绑定端口“地址已在使用中”时出错Unix中的TCP套接字编程

Question

I've gone through many posts and forums and I'm new to socket programming. Major parts of my code are similar to BIND ERROR : Address already in use

but then i changed my code so that i include "setsockopt" function like so:

const char* port="5555";
int opt=1;
portno=atoi(port);
//parameters for server address
serv_addr.sin_family=AF_INET;
serv_addr.sin_port=htons(portno);
serv_addr.sin_addr.s_addr=INADDR_ANY;
//bind the socket to the address
setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,(const char *)&opt,sizeof(int));


 if(bind(sockfd,(struct sockaddr*)&serv_addr,sizeof(serv_addr))<0)
{close(sockfd);
error("error in binding port!");
}

But still i get the error. I have to close the terminal and restart it in order to use the port again. I want to use a hardcoded port (like i mentioned in the code above)

                                                            Thanks a lot in advance

Answer 1

Check to see if the port is in use. Either telnet to that port or use netstat -a . It should be in use (as the error indicates) and kill the appropriate process. Perhaps using ps to find the process.

Answer 2

A port number can only be used by one application at a time. That means you can not start the same program twice expecting both to bind to the same port.

The SO_REUSEADDR is for when the socket bound to an address has already been closed, the same address (ip-address/port pair) can be used again directly.