title: C sockets raises error code 22, EINVAL - invalid argument
body: <p>The example code below works as as a server process. But when I add the line</p>
  
  <pre><code>pid_t childpid;
  </code></pre>
  
  <p>below</p>
  
  <pre><code>struct sockaddr_in servaddr, clientaddr;
  </code></pre>
  
  <p>it fails at line</p>
  
  <pre><code>connectfd = accept(listenfd, (struct sockaddr *) &amp;clientaddr, &amp;clientaddrlen);
  </code></pre>
  
  <p>with the error code 22, EINVAL - invalid argument. I'm new to sockets in C and I couldn't understand the problem, can you help me about this?</p>
  
  <p>Thanks.</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;sys/types.h&gt;
  #include &lt;sys/socket.h&gt; 
  #include &lt;linux/in.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;unistd.h&gt;
  #include &lt;errno.h&gt;
  
  extern int errno;
  
  int main()
  {
      int clientaddrlen, listenfd, connectfd, bytes_rcvd, listen_queue_size=1;
      short int port_no = 2000;
      char buffer[1000];
      struct sockaddr_in servaddr, clientaddr;
  
      printf("Server running at port #%d\n", port_no);
  
      // Create server socket.
      if ( (listenfd = socket(AF_INET, SOCK_STREAM, 0)) &lt; 0)
      {
          fprintf(stderr, "Cannot create server socket! errno=%d \n", errno);
          exit(-1);
      }
      printf("Server socket created\n");
  
      // Bind (attach) this process to the server socket.
      servaddr.sin_family = AF_INET;
      servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
      servaddr.sin_port = htons(port_no);
      bind(listenfd, (struct sockaddr *) &amp;servaddr, sizeof(servaddr));
      printf("Server socket is bound to port #%d\n", port_no);
  
      // Turn 'listenfd' to a listening socket. Listen queue size is 1.
      listen(listenfd,listen_queue_size);
      printf("Server listening with a queue of size %d. \n", listen_queue_size);
  
      // Wait for connection(s) from client(s).
      while (1)
      {
          connectfd = accept(listenfd, (struct sockaddr *) &amp;clientaddr, &amp;clientaddrlen);
          printf("A client has connected\n");
          if (recv(connectfd, buffer, sizeof(buffer), 0 ) &gt; 0)
              printf("Received message: %s\n", buffer);
          close(connectfd);
          printf("Server closed connection to client\n");
      }
  
      close(listenfd);
      return 0;
  }
  </code></pre>