Why address/port in use though socket was closed ??

2.7 Please explain the TIME_WAIT state.

Remember that TCP guarantees all data transmitted will be delivered, if at all possible. When you close a socket, the server goes into a TIME_WAIT state, just to be really really sure that all the data has gone through. When a socket is closed, both sides agree by sending messages to each other that they will send no more data. This, it seemed to me was good enough, and after the handshaking is done, the socket should be closed. The problem is two-fold. First, there is no way to be sure that the last ack was communicated successfully. Second, there may be “wandering duplicates” left on the net that must be dealt with if they are delivered.

Andrew Gierth ( andrewg@microlise.co.uk) helped to explain the closing sequence in the following usenet posting:

Assume that a connection is in ESTABLISHED state, and the client is about to do an orderly release. The client’s sequence no. is Sc, and the server’s is Ss. The pipe is empty in both directions.

   Client                                                   Server
   ======                                                   ======
   ESTABLISHED                                              ESTABLISHED
   (client closes)
   ESTABLISHED                                              ESTABLISHED
                <CTL=FIN+ACK><SEQ=Sc><ACK=Ss> ------->>
   FIN_WAIT_1
                <<-------- <CTL=ACK><SEQ=Ss><ACK=Sc+1>
   FIN_WAIT_2                                               CLOSE_WAIT
                <<-------- <CTL=FIN+ACK><SEQ=Ss><ACK=Sc+1>  (server closes)
                                                            LAST_ACK
                <CTL=ACK>,<SEQ=Sc+1><ACK=Ss+1> ------->>
   TIME_WAIT                                                CLOSED
   (2*msl elapses...)
   CLOSED

Global and Static Variables Intializations

Global and Static Variables should initialize with constant values.

All objects with static storage duration must be initialized (set to their initial values) before execution of main() starts. So a value which is not known at translation time cannot be used for initialization of static variables.

#include<stdio.h>

int initializer(void)

{

    return 50;

}

 

int main()

{

    static int i = initializer();

    printf(" value of i = %d", i);

    getchar();

    return 0;

}

O/P:

prog.c: In function 'main':
prog.c:9:17: error: initializer element is not constant
  static int i = initializer(); 
                 ^