[Max_len], *str,f_name[100],car=0xAA;
   struct sockaddr_in servaddr,cliaddr;
   FILE * file_ptr;         //to store the pointer that point to the read file
       //------------------------- socket intinalizing
   if(argc != 2)          //of user forget to insert the port number
     error("missing port number to complet establishment\n");
  
   portno=atoi(arg[1]);       //convert the port to int and check if it was within the rang
   if((portno&lt;=22000) || (portno&gt;=23000))
     error("your port number not valid .... pleas insert one in reng (22000,22999)\n");
  
   listenfd=socket(AF_INET,SOCK_STREAM,0);     //creat the listing socket
       bzero((char *)&amp;servaddr ,sizeof(servaddr));
       servaddr.sin_family=AF_INET;       //Ipv4
       servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
       servaddr.sin_port=htons(portno);
  
   bind(listenfd,(struct sockaddr *)&amp;servaddr,sizeof(servaddr));//bind the liten socket to specific port
   listen(listenfd,5);
       //-------------------------- server start to wait to handle requests
   for(;;)
   {
   printf("server wait for connections\n");
   bzero((char *)&amp;cliaddr ,sizeof(cliaddr));  //clear the previus client information
   clilen=sizeof(cliaddr);                //client informaton container
   connfd=accept(listenfd,(struct  sockaddr *)&amp;cliaddr,&amp;clilen);
   if(connfd&lt;0)
    error("error in accept this connection\n"); 
     //---------------------------------------        //start the secret hand chacking
   snprintf(buff,/*sizeof(buff)*/1,"%c",0x55);
   write(connfd,buff,sizeof(buff));
      //---------------------------------------       //read file name
  
    car=0xAA;
    read(connfd,buff,size(buff));
    printf("client reply is %c",buff[0]);
   if(car==buff[0])
       {
         printf("wait for file name \n");
        // bzero(buff,sizeof(buff));
     printf("1#%s\n",buff);
         read(connfd,buff,sizeof(buff));
     printf("2#%s\n",buff);
         strncpy(f_name,buff,sizeof(buff)-1);
         printf("file return name is %s\n",buff);
   }
   else
    error("this is not secure client\n");
  
   //--------------------------------------   if file found send 1 else 0
   fil_fd=open(f_name,O_RDONLY);      //file opent to be read only
   if(fil_fd &lt; 0)
   {
     snprintf(buff, sizeof(buff),"%d",0);
     write(connfd,buff,1);
     file("file is not found\n");     //retminate connection only
      break;
   }
   else
   {
    snprintf(buff, sizeof(buff),"%d",1);
        write(connfd,buff,1);
    printf("file exists.Send 1 to client\nreading and send the deil\n");
   //-----------------------------------reading and sending
   while(read(buff,1048,fil_fd)&gt;0)
            { 
               printf("%s \n\n",buff);
                write(connfd,buff,sizeof(buff)); //sending the file process
             }//end of uploading
  
    }//end of if_else
     //-------------------------------------------- close file resources " file"
    close(fil_fd);
    close(connfd);
     }//end of for()
       //--------------------------------------------prepair the server connection
    close(listenfd);
   exit(0);
  
      return 0;
      }//main()
  </code></pre>