[lwip-users] Checking whether the client is connected to the Server

[Teckinal Greek]

Hi, 
I am working on establishing Client-Server module over TCP.I have put a set up such that my PC acts as a normal server where I can connect it from some other PC's on my LAN using 'telnet ipaddress port' command and once I get connected with the server and can give some input from client computer so that it gets displayed on my server window(connection is established and data exchange takes place). 
Until here I can say that the server is working fine and what i wanted to implement is that now I wrote a code using lwIP API for the Altium Nanaboard so that my NB3000 acts like a client and i wanted it to get connected to my PC Server. 
Here goes my code for the client part which gets connected to the Server with given IPaddress. 

int tcp_client(void) 
{ 
char data[] = "Hello World"; 
struct netconn *conn; 
struct ip_addr ServAddr; 
err_t err; 
u16_t port; 

port = 7777; 

conn = netconn_new(NETCONN_TCP); 

IP4_ADDR(&ServAddr, 192,168,xx,xxx); 

err = netconn_connect(conn, &ServAddr, port); 

printf("err = %d", err); //err = -4 this is the value I am getting for err.

if(err == ERR_OK) 

netconn_write(conn, data, sizeof(data), NETCONN_NOCOPY); 

netconn_close(conn); 

netconn_delete(conn); 
} 
} 

here i open a new connection and connect it to Server using its IPaddress. 

Before that I wanted to check the connection whether it is connected or not, so what i did is i assigned a variable "err" and when I try to print it out on the terminal instrument and see the value it gives a value of "-4". 
Is this correct what I am doing here so that if i get a negative value that means the client is successfully connected to the server. 
If so how can i transfer the data "Hello World" on to my server and get it displayed there. 
Kind Regards,
Greek